Patent Publication Number: US-2023137812-A1

Title: Coalescing adjacent gather/scatter operations

Description:
RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 17/316,680, filed on May 10, 2021, entitled “COALESCING ADJACENT GATHER/SCATTER OPERATIONS”, which is a continuation of U.S. patent application Ser. No. 16/398,183, filed on Apr. 29, 2019, entitled “COALESCING ADJACENT GATHER/SCATTER OPERATIONS”, now U.S. Pat. No. 11,003,455, Issued on May 11, 2021, which is a continuation of U.S. patent application Ser. No. 15/601,003, filed on May 22, 2015, entitled “COALESCING ADJACENT GATHER/SCATTER OPERATIONS”, now U.S. Pat. No. 10,275,257, Issued on Apr. 30, 2019, which is a continuation of U.S. patent application Ser. No. 14/976,228, filed on Dec. 21, 2015, entitled “COALESCING ADJACENT GATHER/SCATTER OPERATIONS”, now U.S. Pat. No. 9,658,856, Issued on May 23, 2019, which is a continuation of U.S. patent application Ser. No. 13/997,784, filed on Jun. 25, 2013, entitled “COALESCING ADJACENT GATHER/SCATTER OPERATIONS”, now U.S. Pat. No. 9,348,601, Issued on May 24, 2016, which is hereby incorporated herein by this reference in its entirety and for all purposes. U.S. patent application Ser. No. 13/997,784 is itself a U.S. National Phase Application under 35 U.S.C. § 371 of International Application No. PCT/US2012/071688, filed Dec. 26, 2012, entitled “COALESCING ADJACENT GATHER/SCATTER OPERATIONS”. 
    
    
     TECHNICAL FIELD 
     The field of invention relates generally to processor architecture, and, more specifically, to techniques for coalescing gather scatter operations. 
     BACKGROUND ART 
     In order to fully utilize the single instruction, multiple data (SIMD) processor, gather instructions are used to read a set of (possibly) non-contiguous source data elements from memory and pack them together, typically into a single register. Scatter instructions do the reverse. In some instances, the data elements in memory are known to be contiguous to each other. Unfortunately, conventional gather and scatter instructions do not leverage off this known information, thus reducing the efficiency of the SIMD processor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention are illustrated by way of example and not limitation in the figures of the accompanying drawings in which like references indicate similar elements. 
         FIG.  1 A  illustrates a snippet of a source code. 
         FIG.  1 B  illustrates the resulting gather/scatter operations when the load/store instructions of the source code of  FIG.  1 A  are vectorized. 
         FIG.  2    is a block diagram of an execution pipeline of a processor or processor core according to one embodiment of the invention. 
         FIGS.  3 A through  3 E  are block diagrams illustrating the coalescing of three adjacent gather instructions. 
         FIG.  4    is a block diagram illustrating the coalescing of three adjacent gather instructions with a writemask. 
         FIG.  5    is a flow chart illustrating a method for processing a coalesced gather instruction. 
         FIG.  6    is a flow chart illustrating in further details the method of  FIG.  5   . 
         FIG.  7    is a block diagram illustrating the coalescing of three adjacent scatter instructions. 
         FIGS.  8 A through  8 H  are block diagrams illustrating an embodiment of coalescing adjacent gather instructions using current ISA. 
         FIG.  9 A  illustrates the pseudo-code for the operation of a new instruction vgatherp0123qpd. 
         FIG.  9 B  illustrates the pseudo-code for the operation of a new instruction vgatherp4567qpd. 
         FIG.  10 A  illustrates the pseudo-code for the operation of a new instruction vgatherp01qpd. 
         FIG.  10 B  illustrates the pseudo-code for the operation of a new instruction vgatherp23qpd. 
         FIG.  10 C  illustrates the pseudo-code for the operation of a new instruction vgatherp34qpd. 
         FIG.  10 D  illustrates the pseudo-code for the operation of a new instruction vgatherp67qpd. 
         FIG.  11 A  is a block diagram of the GENMUX unit for transposing the X components of the VPU banks. 
         FIG.  11 B  is a block diagram of the GENMUX unit for transposing the Y components of the VPU banks. 
         FIG.  12 A  illustrates an advanced vector extensions (AVX) instruction format according to one embodiment of the invention. 
         FIG.  12 B  illustrates an advanced vector extensions (AVX) instruction format according to another embodiment of the invention. 
         FIG.  12 C  illustrates an advanced vector extensions (AVX) instruction format according to another embodiment of the invention. 
         FIG.  13 A  is a block diagram illustrating a generic vector friendly instruction format and class A instruction templates thereof according to embodiments of the invention. 
         FIG.  13 B  is a block diagram illustrating the generic vector friendly instruction format and class B instruction templates thereof according to embodiments of the invention. 
         FIG.  14 A  is a block diagram illustrating a specific vector friendly instruction format according to one embodiment of the invention. 
         FIG.  14 B  is a block diagram illustrating a generic vector friendly instruction format according to another embodiment of the invention. 
         FIG.  14 C  is a block diagram illustrating a generic vector friendly instruction format according to another embodiment of the invention. 
         FIG.  14 D  is a block diagram illustrating a generic vector friendly instruction format according to another embodiment of the invention. 
         FIG.  15    is a block diagram of register architecture according to one embodiment of the invention. 
         FIG.  16 A  is a block diagram illustrating both an in-order pipeline and a register renaming, out-of-order issue/execution pipeline according to embodiments of the invention. 
         FIG.  16 B  is a block diagram illustrating both an embodiment of an in-order architecture core and a register renaming, out-of-order issue/execution architecture core to be included in a processor according to embodiments of the invention. 
         FIG.  17 A  is a block diagram of a processor core according to one embodiment of the invention. 
         FIG.  17 B  is a block diagram of a processor core according to another embodiment of the invention. 
         FIG.  18    is a block diagram of a processor according to embodiments of the invention. 
         FIG.  19    is a block diagram of a system in accordance with one embodiment of the invention. 
         FIG.  20    is a block diagram of a more specific system in accordance with an embodiment of the invention. 
         FIG.  21    is a block diagram of a more specific system in accordance with another embodiment of the invention. 
         FIG.  22    is a block diagram of a SoC in accordance with an embodiment of the invention. 
         FIG.  23    is a block diagram contrasting the use of a software instruction converter to convert binary instructions in a source instruction set to binary instructions in a target instruction set according to embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments and aspects of the inventions will be described with reference to details discussed below, and the accompanying drawings will illustrate the various embodiments. The following description and drawings are illustrative of the invention and are not to be construed as limiting the invention. Numerous specific details are described to provide a thorough understanding of various embodiments of the present invention. However, in certain instances, well-known or conventional details are not described in order to provide a concise discussion of embodiments of the present inventions. 
     Reference in the specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in conjunction with the embodiment can be included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification do not necessarily all refer to the same embodiment. 
       FIG.  1 A  illustrates a snippet of a source code. A very common pattern in source codes, as illustrated in  FIG.  1 A , is loading and storing contiguous elements of a structure into a sequence of registers. When the source code of  FIG.  1 A  is vectorized, each of the loads becomes a gather operation, and each of the stores becomes a scatter operation, as illustrated in  FIG.  1 B . 
     Referring now to  FIG.  1 B , gather operation 1 will perform eight memory reads, distributed through memory according to the eight indices in register zmm8 Gather operation 2 uses the same base (rax) and indices (zmm8), and performs almost exactly the same memory reads as gather operation 1, except it is offset by 8 bytes (because gather operation 2 has a displacement operand of 8). Gather operation 3 will perform the same memory reads as gather operation 1, except it is offset by 16 bytes (because gather operation 2 has a displacement operand of 16). Thus, the three gather operations produce a total of twenty four reads going through a memory execution cluster (MEC). The three gather operations also require the gather/scatter state machine (details to be provided below) to set up three times, which takes a significant number of cycles and transfers between a vector processing unit (VPU) and MEC. 
     Referring still to  FIG.  1 B , scatter operation 1 will perform eight memory writes, distributed through memory according to the eight indices in zmm8 Scatter operation 2 uses the same base (rax) and indices (zmm8), and performs almost exactly the same memory writes as scatter operation 1, except it is offset by 8 bytes (because scatter operation 2 has a displacement operand of 8). Scatter operation 3 will perform the same memory writes as scatter operation 1, except it is offset by 16 bytes (because scatter operation 2 has a displacement operand of 16). Thus, the three scatter operations produce a total of twenty four writes going through a memory execution cluster (MEC). The three scatter operations also require the gather/scatter state machine to set up three times, which takes a significant number of cycles and transfers between the VPU and MEC. 
     According to some embodiments, a new instruction set architecture (ISA) is utilized to perform coalesced gathering of contiguous data elements from memory and storing them into a set of multiple destination registers. The new ISA is also utilized to perform coalesced scattering of data elements from multiple source operands (e.g., registers, memory locations) by storing them in contiguous data elements in memory. A new set of processor instructions is used to implement the coalesced gathering/scattering with significant performance improvement with respect to existing processor instructions. The ISA is defined to operate on 128-bit SIMD registers (e.g., XMM registers), 256-bit SIMD registers (e.g., YMM registers), or 512-bit SIMD registers (e.g., ZMM registers). The SIMD register width discussed above are only for illustrative purposes. It will be appreciated that other the ISA may be defined to operate with other SIMD register widths. Embodiments of coalesced gathering techniques include reading from memory, using a single memory access, contiguous data elements and storing them in multiple destination storage locations. Embodiments of coalesced scattering techniques include reading data elements from multiple source registers, and storing them in memory contiguously in a single memory access. In the description provided herein, contiguous data elements shall mean that the data elements are located adjacent to each other in memory. Thus, the location in memory corresponding to the end of one data element is adjacent to the location in memory corresponding to the start of another data element. 
       FIG.  2    is a block diagram of a processor or processor core according to one embodiment of the invention. Referring to  FIG.  2   , processor  200  may represent any kind of instruction processing apparatuses or processing elements. A processing element refers to a thread, a process, a context, a logical processor, a hardware thread, a core, and/or any processing element, which shares access to other shared resources of the processor, such as reservation units, execution units, pipelines, and higher level caches/memory. A physical processor typically refers to an integrated circuit, which potentially includes any number of other processing elements, such as cores or hardware threads. A core often refers to logic located on an integrated circuit capable of maintaining an independent architectural state, where each independently maintained architectural state is associated with at least some dedicated execution resources. In one embodiment, processor  200  may be a general-purpose processor. Processor  200  may be any of various complex instruction set computing (CISC) processors, various reduced instruction set computing (RISC) processors, various very long instruction word (VLIW) processors, various hybrids thereof, or other types of processors entirely. Processor  200  may also represent one or more processor cores. 
     In one embodiment, processor  200  includes, but is not limited to, instruction decoder  202  to receive and decode instruction  210 . Instruction decoder  202  may generate and output one or more micro-operations, micro-code, entry points, microinstructions, other instructions, or other control signals, which reflect, or are derived from, instruction  210 . Instruction decoder  202  may be implemented using various different mechanisms. Examples of suitable mechanisms include, but are not limited to, microcode read only memories (ROMs), look-up tables, hardware implementations, programmable logic arrays (PLAs), and the like. 
     Execution units  204 , which may include an arithmetic logic unit (ALU), or another type of logic unit capable of performing operations based on instructions. As a result of instruction decoder  202  decoding the instruction  210 , execution unit  204  may receive one or more micro-operations, micro-code entry points, microinstructions, other instructions, or other control signals, which reflect, or are derived from, the instructions. Execution unit  204  may be operable as a result of instructions indicating one or more source operands (SRC) and to store a result in one or more destination operands (DEST) of a register set indicated by the instructions. Execution unit  204  may include circuitry or other execution logic (e.g., software combined with hardware and/or firmware) operable to execute instructions or other control signals derived from the instructions and perform an operation accordingly. 
     In one embodiment, instruction  210  may implicitly indicate and/or explicitly specify (e.g., through one or more dedicated fields or sets of bits) the source and destination operands. Examples of suitable sources and/or destination of the operands include registers, memory, immediate of the instruction, and combinations thereof. In various embodiments, the source and destination operands may be 8-bit, 16-bit, 32-bit, 64-bit, 128-bit, 256-bit, or 512-bit operands, although this is not required. 
     Some or all of the source and destination operands may be stored in storage resources  206  such as registers of a register set or memory. A register set may be part of a register file, along with potentially other registers, such as status registers, flag registers, etc. A register may be a storage location or device that may be used to store data. The register set may often be physically located on die with the execution unit(s). The registers may be visible from the outside of the processor or from a programmer&#39;s perspective. For example, instructions may specify operands stored in the registers. Various different types of registers are suitable, as long as they are capable of storing and providing data as described herein. The registers may or may not be renamed Examples of suitable registers include, but are not limited to, dedicated physical registers, dynamically allocated physical registers using register renaming, combinations of dedicated and dynamically allocated physical registers, etc. Alternatively, one or more of the source and destination operands may be stored in a storage location other than a register, such as, for example, a location in system memory. 
     According to one embodiment, execution unit  204  includes gather/scatter unit  208  that executes gather/scatter instructions that have been decoded by instruction decoder  202 . Below are embodiments of gathering and scattering instructions, which when executed by gather/scatter unit  208 , improve efficiency of a SIMD system by taking advantage of the fact that data elements are contiguously located in memory. 
     In one embodiment, the gather instruction is a coalesced gather instruction. The execution of this instruction by gather/scatter unit  208  stores contiguous data elements from memory into multiple destination operands. For example, in some embodiments, up to sixteen 32-bit or eight 64-bit floating-point data elements are conditionally packed into destination operands such as XMM, YMM, or ZMM registers. 
     The contiguous memory data elements to be loaded into destination operands are specified via a type of SIB (scale, index, and base) addressing. The coalesced gather instruction also includes a writemask. In some embodiments that use a dedicated mask register such as a “k” writemask (detailed later), the memory data elements will be loaded when their corresponding writemask bit indicates that they should be (for example, in some embodiments if the bit is a “1”). If a memory data element&#39;s corresponding writemask bit is not set, the corresponding data element of the destination operand (e.g., an XMM, YMM, or ZMM register) is left unchanged. 
     In one embodiment, the execution of a coalesced gather instruction will result in the entire writemask register being set to zero unless there is an exception. However, in some embodiments the instruction is suspended by an exception if at least one element has already been gathered (i.e., if the exception is triggered by an element other than the least significant one with its writemask bit set). When this happens the destination register and the writemask register are partially updated (those elements that have been gathered are placed into the destination register and have their mask bits set to zero). If any traps or interrupts are pending from already gathered elements, they may be delivered in lieu of the exception and the EFLAGS resume flag or equivalent is set to one so an instruction breakpoint is not re-triggered when the instruction is continued. 
     In some embodiments with 128-bit size destination registers, the instruction will gather up to four single-precision floating point values or two double-precision floating point values per destination register. In some embodiments with 256-bit size destination registers, the instruction will gather up to eight single-precision floating point values or four double-precision floating point values per destination register. In some embodiments with 512-bit size destination registers, the instruction will gather up to sixteen single-precision floating point values or eight double-precision floating point values per destination register. 
     In some embodiments, if the mask and destination registers are the same, this instruction delivers a general protection (GP) fault. Typically, the data element values may be read from memory in any order. However, faults are delivered in a right-to-left manner That is, if a fault is triggered by an element and delivered, all elements closer to the least significant bit (LSB) of the destination XMM, YMM, or ZMM will be completed (and non-faulting). Individual elements closer to the MSB may or may not be completed. If a given element triggers multiple faults, they are delivered in the conventional order. A given implementation of this instruction is repeatable—given the same input values and architectural state, the same set of elements to the left of the faulting one will be gathered. 
     The coalesced gather instruction may be implemented in several formats. In one embodiment, the coalesced gather instruction is defined as follows: 
     VGATHERQ4PD zmm3:zmm5:zmm6:zmm0{k1}, [rax+zmm9]//Format 0 
     where zmm3, zmm5, zmm6, and zmm0are destination vector register operands (such as a 128-, 256-, 512-bit register, etc.), k1 is a writemask operand (such as a 16-bit register examples of which are detailed later), rax is the base address, and zmm9 is a vector/array of indices. Note that the above format is described for illustration purposes only; other formats or orders of the operands may be implemented. In one embodiment, the base and a value stored in an index of the vector of indices are used to generate a memory address corresponding to the starting location of a block of contiguous data elements which are read and stored into the corresponding data elements (i.e., entries) of the destination operands. In some embodiments, the writemask is also of a different size (8 bits, 32 bits, etc.). Additionally, in some embodiments, not all bits of the writemask are utilized by the instruction. 
     In one embodiment, in the above format 0 of the instruction, the first destination operand is zmm3, the second destination operand is zmm5, the third destination operand is zmm6, and the fourth destination operand is zmm0 In another embodiment, the order of the operands is the reverse. In one embodiment, the order of these operands explicitly indicates the order in which contiguous data elements in memory will be loaded into the destination operands. Thus, in the above format 0 example, assuming the writemask indicates all data elements are to be updated (discussed in further details below), and assuming further that zmm3 is the first operand, data element at memory location “rax+zmm9[0]” is stored into zmm3[0]. The next three contiguous data elements, i.e., data elements at memory location “rax+zmm9[0]+size of(data element)”, at “rax+zmm9[0]+(2*size of(data element))”, and at “rax+zmm9[0]+(3*size of(data element))” are stored into the first data element of each of the subsequent destination operands, i.e., zmm5[0], zmm6[0], and zmm0[0], respectively. The second data element of each destination operand will be updated with contiguous data elements in memory using the same addressing scheme, e.g., zmm3[1] will be updated with the data element at memory location “rax+zmm9[1]”, and zmm5[1], zmm6[1], zmm0[1] will be loaded with the next three contiguous data elements in memory. 
     VGATHERQ4PD is the instruction&#39;s opcode. Typically, each operand is explicitly defined in the instruction. The size of the data elements may be defined in the “suffix” of the instruction. For instance, the suffix “PD” in the instruction VGATHERQ4PD may indicate that the data element is a double precision (i.e., 64 bits). In most embodiments, data elements are either 32 or 64 bits. If the data elements are 32 bits in size, and the operands are 512 bits in size, then there are sixteen (16) data elements per operand. In some embodiments, the number of data elements per operand implicitly indicates the number of indices that are present in the vector of indices (e.g., zmm9 in the above example.) In some embodiments, the number of operands is also explicitly defined in the instruction. For instance, in the above example, the “4” preceding the “PD” suffix may indicate that the instruction is coalescing four adjacent gather operations, i.e., the execution of the instruction results in writing four contiguous data elements from memory into corresponding data elements of four destination operands (e.g., zmm3, zmm5, zmm6, and zmm0 in the above example). In one embodiment, the block of contiguous data elements are read from memory in a single memory access. In one embodiment, the block of data elements are stored into all the destination operands in a single cycle. 
     In another embodiment, the coalesced gather instruction is defined as follows:
         VGATHERQ4PD zmm3-zmm0 {k1}, [rax+zmm9].//Format 1       

     The execution of the coalesced gather instruction having format 1 causes operations similar to those discussed above in the text relating to format 0 to be executed. The difference between format 0 and format 1 is that with format 1, the destination registers are specified as a range of registers. In the above example of format 1, the range of destination registers are bound by zmm3 and zmm0 Thus, implicitly, the destination registers are zmm3, zmm2, zmm1, and zmm0, where zmm2 and zmm1 are implied by the fact that the instruction explicitly indicates four destination registers are to be packed with data elements from memory. Note that in this embodiment, although the choice of the first destination register may be freely specified, it is a syntax error to specify a range of destination registers that is inconsistent with the number of destination registers explicitly indicated by the instruction. 
     In another embodiment, the coalesced gather instruction is defined as follows:
         VGATHERQ4PD zmm3-zmm0{k1}, [rax+zmm9].//Format 2       

     The execution of the coalesced gather instruction having format 2 causes operations similar to those discussed above in the text relating to format 0 to be executed. The difference between format 0 and format 2 is that with format 2, the destination registers are fixed. Thus, for instance, in the above example, the destination registers are fixed to zmm3, zmm2, zmm1, and zmm0 because the instruction explicitly indicates four destination registers are to be packed with data elements from memory. Note that in this embodiment, it is a syntax error to specify any destination registers other than “zmm3-zmm0” and this is specified only as an aid to readability. Although in the above example, the registers are fixed to “zmm3-zmm0”, it will be appreciated that the registers may be fixed to a range of other registers, e.g., “zmm4-zmm1”, or “zmm5-zmm2”, etc., or fixed to a set of non-contiguous registers. 
     In one embodiment, the data elements are fetched from memory and stored in temporary vector registers in a manner similar to that discussed above, prior to being stored in the destination registers. 
       FIGS.  3 A through  3 E  illustrate an example of an execution of a coalesced gather instruction, which coalesces three adjacent gather instructions according to certain embodiments. In this example, zmm8 holds the eight qword indices (i.e., each index is 64-bit wide) for three coalesced gather instructions. Since the destination registers (zmm0, zmm1, and zmm2) are each 512-bit wide, the size of each of the eight data element is 8-byte wide (i.e., double precision unit). Thus, each memory read fetches a 24-byte block of memory comprised of three double-precision values. In this illustration, the first, second and third destination operands are zmm0, zmm1, and zmm2, respectively. Thus, according to one embodiment, the first data element of each 24-byte block is stored into the corresponding data element of zmm0; the second data element of the block is stored into the corresponding data element of zmm1; and the third data element of the block is stored into the corresponding data element of zmm2 In these illustrations, the starting memory location of each block of data elements is the base address plus the value stored in the corresponding index of the array of indices, e.g., “rax+zmm8[0].” However, for readability purposes, the Figures shall denote “rax+zmm8[0]” simply as “zmm8[0]”. This notation applies to all subsequent Figures in the description. 
     Referring now to  FIG.  3 A , a 24-byte block of memory comprising of three double-precision data elements (i.e., each data element in the memory is 8-byte wide) is read from memory, where the first data element of the memory block starts at memory location “rax+zmm8[0]”, the second data element of the memory block is eight bytes away from the starting location of the block, and the third data element starts at sixteen bytes away from the starting memory location of the block. The first data element of the memory block is stored in the first data element of first destination register (i.e., zmm0[0]), the second data element of the memory block is stored in the first data element of the second destination register (i.e., zmm1[0]), and the third data element of the memory block is stored in the first data element of the third destination register (i.e., zmm2[0]). In one embodiment, the “first data element” of a destination register is the data element comprising of the least significant bits (LSB) of the destination register. In another embodiment, the “first data element” of a destination register comprises the most significant bits (MSB) of the destination register. 
       FIG.  3 B  illustrates the memory read of a second 24-byte block of memory. In this illustration, the memory block starts at “rax+zmm8[1]”. Since the second index of zmm8 (i.e., zmm8[1]) is used to generate the memory address, the contiguous data elements fetched are stored into the second data element of each destination register (i.e., zmm0[1], zmm1[1], and zmm2[1]). 
       FIG.  3 C  illustrates the memory read of a third 24-byte block of memory, starting at the memory location “rax+zmm8[2]”. Since the third index of zmm8 (i.e., zmm8[2]) is used to generate the memory address, the contiguous data elements fetched are stored into the third data element of each destination register (i.e., zmm0[2], zmm1[2], and zmm2[2]). 
       FIG.  3 D  illustrates the memory read of a fourth 24-byte block of memory, starting at the memory location “rax+zmm8[3]”. Since the fourth index of zmm8 (i.e., zmm8[3]) is used to generate the memory address, the contiguous data elements fetched are stored into the fourth data element of each destination register (i.e., zmm0[3], zmm1[3], and zmm2[3]). 
       FIG.  3 E  illustrates the destination registers zmm0, zmm1, and zmm2 completely packed with data elements from memory after four more 24-byte blocks of memory are read. 
       FIG.  4    illustrates another example of an execution of a coalesced gather instruction with the use of the writemask according to one embodiment. In this illustration, the base address is rax (not shown), and the vector/array of indices is zmm8 The illustration is an example of coalescing three adjacent gather operations, i.e., groups of three data elements contiguously located in memory are stored into data elements of three destination operands (zmm2, zmm1, and zmm0), according to the writemask k1. The writemask k1 has a hexadecimal value of 0xA3. In this illustration, the first, second and third destination operands are zmm2, zmm1, and zmm0, respectively. 
     The execution of the coalesced gather instruction causes gather/scatter unit  208  to generate a first memory address and determine if read 0 should be carried out. In one embodiment, the first address is the base address plus the value stored in the first index of the array of indices (i.e., “rax+zmm8[0]”), which points to a memory location of the first data element in memory to be stored in the first data element of the first destination operand (zmm2[0]). 
     In one embodiment, gather/scatter unit  208  determines if data elements should be read from memory and stored in the corresponding data elements of the destination operands according to the writemask bit values. In this illustration, the first (LSB) bit of the writemask, i.e., k1[0] is “1”, which in one embodiment, indicates that the first (LSB) data element of each destination operands should be updated. As a result, the data element at memory location “rax+zmm8[0]” having the value “2” and the next two contiguous data elements having the values “1” and “0”, are read from memory in a single memory access. In one embodiment, the data elements {2, 1, 0} are stored, in a single cycle, into the zmm2[0], zmm1[0], and zmm0[0], respectively. 
     Similarly, gather/scatter unit  208  generates a second address pointing to the memory location “rax+zmm8[1]” and determines if read 1 should be carried out. Like k1[0], the writemask bit k1[1] is also set to “1”, thus contiguous data elements {12, 11, 10} are fetched from memory starting at location “rax+zmm8[1]” and stored into zmm2[1], zmm1[1], and zmm0[1], respectively. 
     Gather/scatter unit  208  skips read 2 in this example because unlike k1[0] and k1[1], writemask bit k1[2] is set to “0”, which in one embodiment, indicates that the third data element of the destination operands should not be updated. As a result, zmm2[2], zmm1[2], and zmm0[2] remain unchanged, as indicated by the label “x” in  FIG.  4   . 
     Gather/scatter unit  208  performs the same logic as discussed above and determines that read 3, read 4, and read 6 should be skipped because k1[3], k1[4], and k1[6] are all set to “0”. Moreover, gather/scatter unit  208  determines that read 5 should be performed because k1[5] is set to “1”, and fetches the contiguous data elements {52, 51, 50} from memory starting at the address “rax+zmm8[5]” and stores them in zmm2[5], zmm1[5], and zmm0[5], respectively. Likewise, read 7 is performed because k1[7] is set to “1”, and contiguous data elements {72, 71, 70} are fetched from memory starting at location “rax+zmm8[7]” and stored into zmm2[7], zmm1[7], and zmm0[7], respectively. 
       FIG.  5    is a flow diagram illustrating a method  500  of processing a coalesced gather instruction according to one embodiment. Method  500  may be performed by processor  200  of  FIG.  2   . Referring to  FIG.  5   , at block  505 , a first instruction to gather contiguous data elements from memory is decoded. In one embodiment, the first instruction includes multiple operands, e.g., a first operand specifying a first storage location, a second operand specifying a second storage location, and a third operand specifying memory address. In one embodiment, the third operand includes a base address and an array of indices. The first instruction may also include a writemask. Exemplary sizes of operands have been previously detailed. 
     At block  510 , in response to the first instruction, contiguous first and second data elements are read from memory based on the memory address indicated by the third operand. In one embodiment, the contiguous data elements are read from memory using a single memory access. 
     At block  515 , the first instruction is executed to store contiguous first and second data elements from memory into a first entry of the first and second storage location, respectively. In one embodiment, the contiguous data elements are stored into the first and second storage locations in a single cycle. In one embodiment, the data elements are stored into temporary vector registers prior to being stored into destination operands. 
       FIG.  6    is a flow diagram illustrating a method  600  for processing a coalesced gather instruction. Method  600  may be performed by processor  200  of  FIG.  2   . In this illustration, it is assumed that some, if not all, of the operations  505 - 515  of  FIG.  5    have been performed previously. For example, at the least, a first instruction to gather data elements has been decoded. Referring to  FIG.  6   , at block  605 , a first address of a first data element in memory is generated according to a base address and a value stored in a first index of an array of indices. In one embodiment, the first address is the base address plus the value stored in the first index of the array of indices. 
     At block  610 , it is determined, according to a value of the first writemask bit, if the data elements are to be stored into the first entry of the first and second storage location. In one embodiment, the first writemask bit is the LSB bit of the writemask. When the writemask bit does not indicate that the data elements should be stored in the first and second storage location, then the first entry of the first and second storage location are left unchanged at block  630 , and the processing is completed. In one embodiment, a writemask bit having a value of “0” indicates that the data elements should not be stored in the first and second storage location. In another embodiment, the opposite convention is be used. 
     At block  615 , when the value stored in the first mask bit of the writemask indicates that the data elements should be stored in the first entry of the first and second storage location, then data elements are read from memory. In one embodiment, the first data element is located at the first address, and the second data element is contiguously located next to the first data element. In one embodiment, the data elements are read from memory in a single memory access. 
     At block  620 , the first and second data elements are stored into the first and second storage location. In one embodiment, the storage location is an array of entries (e.g., an array of data elements), and the first entry of the storage location is the LSB entry. In one embodiment, the data elements are stored into the first entry of the first and second storage location in a single cycle. In one embodiment, the first and second data elements are stored in vector registers prior to being stored into the first and second storage location. 
     At block  625 , the first writemask bit is cleared to indicate that the corresponding block of data elements have been fetched and stored in the first and second storage location, and the process is completed. 
     Referring back to  FIG.  1   , as discussed above, gather/scatter unit  208  executes gather and scatter instructions. In one embodiment, the scatter instruction is a coalesced scatter instruction. The execution of this instruction by gather/scatter unit  208  stores data elements from multiple source operands into contiguous memory locations such that the data elements are located adjacent to each other in memory. 
     The source operand data elements to be loaded into memory are specified via a type of SIB (scale, index, and base) addressing. The coalesced scatter instruction also includes a writemask. In some embodiments that use a dedicated mask register such as a “k” writemask, the source operand data elements will be loaded into memory when their corresponding writemask bit indicates that they should be (for example, in some embodiments if the bit is a “1”). If a data element&#39;s corresponding writemask bit is not set, the corresponding data element in memory is left unchanged. 
     In some embodiments with 128-bit size source registers, the instruction will scatter up to four single-precision floating point values or two double-precision floating point values per source register. In some embodiments with 256-bit size source registers, the instruction will scatter up to eight single-precision floating point values or four double-precision floating point values per source register. In some embodiments with 512-bit size source registers, the instruction will scatter up to sixteen single-precision floating point values or eight double-precision floating point values per source register. 
     The coalesced scatter instruction may be implemented in several formats. In one embodiment, the coalesced scatter instruction is defined as follows: 
     VSCATTERQ4PD[rax+zmm9] {k1}, zmm3:zmm5:zmm6zmm0//Format 3 
     where zmm3, zmm5, zmm6, and zmm0 are source vector register operands (such as a 128-, 256-, 512-bit register, etc.), k1 is a writemask operand (such as a 16-bit register examples of which are detailed later), rax is the base address, and zmm9 is a vector/array of indices. In one embodiment, the base and a value stored in an index of the vector of indices are used to generate a memory destination address where the first data element of the first source operand will be stored. In some embodiments, the writemask is also of a different size (8 bits, 32 bits, etc.). Additionally, in some embodiments, not all bits of the writemask are utilized by the instruction. 
     In one embodiment, in the above format 3 of the coalesced scatter instruction, the first source operand is zmm3, the second source operand is zmm5, the third source operand is zmm6, and the fourth source operand is zmm0 In another embodiment, the order of the source operands is the reverse, e.g., zmm3 is the fourth operand and zmm0 is the first operand. In one embodiment, the order of these operands explicitly indicates the order in which data elements from each source operand will be stored into contiguous memory. Thus, in the above format 3 example, assuming the writemask indicates all data elements are to be updated (discussed in further details below) and assuming further that the first source operand is zmm3, source operand data element zmm3101 is stored as the first data element in the contiguous block of memory starting at memory location “rax+zmm9[0]”. The data elements of the next three source operands, i.e., zmm5[0], zmm6[0], and zmm0[0] are stored in contiguous memory location, i.e., zmm5[0] is stored at “rax+zmm9[0]+size of(data element)”, zmm6[0] is stored at “rax+zmm9[0]+(2*size of(data element))”, and zmm0[0] is stored at “rax+zmm9[0]+(3*size of(data element))”. The second data element of each source operand will be stored in contiguous memory location starting at location “rax+zmm9[1]”, similar to how the first data elements of the source operands are stored. Thus, zmm3[1] is stored at “rax+zmm9[1]”; zmm5[1] is stored at “rax+zmm9[1]+size of(data element)”; zmm6[1] is stored at “rax+zmm9[1]+(2*size of(data element))”; and zmm0[1] is stored at “rax+zmm9[1]+(3*size of(data element))”. The remaining data elements of the source operands are stored into contiguous blocks of memory using the same logic. 
     VSCATTERQ4PD is the instruction&#39;s opcode. Typically, each operand is explicitly defined in the instruction. The size of the data elements may be defined in the “suffix” of the instruction. For instance, the suffix “PD” in the instruction VSCATTERQ4PD may indicate that the data element is a double precision (i.e., 64 bits). In most embodiments, data elements are either 32 or 64 bits. If the data elements are 32 bits in size, and the operands are 512 bits in size, then there are sixteen (16) data elements per operand. In some embodiments, the number of data elements per operand implicitly indicates the number of indices that are present in the vector of indices (e.g., zmm9 in the above example.) In one embodiment, the number of operands is also explicitly defined in the instruction. For instance, in the above example, the “4” preceding the “PD” suffix may indicate that the instruction is coalescing four adjacent scatter operations, i.e., the execution of the instruction results in writing data elements from four source operands into contiguous memory blocks of four data elements. In one embodiment, the source operand data elements are written to each contiguous memory block in a single memory access. 
     In another embodiment, the coalesced scatter instruction is defined as follows:
         VSCATTERQ4PD [rax+zmm9] {k1}, zmm3-zmm0.//Format 4       

     The execution of the coalesced scatter instruction having format 4 causes operations similar to those discussed above in the text relating to format 3 to be executed. The difference between format 3 and format 4 is that with format 4, the source operand registers are specified as a range of registers. In the above example of format 4, the range of source registers are bound by zmm3 and zmm0. Thus, implicitly, the source registers are zmm3, zmm2, zmm1, and zmm0, where zmm2 and zmm1 are implied by the fact that the instruction explicitly indicates data elements from four source registers are to be packed into memory. Note that in this embodiment, although the choice of the first source register may be freely specified, it is a syntax error to specify a range of source registers that is inconsistent with the number of source registers explicitly indicated by the instruction. 
     In another embodiment, the coalesced scatter instruction is defined as follows:
         VSCATTERQ4PD[rax+zmm9] {k1}, zmm3-zmm0.//Format 5       

     The execution of the coalesced scatter instruction having format 5 causes operations similar to those discussed above in the text relating to format 3 to be executed. The difference between format 3 and format 5 is that with format 5, the source registers are fixed. Thus, for instance, in the above example, the source registers are fixed to zmm3, zmm2, zmm1, and zmm0 because the instruction explicitly indicates data elements from four source registers are to be packed into memory. Note that in this embodiment, it is a syntax error to specify any source registers other than “zmm3-zmm0” and this is specified only as an aid to readability. Although in the above example, the registers are fixed to “zmm3-zmm0”, it will be appreciated that the registers may be fixed to a range of other registers, e.g., “zmm4-zmm1”, or “zmm5-zmm2”, etc. 
       FIG.  7    illustrates an example of an execution of a coalesced scatter instruction which includes the use of the writemask according to one embodiment. In this illustration, the base address is rax (not shown), and the vector/array of indices is zmm8. The illustration is an example of coalescing three adjacent scatter operations, i.e., data elements from a group of three source operands (zmm2, zmm1, and zmm0) are stored into contiguous memory, according to the writemask k1. The writemask k1 has a hexadecimal value of 0xA3. In this illustration, the first, second and third source operands are zmm2, zmm1, and zmm0, respectively. Again, this affects the ordering of the data elements stored into the memory block. 
     The execution of the coalesced scatter instruction causes gather/scatter unit  208  to generate a first address and determine if write 0 should be carried out. In one embodiment, the first address is the base address plus the value stored in the first index of the array of indices (i.e., “rax+zmm8[0]”), which points to a memory location of the start of the block of contiguous memory, where the first data element of the first source operand register (zmm2[0]) is to be stored. 
     In one embodiment, gather/scatter unit  208  determines if source operand data elements should be stored into memory according to the writemask bit values. In this illustration, the first (LSB) bit of the writemask, i.e., k1[0], is “1”, which in one embodiment, indicates that the first (LSB) data element of each source operands should be packed and stored into contiguous memory. As a result, source operand data elements {2, 1, 0} of zmm2[0], zmm1[0], and zmm0[0], respectively, are packed and stored as a block of contiguous memory, starting at the memory location “rax+zmm8[0]”. 
     Similarly, gather/scatter unit  208  generates a second address pointing to the memory location “rax+zmm8[1]” and determines if write 1 should be carried out. Like k1[0], the writemask bit k1[1] is also set to “1”, thus data elements {12, 11, 10} of zmm2[1], zmm1[1], and zmm0[0], respectively, are packed and stored into contiguous block of memory starting at the memory location “rax+zmm8[1]”. 
     Gather/scatter unit  208  skips write 2 in this example because unlike k1[0] and k1[1], writemask bit k1[2] is set to “0”, which in one embodiment, indicates that the third data element of the source operands should not be stored into memory. As result, zmm2[2], zmm1[2], and zmm0[2] are not written to memory. 
     Gather/scatter unit  208  performs the same logic as discussed above and determines that write 3, write 4, and write 6 should be skipped because k1[3], k1[4], and k1[6] are all set to “0”. Moreover, gather/scatter unit  208  determines that write 5 should be performed because k1[5] is set to “1”, and stores data elements {52, 51, 50} of source operands zmm2[5], zmm1[5], and zmm0[5] into contiguous memory starting at the address “rax+zmm8[5]”. Likewise, write 7 is performed because k1[7] is set to “1”, and data elements {72, 71, 70} of source operands zmm2[7], zmm1[7], and zmm0[7] are stored into contiguous memory starting at location “rax+zmm8[7]”. 
     In the above discussion, adjacent gather/scatter instructions are coalesced by a new ISA. It will be appreciated, however, that adjacent gather/scatter operations may also be coalesced using the current ISA by combining them “behind the scene”. For example, the three gather instructions: 
     vgatherqpd zmm0{k1}, [rax+zmm8+0] 
     vgatherqpd zmm1{k1}, [rax+zmm8+8] 
     vgatherqpd zmm2{k1}, [rax+zmm8+16] 
     may be performed by the current SIMD hardware as a single coalesced gather instruction. In one embodiment, in order to be combined as a coalesced gather instruction, the three gather instructions above must have the same operands, i.e., base, scale, index and writemask. Moreover, the instructions must have the right offsets/displacements. For example, the offset of each gather instruction must be a multiple of the size of the data element, so that each data element of an instruction is contiguously located in memory next to the data element of the preceding instruction. In one embodiment, when the above gather instructions are received, gather/scatter unit  208  assumes that they can be coalesced, and issues the combined reads, and then before retiring the instructions, checks that the instructions can be coalesced based on their operands. If not, the results are discarded and the instructions are re-executed as separate gathers. 
     In one embodiment, the following scatter operations may be similarly coalesced “behind the scene”: 
     vscatterqpd [rax+zmm8+0] {k1}, zmm0 
     vscatterqpd [rax+zmm8+8] {k1}, zmm1 
     vscatterqpd [rax+zmm8+16] {k1}, zmm2 
     In another embodiment, adjacent gather/scatter operations are coalesced using the current ISA by adding a prefix to the instructions to strongly hint that they will be fused/coalesced. For example, the gather instructions: 
     repvgatherqpd zmm0{k1}, [rax+zmm8+0] 
     repvgatherqpd zmm1{k1}, [rax+zmm8+8] 
     vgatherqpd zmm2{k1}, [rax+zmm8+16] 
     may be performed by the SIMD hardware as a single coalesced gather instruction. In this embodiment, the prefix “rep” assures the hardware that there are further gathers that can be coalesced coming along, and that it should buffer the first few until the last gather (which has no prefix) arrives. Similarly, the following strongly hinted scatter instructions may be coalesced: 
     repvscatterqpd [rax+zmm8+0] {k1}, zmm0 
     repvscatterqpd [rax+zmm8+8] {k1}, zmm1 
     vscatterqpd [rax+zmm8+16]{k1}, zmm2 
       FIGS.  8 A- 8 H  illustrate another embodiment of coalescing adjacent gather instructions using the current ISA. In this embodiment, the first gather instruction is sent to the gather/scatter unit  208 , which will assume that it is a first of three successive gather instructions. In this example, the data elements are each 8-byte wide (double precision unit), and since the destination operands zmm0, zmm1, and zmm2 are each 512-bit wide, there are eight data elements to be gathered from memory for each destination operand. For each data element to be gathered, gather/scatter unit  208  fetches at least eight bytes (the size of one data element) from memory, but it will attempt to fetch up to another sixteen bytes (two more double-precision values) without going over the end of the cache line. Gather/scatter unit  208  stores the first data element into the first destination operand and however many data elements it is able to read from memory into the corresponding data elements of the remaining destination operands. In other embodiments, gather/scatter unit  208  may store the data elements in a buffer, and copy the data from the buffer to the destination registers as the instructions retire. In this embodiment, gather/scatter unit  208  also keeps track of which data elements of the destination operands were not updated because the data elements were on a different cache line. In this embodiment, gather/scatter unit  208  may also maintain a signature cache that remembers what the current gather instruction looks like, e.g., how many data elements, their size, which base and index registers were used, and what immediate scale and offset to the base. 
     Referring now to  FIG.  8 A , the first memory read of the first gather instruction is performed. In this example, the first memory block of all three data elements can be read on the same cache line, and gather/scatter unit  208  is able to update the first data element of all three destination operands (zmm0[0], zmm1[0], and zmm2[0]). 
       FIG.  8 B  illustrates that the memory read by gather/scatter unit  208  for the second data element of the destination operands does not produce the entire 3-data element block. Specifically, the third data element of the block is on a different cache line. As a result, only the second data element of the first two destination operands (zmm0[1] and zmm1[1]) are updated with data elements from memory, and the second data element of the third destination operand (zmm2[1]) is not updated. 
       FIG.  8 C  illustrates that gather/scatter unit  208  is able to read the entire 3-data element block of memory during the third memory read. As a result, the third data element of each destination operand is updated. 
       FIG.  8 D  illustrates that the fourth memory read only returns a single double-precision value because the second and third data element is on a different cache line. Thus, only the fourth data element of the first destination operand (zmm0[3]) is updated. 
       FIG.  8 E  illustrates that after four more memory reads, all eight data elements of the first destination operand (zmm0) are updated. However, zmm1[3], zmm1[6], zmm2[1], zmm2[3], zmm2[5], and zmm2[6] have not been updated due to the fact that their respective data elements were on different cache lines. 
       FIG.  8 F  illustrates that once the first gather instruction is completed, i.e., all data elements of zmm0 have been updated, the instruction is retired, and the next gather instruction is processed. 
       FIG.  8 G  illustrates gather/scatter unit  208  processing the second gather instruction by performing a memory read for the fourth data element of the second destination operand (zmm1[3]). Gather/scatter unit  208  skipped the memory reads for first three data elements of zmm1 because they were updated during the updating of zmm0, as discussed above. Note also that in this illustration, the fourth data element of the third destination operand (zmm2[3]) is on the same cache line, and thus, zmm2[3] is also updated. 
       FIG.  8 H  illustrates gather/scatter unit  208  performing the last memory read to complete the updating of zmm1, and the second gather instruction is then retired. Although not shown, gather/scatter unit  208  will update the remaining data elements of zmm2 using similar procedures as discussed above, and retire the third gather instruction. 
     In another embodiment, adjacent gather and scatter operations are coalesced by transposing partial gather/scatter instructions. As discussed above, to gather a 2-element structure from eight indices currently requires two gather instructions: 
     vgatherqpd zmm0{k1}, [rax+zmm8+0] 
     vgatherqpd zmm1{k2}, [rax+zmm8+8]. 
     Assuming k1=k2=all “1s”, each of these instructions looks at all eight indices in zmm8 and performs a single 8-byte load. This results in sixteen cache line accesses, which is twice as many as required. In the following discussion, the x,y,z,w naming convention for data elements will be used, and the shorthand “x0” means “the double-precision value at address “rax+zmm8[0]+0”. Similarly, “y3” means “the double-precision value at address rax+zmm8[3]+8”. Given this naming convention, the execution of the above gather instructions produces the following results: 
     
       
         
           
               
               
               
               
               
               
               
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Zmm0 
                 x0 
                 x1 
                 x2 
                 x3 
                 x4 
                 x5 
                 x6 
                 x7 
               
               
                   
                 Zmm1 
                 y0 
                 y1 
                 y2 
                 y3 
                 y4 
                 y5 
                 y6 
                 y7 
               
               
                   
                   
               
            
           
         
       
     
     In one embodiment of the invention, a “partial” gather is performed that only uses some of the indices, but in return can load more data per index. This can be illustrated as a pair of partial gather instructions: 
     vgatherp0123qpd zmm0{k1}, [rax+zmm8+0] 
     vgatherp4567qpd zmm1{k2}, [rax+zmm8+0]. 
     The “0123” part of the first instruction indicates to gather/scatter unit  208  that the instruction only uses the first four indices of zmm8 and the first four bits of the writemask k1. Similarly, the “4567” of the second instruction indicates that it only uses the second four indices and writemask bits. Thus, the results are: 
     
       
         
           
               
               
               
               
               
               
               
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Zmm0 
                 x0 
                 x1 
                 x2 
                 x3 
                 y0 
                 y1 
                 y2 
                 y3 
               
               
                   
                 Zmm1 
                 y4 
                 y5 
                 y6 
                 y7 
                 x4 
                 x5 
                 x6 
                 x7 
               
               
                   
                   
               
            
           
         
       
     
     The reason for the odd ordering of the results will be explained in further details below. 
       FIG.  9 A  illustrates the pseudo-code for the operation of vgatherp0123qpd. If Load128 faults, it is handled by the same fault handling mechanisms as with the existing gather operations. Like the standard gather operations, it is important to clear the writemask bits as loads are performed so that the instruction can be restarted by the operating system (OS) after a fault. 
       FIG.  9 B  illustrates the pseudo-code for the operation of vgatherp4567qpd, which is similar to the pseudo-code for vgatherp0123qpd, with the differences highlighted. The benefit of using these two new instructions is that gather/scatter unit  208  is able to perform half the number of reads (eight rather than sixteen), even though each read is twice the size (128 bits rather than 64). Thus, this allows the sequence to run nearly twice as fast. 
     The above is a description of a 2-element structure. The equivalent for a 4-element structure is similar: 
     vgatherp01qpd zmm0{k1}, [rax+zmm8+0] 
     vgatherp23qpd zmm1{k2}, [rax+zmm8+0] 
     vgatherp34qpd zmm2{k1}, [rax+zmm8+0] 
     vgatherp67qpd zmm3{k2}, [rax+zmm8+0]. 
     Each of the above partial gather instructions performs only two reads, but each read is 256 bits in size. The results look like this: 
     
       
         
           
               
               
               
               
               
               
               
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Zmm0 
                 x0 
                 x1 
                 y0 
                 y1 
                 z0 
                 z1 
                 w0 
                 w1 
               
               
                   
                 Zmm1 
                 w2 
                 w3 
                 x2 
                 x3 
                 y2 
                 y3 
                 z2 
                 z3 
               
               
                   
                 Zmm2 
                 z4 
                 z5 
                 w4 
                 w5 
                 x4 
                 x5 
                 y4 
                 y5 
               
               
                   
                 Zmm3 
                 y6 
                 y7 
                 z6 
                 z7 
                 w6 
                 w7 
                 x6 
                 x7 
               
               
                   
                   
               
            
           
         
       
     
       FIGS.  10 A- 10 D  illustrate the pseudo-code for the partial gather instructions vgatherp01qpd, vgatherp23qpd, vgatherp34qpd, and vgatherp67qpd, respectively. 
     One of the advantages of the partial gather operations above is that they reduce the number of memory accesses. However, the disadvantage is that the data elements written to the vector registers are not in the format that is useful to standard vector arithmetic. In one embodiment, this formatting irregularity can be resolved by the existing shuffle/permute operations in the ISA. It is clearly possible to perform the 2-element transpose with 4 VPERMD instructions with the appropriate writemasks and the 4-element transpose in 16 VPERMD instructions with writemasks. Alternatively the newer VPERMI2 W instruction can permute data from two register sources, which can be used to halve the number of instructions required. 
     Even when using these existing permutation instructions, the new sequence of gathers can outperform the existing sequences because of the significant reduction in memory accesses. 
     In one embodiment, new special-purpose instructions are used to perform the transpose in only two or four instructions, by taking advantage of the fact that the VPUs are constructed as four “banks” of ALU and register file blocks, each bank handling 128 bits of the result. This means that each bank can read a different source register to the adjacent bank, allowing the gather/scatter unit  208  to read parts of up to four registers while only using a single read port per bank. This allows a single transpose instruction to read data from all four registers, and then send the combined 512-bit temporary result to the shuffle unit (called “GENMUX”) to reorder the data into the correct order. 
       FIGS.  11 A and  11 B  illustrate the construction of the zmm0 and zmm1 destination operands by transposing the results of the partial gathers. Referring to  FIG.  11 A , the GENMUX unit does not need to perform any permutation as the data is already in the correct ordering. However, as illustrated in  FIG.  11 B , the Y components need to be permutated to produce a correct ordering of data elements for zmm1 The Z and W components may be permutated in similar manner to produce zmm2 and zmm3. 
     In one embodiment, these operations are specified as multiple instructions with hardcoded selection and permutation controls. In another embodiment, they are specified more flexibly with the controls coming from either immediate values or from registers. Here, for simplicity we show them as hardcoded discrete instructions. 
     Using these transpose instructions allows the full gather+transpose operation to be performed very quickly. The 2-component version requires two gather and two transpose instructions: 
     vgatherp0123qpd zmm0{k1}, [rax+zmm8+0] 
     vgatherp4567qpd zmm1{k1}, [rax+zmm8+0] 
     vtranspose0123pd zmm10, zmm0, zmm1 
     vtranspose4567pd zmm11, zmm0, zmm1. 
     The 4-component version requires four gather and four transpose instructions: 
     vgatherp01qpd zmm0{k1}, [rax+zmm8+0] 
     vgatherp23qpd zmm1{k1}, [rax+zmm8+0] 
     vgatherp45qpd zmm2{k1}, [rax+zmm8+0] 
     vgatherp67qpd zmm3{k1}, [rax+zmm8+0] 
     vtranspose01pd zmm10, zmm0, zmm1, zmm2, zmm3 
     vtranspose23pd zmm11, zmm0, zmm1, zmm2, zmm3 
     vtranspose45pd zmm12, zmm0, zmm1, zmm2, zmm3 
     vtranspose67pd zmm13, zmm0, zmm1, zmm2, zmm3. 
     An instruction set, or instruction set architecture (ISA), is the part of the computer architecture related to programming, and may include the native data types, instructions, register architecture, addressing modes, memory architecture, interrupt and exception handling, and external input and output (I/O). The term instruction generally refers herein to macro-instructions—that is instructions that are provided to the processor (or instruction converter that translates (e.g., using static binary translation, dynamic binary translation including dynamic compilation), morphs, emulates, or otherwise converts an instruction to one or more other instructions to be processed by the processor) for execution—as opposed to micro-instructions or micro-operations (micro-ops)—that is the result of a processor&#39;s decoder decoding macro-instructions. 
     The ISA is distinguished from the microarchitecture, which is the internal design of the processor implementing the instruction set. Processors with different microarchitectures can share a common instruction set. For example, Intel® Pentium 4 processors, Intel® Core™ processors, and processors from Advanced Micro Devices, Inc. of Sunnyvale Calif. implement nearly identical versions of the x86 instruction set (with some extensions that have been added with newer versions), but have different internal designs. For example, the same register architecture of the ISA may be implemented in different ways in different microarchitectures using well-known techniques, including dedicated physical registers, one or more dynamically allocated physical registers using a register renaming mechanism (e.g., the use of a Register Alias Table (RAT), a Reorder Buffer (ROB), and a retirement register file; the use of multiple maps and a pool of registers), etc. Unless otherwise specified, the phrases register architecture, register file, and register are used herein to refer to that which is visible to the software/programmer and the manner in which instructions specify registers. Where a specificity is desired, the adjective logical, architectural, or software visible will be used to indicate registers/files in the register architecture, while different adjectives will be used to designation registers in a given microarchitecture (e.g., physical register, reorder buffer, retirement register, register pool). 
     An instruction set includes one or more instruction formats. A given instruction format defines various fields (number of bits, location of bits) to specify, among other things, the operation to be performed (opcode) and the operand(s) on which that operation is to be performed. Some instruction formats are further broken down though the definition of instruction templates (or subformats). For example, the instruction templates of a given instruction format may be defined to have different subsets of the instruction format&#39;s fields (the included fields are typically in the same order, but at least some have different bit positions because there are less fields included) and/or defined to have a given field interpreted differently. Thus, each instruction of an ISA is expressed using a given instruction format (and, if defined, in a given one of the instruction templates of that instruction format) and includes fields for specifying the operation and the operands. For example, an ADD instruction has a specific opcode and an instruction format that includes an opcode field to specify that opcode and operand fields to select operands (source1/destination and source2); and an occurrence of this ADD instruction in an instruction stream will have specific contents in the operand fields that select specific operands. 
     Scientific, financial, auto-vectorized general purpose, RMS (recognition, mining, and synthesis), and visual and multimedia applications (e.g., 2D/3D graphics, image processing, video compression/decompression, voice recognition algorithms and audio manipulation) often require the same operation to be performed on a large number of data items (referred to as “data parallelism”). Single Instruction Multiple Data (SIMD) refers to a type of instruction that causes a processor to perform an operation on multiple data items. SIMD technology is especially suited to processors that can logically divide the bits in a register into a number of fixed-sized data elements, each of which represents a separate value. For example, the bits in a 256-bit register may be specified as a source operand to be operated on as four separate 64-bit packed data elements (quad-word (Q) size data elements), eight separate 32-bit packed data elements (double word (D) size data elements), sixteen separate 16-bit packed data elements (word (W) size data elements), or thirty-two separate 8-bit data elements (byte (B) size data elements). This type of data is referred to as packed data type or vector data type, and operands of this data type are referred to as packed data operands or vector operands. In other words, a packed data item or vector refers to a sequence of packed data elements, and a packed data operand or a vector operand is a source or destination operand of a SIMD instruction (also known as a packed data instruction or a vector instruction). 
     By way of example, one type of SIMD instruction specifies a single vector operation to be performed on two source vector operands in a vertical fashion to generate a destination vector operand (also referred to as a result vector operand) of the same size, with the same number of data elements, and in the same data element order. The data elements in the source vector operands are referred to as source data elements, while the data elements in the destination vector operand are referred to a destination or result data elements. These source vector operands are of the same size and contain data elements of the same width, and thus they contain the same number of data elements. The source data elements in the same bit positions in the two source vector operands form pairs of data elements (also referred to as corresponding data elements; that is, the data element in data element position 0 of each source operand correspond, the data element in data element position 1 of each source operand correspond, and so on). The operation specified by that SIMD instruction is performed separately on each of these pairs of source data elements to generate a matching number of result data elements, and thus each pair of source data elements has a corresponding result data element. Since the operation is vertical and since the result vector operand is the same size, has the same number of data elements, and the result data elements are stored in the same data element order as the source vector operands, the result data elements are in the same bit positions of the result vector operand as their corresponding pair of source data elements in the source vector operands. In addition to this type of SIMD instruction, there are a variety of other types of SIMD instructions (e.g., that has only one or has more than two source vector operands, that operate in a horizontal fashion, that generates a result vector operand that is of a different size, that has a different size data elements, and/or that has a different data element order). It should be understood that the term destination vector operand (or destination operand) is defined as the direct result of performing the operation specified by an instruction, including the storage of that destination operand at a location (be it a register or at a memory address specified by that instruction) so that it may be accessed as a source operand by another instruction (by specification of that same location by the another instruction). 
     The SIMD technology, such as that employed by the Intel® Core™ processors having an instruction set including x86, MMX™, Streaming SIMD Extensions (SSE), SSE2, SSE3, SSE4.1, and SSE4.2 instructions, has enabled a significant improvement in application performance. An additional set of SIMD extensions, referred to the Advanced Vector Extensions (AVX) (AVX1 and AVX2) and using the Vector Extensions (VEX) coding scheme, has been, has been released and/or published (e.g., see Intel® 64 and IA-32 Architectures Software Developers Manual, October 2011; and see Intel® Advanced Vector Extensions Programming Reference, June 2011). 
     Embodiments of the instruction(s) described herein may be embodied in different formats. Additionally, exemplary systems, architectures, and pipelines are detailed below. Embodiments of the instruction(s) may be executed on such systems, architectures, and pipelines, but are not limited to those detailed. 
     VEX encoding allows instructions to have more than two operands, and allows SIMD vector registers to be longer than 128 bits. The use of a VEX prefix provides for three-operand (or more) syntax. For example, previous two-operand instructions performed operations such as A=A+B, which overwrites a source operand. The use of a VEX prefix enables operands to perform nondestructive operations such as A=B+C. 
       FIG.  12 A  illustrates an AVX instruction format including a VEX prefix  2102 , real opcode field  2130 , Mod R/M byte  2140 , SIB byte  2150 , displacement field  2162 , and IMM8  2172 .  FIG.  12 B  illustrates which fields from  FIG.  12 A  make up a full opcode field  2174  and a base operation field  2142 .  FIG.  12 C  illustrates which fields from  FIG.  12 A  make up a register index field  2144 . 
     VEX Prefix (Bytes  0 - 2 )  2102  is encoded in a three-byte form. The first byte is the Format Field  2140  (VEX Byte  0 , bits [ 7 : 0 ]), which contains an explicit C4 byte value (the unique value used for distinguishing the C4 instruction format). The second-third bytes (VEX Bytes  1 - 2 ) include a number of bit fields providing specific capability. Specifically, REX field  2105  (VEX Byte  1 , bits [ 7 - 5 ]) consists of a VEX.R bit field (VEX Byte  1 , bit [ 7 ]-R), VEX.X bit field (VEX byte  1 , bit [ 6 ]-X), and VEX.B bit field (VEX byte  1 , bit[ 5 ]-B). Other fields of the instructions encode the lower three bits of the register indexes as is known in the art (rrr, xxx, and bbb), so that Rrrr, Xxxx, and Bbbb may be formed by adding VEX.R, VEX.X, and VEX.B. Opcode map field  2115  (VEX byte  1 , bits [ 4 : 0 ]-mmmmm) includes content to encode an implied leading opcode byte. W Field  2164  (VEX byte  2 , bit [ 7 ]-W)—is represented by the notation VEX.W, and provides different functions depending on the instruction. The role of VEX.vvvv  2120  (VEX Byte  2 , bits [ 6 : 3 ]-vvvv) may include the following: 1) VEX.vvvv encodes the first source register operand, specified in inverted (1s complement) form and is valid for instructions with 2 or more source operands; 2) VEX.vvvv encodes the destination register operand, specified in is complement form for certain vector shifts; or 3) VEX.vvvv does not encode any operand, the field is reserved and should contain 1111b. If VEX.L  2168  Size field (VEX byte  2 , bit [ 2 ]-L)=0, it indicates 128 bit vector; if VEX.L=1, it indicates 256 bit vector. Prefix encoding field  2125  (VEX byte  2 , bits [ 1 : 0 ]-pp) provides additional bits for the base operation field. 
     Real Opcode Field  2130  (Byte  3 ) is also known as the opcode byte. Part of the opcode is specified in this field. MOD R/M Field  2140  (Byte  4 ) includes MOD field  2142  (bits [ 7 - 6 ]), Reg field  2144  (bits [ 5 - 3 ]), and R/M field  2146  (bits [ 2 - 0 ]). The role of Reg field  2144  may include the following: encoding either the destination register operand or a source register operand (the rrr of Rrrr), or be treated as an opcode extension and not used to encode any instruction operand. The role of R/M field  2146  may include the following: encoding the instruction operand that references a memory address, or encoding either the destination register operand or a source register operand. 
     Scale, Index, Base (SIB)—The content of Scale field  2150  (Byte  5 ) includes SS 2152  (bits [ 7 - 6 ]), which is used for memory address generation. The contents of SIB.xxx  2154  (bits [ 5 - 3 ]) and SIB.bbb  2156  (bits [ 2 - 0 ]) have been previously referred to with regard to the register indexes Xxxx and Bbbb. The Displacement Field  2162  and the immediate field (IMM8)  2172  contain address data. 
     A vector friendly instruction format is an instruction format that is suited for vector instructions (e.g., there are certain fields specific to vector operations). While embodiments are described in which both vector and scalar operations are supported through the vector friendly instruction format, alternative embodiments use only vector operations the vector friendly instruction format. 
       FIG.  13 A ,  FIG.  13 B , and  FIG.  13 C  are block diagrams illustrating a generic vector friendly instruction format and instruction templates thereof according to embodiments of the invention.  FIG.  13 A  is a block diagram illustrating a generic vector friendly instruction format and class A instruction templates thereof according to embodiments of the invention; while  FIG.  13 B  is a block diagram illustrating the generic vector friendly instruction format and class B instruction templates thereof according to embodiments of the invention. Specifically, a generic vector friendly instruction format  2200  for which are defined class A and class B instruction templates, both of which include no memory access  2205  instruction templates and memory access  2220  instruction templates. The term generic in the context of the vector friendly instruction format refers to the instruction format not being tied to any specific instruction set. 
     While embodiments of the invention will be described in which the vector friendly instruction format supports the following: a 64 byte vector operand length (or size) with 32 bit (4 byte) or 64 bit (8 byte) data element widths (or sizes) (and thus, a 64 byte vector consists of either 16 doubleword-size elements or alternatively, 8 quadword-size elements); a 64 byte vector operand length (or size) with 16 bit (2 byte) or 8 bit (1 byte) data element widths (or sizes); a 32 byte vector operand length (or size) with 32 bit (4 byte), 64 bit (8 byte), 16 bit (2 byte), or 8 bit (1 byte) data element widths (or sizes); and a 16 byte vector operand length (or size) with 32 bit (4 byte), 64 bit (8 byte), 16 bit (2 byte), or 8 bit (1 byte) data element widths (or sizes); alternative embodiments may support more, less and/or different vector operand sizes (e.g., 256 byte vector operands) with more, less, or different data element widths (e.g., 128 bit (16 byte) data element widths). 
     The class A instruction templates in  FIG.  13 A  include: 1) within the no memory access  2205  instruction templates there is shown a no memory access, full round control type operation  2210  instruction template and a no memory access, data transform type operation  2215  instruction template; and 2) within the memory access  2220  instruction templates there is shown a memory access, temporal  2225  instruction template and a memory access, non-temporal  2230  instruction template. The class B instruction templates in  FIG.  13 B  include: 1) within the no memory access  2205  instruction templates there is shown a no memory access, write mask control, partial round control type operation  2212  instruction template and a no memory access, write mask control, vsize type operation  2217  instruction template; and 2) within the memory access  2220  instruction templates there is shown a memory access, write mask control  2227  instruction template. 
     The generic vector friendly instruction format  2200  includes the following fields listed below in the order illustrated in  FIG.  13 A  and  FIG.  13 B . Format field  2240 —a specific value (an instruction format identifier value) in this field uniquely identifies the vector friendly instruction format, and thus occurrences of instructions in the vector friendly instruction format in instruction streams. As such, this field is optional in the sense that it is not needed for an instruction set that has only the generic vector friendly instruction format. Base operation field  2242 —its content distinguishes different base operations. 
     Register index field  2244 —its content, directly or through address generation, specifies the locations of the source and destination operands, be they in registers or in memory. These include a sufficient number of bits to select N registers from a P×Q (e.g. 32×512, 16×128, 32×1024, 64×1024) register file. While in one embodiment N may be up to three sources and one destination register, alternative embodiments may support more or less sources and destination registers (e.g., may support up to two sources where one of these sources also acts as the destination, may support up to three sources where one of these sources also acts as the destination, may support up to two sources and one destination). 
     Modifier field  2246 —its content distinguishes occurrences of instructions in the generic vector instruction format that specify memory access from those that do not; that is, between no memory access  2205  instruction templates and memory access  2220  instruction templates. Memory access operations read and/or write to the memory hierarchy (in some cases specifying the source and/or destination addresses using values in registers), while non-memory access operations do not (e.g., the source and destinations are registers). While in one embodiment this field also selects between three different ways to perform memory address calculations, alternative embodiments may support more, less, or different ways to perform memory address calculations. Augmentation operation field  2250 —its content distinguishes which one of a variety of different operations to be performed in addition to the base operation. This field is context specific. In one embodiment of the invention, this field is divided into a class field  2268 , an alpha field  2252 , and a beta field  2254 . The augmentation operation field  2250  allows common groups of operations to be performed in a single instruction rather than 2, 3, or 4 instructions. Scale field  2260 —its content allows for the scaling of the index field&#39;s content for memory address generation (e.g., for address generation that uses 2 scale *index+base). 
     Displacement Field  2262 A—its content is used as part of memory address generation (e.g., for address generation that uses 2 scale *index+base+displacement). Displacement Factor Field  2262 B (note that the juxtaposition of displacement field  2262 A directly over displacement factor field  2262 B indicates one or the other is used)—its content is used as part of address generation; it specifies a displacement factor that is to be scaled by the size of a memory access (N)—where N is the number of bytes in the memory access (e.g., for address generation that uses 2 scale *index+base+scaled displacement). Redundant low-order bits are ignored and hence, the displacement factor field&#39;s content is multiplied by the memory operands total size (N) in order to generate the final displacement to be used in calculating an effective address. The value of N is determined by the processor hardware at runtime based on the full opcode field  2274  (described later herein) and the data manipulation field  2254 C. The displacement field  2262 A and the displacement factor field  2262 B are optional in the sense that they are not used for the no memory access  2205  instruction templates and/or different embodiments may implement only one or none of the two. 
     Data element width field  2264 —its content distinguishes which one of a number of data element widths is to be used (in some embodiments for all instructions; in other embodiments for only some of the instructions). This field is optional in the sense that it is not needed if only one data element width is supported and/or data element widths are supported using some aspect of the opcodes. 
     Write mask field  2270 —its content controls, on a per data element position basis, whether that data element position in the destination vector operand reflects the result of the base operation and augmentation operation. Class A instruction templates support merging-writemasking, while class B instruction templates support both merging- and zeroing-writemasking. When merging, vector masks allow any set of elements in the destination to be protected from updates during the execution of any operation (specified by the base operation and the augmentation operation); in other one embodiment, preserving the old value of each element of the destination where the corresponding mask bit has a 0. In contrast, when zeroing vector masks allow any set of elements in the destination to be zeroed during the execution of any operation (specified by the base operation and the augmentation operation); in one embodiment, an element of the destination is set to 0 when the corresponding mask bit has a 0 value. A subset of this functionality is the ability to control the vector length of the operation being performed (that is, the span of elements being modified, from the first to the last one); however, it is not necessary that the elements that are modified be consecutive. Thus, the write mask field  2270  allows for partial vector operations, including loads, stores, arithmetic, logical, etc. While embodiments of the invention are described in which the write mask field&#39;s  2270  content selects one of a number of write mask registers that contains the write mask to be used (and thus the write mask field&#39;s  2270  content indirectly identifies that masking to be performed), alternative embodiments instead or additional allow the mask write field&#39;s  2270  content to directly specify the masking to be performed. 
     Immediate field  2272 —its content allows for the specification of an immediate. This field is optional in the sense that is it not present in an implementation of the generic vector friendly format that does not support immediate and it is not present in instructions that do not use an immediate. Class field  2268 —its content distinguishes between different classes of instructions. With reference to  FIG.  13 A  and  FIG.  13 B , the contents of this field select between class A and class B instructions. In  FIG.  13 A  and  FIG.  13 B , rounded corner squares are used to indicate a specific value is present in a field (e.g., class A  2268 A and class B  2268 B for the class field  2268  respectively in  FIG.  13 A  and  FIG.  13 B ). 
     In the case of the non-memory access  2205  instruction templates of class A, the alpha field  2252  is interpreted as an RS field  2252 A, whose content distinguishes which one of the different augmentation operation types are to be performed (e.g., round  2252 A. 1  and data transform  2252 A. 2  are respectively specified for the no memory access, round type operation  2210  and the no memory access, data transform type operation  2215  instruction templates), while the beta field  2254  distinguishes which of the operations of the specified type is to be performed. In the no memory access  2205  instruction templates, the scale field  2260 , the displacement field  2262 A, and the displacement scale filed  2262 B are not present. 
     In the no memory access full round control type operation  2210  instruction template, the beta field  2254  is interpreted as a round control field  2254 A, whose content(s) provide static rounding. While in the described embodiments of the invention the round control field  2254 A includes a suppress all floating point exceptions (SAE) field  2256  and a round operation control field  2258 , alternative embodiments may support may encode both these concepts into the same field or only have one or the other of these concepts/fields (e.g., may have only the round operation control field  2258 ). 
     SAE field  2256 —its content distinguishes whether or not to disable the exception event reporting; when the SAE field&#39;s  2256  content indicates suppression is enabled, a given instruction does not report any kind of floating-point exception flag and does not raise any floating point exception handler. 
     Round operation control field  2258 —its content distinguishes which one of a group of rounding operations to perform (e.g., Round-up, Round-down, Round-towards-zero and Round-to-nearest). Thus, the round operation control field  2258  allows for the changing of the rounding mode on a per instruction basis. In one embodiment of the invention where a processor includes a control register for specifying rounding modes, the round operation control field&#39;s  2250  content overrides that register value. 
     In the no memory access data transform type operation  2215  instruction template, the beta field  2254  is interpreted as a data transform field  2254 B, whose content distinguishes which one of a number of data transforms is to be performed (e.g., no data transform, swizzle, broadcast). 
     In the case of a memory access  2220  instruction template of class A, the alpha field  2252  is interpreted as an eviction hint field  2252 B, whose content distinguishes which one of the eviction hints is to be used (in  FIG.  13 A , temporal  2252 B. 1  and non-temporal  2252 B. 2  are respectively specified for the memory access, temporal  2225  instruction template and the memory access, non-temporal  2230  instruction template), while the beta field  2254  is interpreted as a data manipulation field  2254 C, whose content distinguishes which one of a number of data manipulation operations (also known as primitives) is to be performed (e.g., no manipulation; broadcast; up conversion of a source; and down conversion of a destination). The memory access  2220  instruction templates include the scale field  2260 , and optionally the displacement field  2262 A or the displacement scale field  2262 B. 
     Vector memory instructions perform vector loads from and vector stores to memory, with conversion support. As with regular vector instructions, vector memory instructions transfer data from/to memory in a data element-wise fashion, with the elements that are actually transferred is dictated by the contents of the vector mask that is selected as the write mask. 
     Temporal data is data likely to be reused soon enough to benefit from caching. This is, however, a hint, and different processors may implement it in different ways, including ignoring the hint entirely. Non-temporal data is data unlikely to be reused soon enough to benefit from caching in the 1st-level cache and should be given priority for eviction. This is, however, a hint, and different processors may implement it in different ways, including ignoring the hint entirely. 
     In the case of the instruction templates of class B, the alpha field  2252  is interpreted as a write mask control (Z) field  2252 C, whose content distinguishes whether the write masking controlled by the write mask field  2270  should be a merging or a zeroing. 
     In the case of the non-memory access  2205  instruction templates of class B, part of the beta field  2254  is interpreted as an RL field  2257 A, whose content distinguishes which one of the different augmentation operation types are to be performed (e.g., round  2257 A. 1  and vector length (VSIZE)  2257 A. 2  are respectively specified for the no memory access, write mask control, partial round control type operation  2212  instruction template and the no memory access, write mask control, VSIZE type operation  2217  instruction template), while the rest of the beta field  2254  distinguishes which of the operations of the specified type is to be performed. In the no memory access  2205  instruction templates, the scale field  2260 , the displacement field  2262 A, and the displacement scale filed  2262 B are not present. 
     In the no memory access, write mask control, partial round control type operation  2210  instruction template, the rest of the beta field  2254  is interpreted as a round operation field  2259 A and exception event reporting is disabled (a given instruction does not report any kind of floating-point exception flag and does not raise any floating point exception handler). 
     Round operation control field  2259 A—just as round operation control field  2258 , its content distinguishes which one of a group of rounding operations to perform (e.g., Round-up, Round-down, Round-towards-zero and Round-to-nearest). Thus, the round operation control field  2259 A allows for the changing of the rounding mode on a per instruction basis. In one embodiment of the invention where a processor includes a control register for specifying rounding modes, the round operation control field&#39;s  2250  content overrides that register value. 
     In the no memory access, write mask control, VSIZE type operation  2217  instruction template, the rest of the beta field  2254  is interpreted as a vector length field  2259 B, whose content distinguishes which one of a number of data vector lengths is to be performed on (e.g., 128, 256, or 512 byte). 
     In the case of a memory access  2220  instruction template of class B, part of the beta field  2254  is interpreted as a broadcast field  2257 B, whose content distinguishes whether or not the broadcast type data manipulation operation is to be performed, while the rest of the beta field  2254  is interpreted the vector length field  2259 B. The memory access  2220  instruction templates include the scale field  2260 , and optionally the displacement field  2262 A or the displacement scale field  2262 B. 
     With regard to the generic vector friendly instruction format  2200 , a full opcode field  2274  is shown including the format field  2240 , the base operation field  2242 , and the data element width field  2264 . While one embodiment is shown where the full opcode field  2274  includes all of these fields, the full opcode field  2274  includes less than all of these fields in embodiments that do not support all of them. The full opcode field  2274  provides the operation code (opcode). 
     The augmentation operation field  2250 , the data element width field  2264 , and the write mask field  2270  allow these features to be specified on a per instruction basis in the generic vector friendly instruction format. The combination of write mask field and data element width field create typed instructions in that they allow the mask to be applied based on different data element widths. 
     The various instruction templates found within class A and class B are beneficial in different situations. In some embodiments of the invention, different processors or different cores within a processor may support only class A, only class B, or both classes. For instance, a high performance general purpose out-of-order core intended for general-purpose computing may support only class B, a core intended primarily for graphics and/or scientific (throughput) computing may support only class A, and a core intended for both may support both (of course, a core that has some mix of templates and instructions from both classes but not all templates and instructions from both classes is within the purview of the invention). Also, a single processor may include multiple cores, all of which support the same class or in which different cores support different class. For instance, in a processor with separate graphics and general purpose cores, one of the graphics cores intended primarily for graphics and/or scientific computing may support only class A, while one or more of the general purpose cores may be high performance general purpose cores with out of order execution and register renaming intended for general-purpose computing that support only class B. Another processor that does not have a separate graphics core, may include one more general purpose in-order or out-of-order cores that support both class A and class B. Of course, features from one class may also be implemented in the other class in different embodiments of the invention. Programs written in a high level language would be put (e.g., just in time compiled or statically compiled) into an variety of different executable forms, including: 1) a form having only instructions of the class(es) supported by the target processor for execution; or 2) a form having alternative routines written using different combinations of the instructions of all classes and having control flow code that selects the routines to execute based on the instructions supported by the processor which is currently executing the code. 
       FIG.  14    is a block diagram illustrating a specific vector friendly instruction format according to embodiments of the invention.  FIG.  14    shows a specific vector friendly instruction format  2300  that is specific in the sense that it specifies the location, size, interpretation, and order of the fields, as well as values for some of those fields. The specific vector friendly instruction format  2300  may be used to extend the x86 instruction set, and thus some of the fields are similar or the same as those used in the existing x86 instruction set and extension thereof (e.g., AVX). This format remains consistent with the prefix encoding field, real opcode byte field, MOD R/M field, SIB field, displacement field, and immediate fields of the existing x86 instruction set with extensions. The fields from  FIG.  13    into which the fields from  FIG.  14    map are illustrated. 
     It should be understood that, although embodiments of the invention are described with reference to the specific vector friendly instruction format  2300  in the context of the generic vector friendly instruction format  2200  for illustrative purposes, the invention is not limited to the specific vector friendly instruction format  2300  except where claimed. For example, the generic vector friendly instruction format  2200  contemplates a variety of possible sizes for the various fields, while the specific vector friendly instruction format  2300  is shown as having fields of specific sizes. By way of specific example, while the data element width field  2264  is illustrated as a one bit field in the specific vector friendly instruction format  2300 , the invention is not so limited (that is, the generic vector friendly instruction format  2200  contemplates other sizes of the data element width field  2264 ). 
     The generic vector friendly instruction format  2200  includes the following fields listed below in the order illustrated in  FIG.  14 A . EVEX Prefix (Bytes  0 - 3 )  2302 —is encoded in a four-byte form. Format Field  2240  (EVEX Byte  0 , bits [ 7 : 0 ])—the first byte (EVEX Byte  0 ) is the format field  2240  and it contains 0x62 (the unique value used for distinguishing the vector friendly instruction format in one embodiment of the invention). The second-fourth bytes (EVEX Bytes  1 - 3 ) include a number of bit fields providing specific capability. 
     REX field  2305  (EVEX Byte  1 , bits [ 7 - 5 ])—consists of a EVEX.R bit field (EVEX Byte  1 , bit [ 7 ]-R), EVEX.X bit field (EVEX byte  1 , bit [ 6 ]-X), and  2257 BEX byte  1 , bit[ 5 ]-B). The EVEX.R, EVEX.X, and EVEX.B bit fields provide the same functionality as the corresponding VEX bit fields, and are encoded using is complement form, i.e. ZMM0 is encoded as 1111B, ZMM15 is encoded as 0000B. Other fields of the instructions encode the lower three bits of the register indexes as is known in the art (rrr, xxx, and bbb), so that Rrrr, Xxxx, and Bbbb may be formed by adding EVEX.R, EVEX.X, and EVEX.B. 
     REX′ field  2210 —this is the first part of the REX′ field  2210  and is the EVEX.R′ bit field (EVEX Byte  1 , bit [ 4 ]-R′) that is used to encode either the upper 16 or lower 16 of the extended 32 register set. In one embodiment of the invention, this bit, along with others as indicated below, is stored in bit inverted format to distinguish (in the well-known x86 32-bit mode) from the BOUND instruction, whose real opcode byte is 62, but does not accept in the MOD R/M field (described below) the value of 11 in the MOD field; alternative embodiments of the invention do not store this and the other indicated bits below in the inverted format. A value of 1 is used to encode the lower 16 registers. In other words, R′Rrrr is formed by combining EVEX.R′, EVEX.R, and the other RRR from other fields. 
     Opcode map field  2315  (EVEX byte  1 , bits [ 3 : 0 ]-mmmm)—its content encodes an implied leading opcode byte (0F, 0F 38, or 0F 3). Data element width field  2264  (EVEX byte  2 , bit [ 7 ]-W)—is represented by the notation EVEX.W. EVEX.W is used to define the granularity (size) of the datatype (either 32-bit data elements or 64-bit data elements). EVEX.vvvv  2320  (EVEX Byte  2 , bits [ 6 : 3 ]-vvvv)—the role of EVEX.vvvv may include the following: 1) EVEX.vvvv encodes the first source register operand, specified in inverted (1s complement) form and is valid for instructions with 2 or more source operands; 2) EVEX.vvvv encodes the destination register operand, specified in is complement form for certain vector shifts; or 3) EVEX.vvvv does not encode any operand, the field is reserved and should contain 1111b. Thus, EVEX.vvvv field  2320  encodes the 4 low-order bits of the first source register specifier stored in inverted (1s complement) form. Depending on the instruction, an extra different EVEX bit field is used to extend the specifier size to 32 registers. EVEX.U  2268  Class field (EVEX byte  2 , bit [ 2 ]-U)—If EVEX.U=0, it indicates class A or EVEX.U0; if EVEX.U=1, it indicates class B or EVEX.U1. 
     Prefix encoding field  2325  (EVEX byte  2 , bits [ 1 : 0 ]-pp)—provides additional bits for the base operation field. In addition to providing support for the legacy SSE instructions in the EVEX prefix format, this also has the benefit of compacting the SIMD prefix (rather than requiring a byte to express the SIMD prefix, the EVEX prefix requires only 2 bits). In one embodiment, to support legacy SSE instructions that use a SIMD prefix (66H, F2H, F3H) in both the legacy format and in the EVEX prefix format, these legacy SIMD prefixes are encoded into the SIMD prefix encoding field; and at runtime are expanded into the legacy SIMD prefix prior to being provided to the decoder&#39;s PLA (so the PLA can execute both the legacy and EVEX format of these legacy instructions without modification). Although newer instructions could use the EVEX prefix encoding field&#39;s content directly as an opcode extension, certain embodiments expand in a similar fashion for consistency but allow for different meanings to be specified by these legacy SIMD prefixes. An alternative embodiment may redesign the PLA to support the 2 bit SIMD prefix encodings, and thus not require the expansion. 
     Alpha field  2252  (EVEX byte  3 , bit [ 7 ]-EH; also known as EVEX.EH, EVEX.rs, EVEX.RL, EVEX.write mask control, and EVEX.N; also illustrated with α)—as previously described, this field is context specific. Beta field  2254  (EVEX byte  3 , bits [ 6 : 4 ]-SSS, also known as EVEX.s 2-0 , EVEX.r 2-0 , EVEX.rr1, EVEX.LL0, EVEX.LLB; also illustrated with βββ)—as previously described, this field is context specific. 
     REX′ field  2210 —this is the remainder of the REX′ field and is the EVEX.V′ bit field (EVEX Byte  3 , bit [ 3 ]-V′) that may be used to encode either the upper 16 or lower 16 of the extended 32 register set. This bit is stored in bit inverted format. A value of 1 is used to encode the lower 16 registers. In other words, V′ VVVV is formed by combining EVEX.V′, EVEX.vvvv. 
     Write mask field  2270  (EVEX byte  3 , bits [ 2 : 0 ]-kkk)—its content specifies the index of a register in the write mask registers as previously described. In one embodiment of the invention, the specific value EVEX.kkk=000 has a special behavior implying no write mask is used for the particular instruction (this may be implemented in a variety of ways including the use of a write mask hardwired to all ones or hardware that bypasses the masking hardware). 
     Real Opcode Field  2330  (Byte  4 ) is also known as the opcode byte. Part of the opcode is specified in this field. MOD R/M Field  2340  (Byte  5 ) includes MOD field  2342 , Reg field  2344 , and R/M field  2346 . As previously described, the MOD field&#39;s  2342  content distinguishes between memory access and non-memory access operations. The role of Reg field  2344  can be summarized to two situations: encoding either the destination register operand or a source register operand, or be treated as an opcode extension and not used to encode any instruction operand. The role of R/M field  2346  may include the following: encoding the instruction operand that references a memory address, or encoding either the destination register operand or a source register operand. 
     Scale, Index, Base (SIB) Byte (Byte  6 )—As previously described, the scale field&#39;s  2250  content is used for memory address generation. SIB.xxx  2354  and SIB.bbb  2356 —the contents of these fields have been previously referred to with regard to the register indexes Xxxx and Bbbb. Displacement field  2262 A (Bytes  7 - 10 )—when MOD field  2342  contains 10, bytes  7 - 10  are the displacement field  2262 A, and it works the same as the legacy 32-bit displacement (disp32) and works at byte granularity. 
     Displacement factor field  2262 B (Byte  7 )—when MOD field  2342  contains 01, byte  7  is the displacement factor field  2262 B. The location of this field is that same as that of the legacy x86 instruction set 8-bit displacement (disp8), which works at byte granularity. Since disp8 is sign extended, it can only address between −128 and 127 bytes offsets; in terms of 64 byte cache lines, disp8 uses 8 bits that can be set to only four really useful values −128, −64, 0, and 64; since a greater range is often needed, disp32 is used; however, disp32 requires 4 bytes. In contrast to disp8 and disp32, the displacement factor field  2262 B is a reinterpretation of disp8; when using displacement factor field  2262 B, the actual displacement is determined by the content of the displacement factor field multiplied by the size of the memory operand access (N). This type of displacement is referred to as disp8*N. This reduces the average instruction length (a single byte of used for the displacement but with a much greater range). Such compressed displacement is based on the assumption that the effective displacement is multiple of the granularity of the memory access, and hence, the redundant low-order bits of the address offset do not need to be encoded. In other words, the displacement factor field  2262 B substitutes the legacy x86 instruction set 8-bit displacement. Thus, the displacement factor field  2262 B is encoded the same way as an x86 instruction set 8-bit displacement (so no changes in the ModRM/SIB encoding rules) with the only exception that disp8 is overloaded to disp8*N. In other words, there are no changes in the encoding rules or encoding lengths but only in the interpretation of the displacement value by hardware (which needs to scale the displacement by the size of the memory operand to obtain a byte-wise address offset). Immediate field  2272  operates as previously described. 
       FIG.  14 B  is a block diagram illustrating the fields of the specific vector friendly instruction format  2300  that make up the full opcode field  2274  according to one embodiment of the invention. Specifically, the full opcode field  2274  includes the format field  2240 , the base operation field  2242 , and the data element width (W) field  2264 . The base operation field  2242  includes the prefix encoding field  2325 , the opcode map field  2315 , and the real opcode field  2330 . 
       FIG.  14 C  is a block diagram illustrating the fields of the specific vector friendly instruction format  2300  that make up the register index field  2244  according to one embodiment of the invention. Specifically, the register index field  2244  includes the REX field  2305 , the REX′ field  2310 , the MODR/M.reg field  2344 , the MODR/M.r/m field  2346 , the VVVV field  2320 , xxx field  2354 , and the bbb field  2356 . 
       FIG.  14 D  is a block diagram illustrating the fields of the specific vector friendly instruction format  2300  that make up the augmentation operation field  2250  according to one embodiment of the invention. When the class (U) field  2268  contains 0, it signifies EVEX.U0 (class A  2268 A); when it contains 1, it signifies EVEX.U1 (class B  2268 B). When U=0 and the MOD field  2342  contains 11 (signifying a no memory access operation), the alpha field  2252  (EVEX byte  3 , bit [ 7 ]-EH) is interpreted as the rs field  2252 A. When the rs field  2252 A contains a 1 (round  2252 A. 1 ), the beta field  2254  (EVEX byte  3 , bits [ 6 : 4 ]-SSS) is interpreted as the round control field  2254 A. The round control field  2254 A includes a one bit SAE field  2256  and a two bit round operation field  2258 . When the rs field  2252 A contains a 0 (data transform  2252 A. 2 ), the beta field  2254  (EVEX byte  3 , bits [ 6 : 4 ]-SSS) is interpreted as a three bit data transform field  2254 B. When U=0 and the MOD field  2342  contains 00, 01, or 10 (signifying a memory access operation), the alpha field  2252  (EVEX byte  3 , bit [ 7 ]-EH) is interpreted as the eviction hint (EH) field  2252 B and the beta field  2254  (EVEX byte  3 , bits [ 6 : 4 ]-SSS) is interpreted as a three bit data manipulation field  2254 C. 
     When U=1, the alpha field  2252  (EVEX byte  3 , bit [ 7 ]-EH) is interpreted as the write mask control (Z) field  2252 C. When U=1 and the MOD field  2342  contains 11 (signifying a no memory access operation), part of the beta field  2254  (EVEX byte  3 , bit [ 4 ]-S 0 ) is interpreted as the RL field  2257 A; when it contains a 1 (round  2257 A. 1 ) the rest of the beta field  2254  (EVEX byte  3 , bit [ 6 - 5 ]-S 2-1 ) is interpreted as the round operation field  2259 A, while when the RL field  2257 A contains a 0 (VSIZE  2257 .A 2 ) the rest of the beta field  2254  (EVEX byte  3 , bit [ 6 - 5 ]-S 2-1 ) is interpreted as the vector length field  2259 B (EVEX byte  3 , bit [ 6 - 5 ]-L 1-0 ). When U=1 and the MOD field  2342  contains 00, 01, or 10 (signifying a memory access operation), the beta field  2254  (EVEX byte  3 , bits [ 6 : 4 ]-SSS) is interpreted as the vector length field  2259 B (EVEX byte  3 , bit [ 6 - 5 ]-L 1-0 ) and the broadcast field  2257 B (EVEX byte  3 , bit [ 4 ]-B). 
       FIG.  15    is a block diagram of a register architecture  2400  according to one embodiment of the invention. In the embodiment illustrated, there are 32 vector registers  2410  that are 512 bits wide; these registers are referenced as zmm0 through zmm31. The lower order 256 bits of the lower 16 zmm registers are overlaid on registers ymm0-16. The lower order 128 bits of the lower 16 zmm registers (the lower order 128 bits of the ymm registers) are overlaid on registers xmm0-15. The specific vector friendly instruction format  2300  operates on these overlaid register file as illustrated in the below tables. 
     
       
         
           
               
               
               
               
             
               
                   
               
               
                 Adjustable 
                   
                   
                   
               
               
                 Vector  
                   
                   
                   
               
               
                 Length 
                 Class 
                 Operations 
                 Registers 
               
               
                   
               
             
            
               
                 Instruction 
                 A (FIG.  
                 2210,  
                 zmm registers 
               
               
                 Templates  
                 13A; 
                 2215, 
                 (the vector 
               
               
                 that do not  
                 U = 0) 
                 2225,  
                 length is  
               
               
                 include the  
                   
                 2230 
                 64 byte) 
               
               
                 vector length 
                 B (FIG.  
                 2212 
                 zmm registers 
               
               
                 field 2259B 
                 13B; 
                   
                 (the vector 
               
               
                   
                 U = 1) 
                   
                 length is  
               
               
                   
                   
                   
                 64 byte) 
               
               
                 Instruction 
                 B (FIG.  
                 2217,  
                 zmm, ymm, or 
               
               
                 Templates  
                 13B; 
                 2227 
                 xmm registers 
               
               
                 that do  
                 U = 1) 
                   
                 (the vector 
               
               
                 include the 
                   
                   
                 length is  
               
               
                 vector length 
                   
                   
                 64 byte, 
               
               
                 field 2259B 
                   
                   
                 32 byte, or 16 
               
               
                   
                   
                   
                 byte) depending 
               
               
                   
                   
                   
                 on the vector 
               
               
                   
                   
                   
                 length field 
               
               
                   
                   
                   
                 2259B 
               
               
                   
               
            
           
         
       
     
     In other words, the vector length field  2259 B selects between a maximum length and one or more other shorter lengths, where each such shorter length is half the length of the preceding length; and instructions templates without the vector length field  2259 B operate on the maximum vector length. Further, in one embodiment, the class B instruction templates of the specific vector friendly instruction format  2300  operate on packed or scalar single/double-precision floating point data and packed or scalar integer data. Scalar operations are operations performed on the lowest order data element position in an zmm/ymm/xmm register; the higher order data element positions are either left the same as they were prior to the instruction or zeroed depending on the embodiment. 
     Write mask registers  2415 —in the embodiment illustrated, there are 8 write mask registers (k0 through k7), each 64 bits in size. In an alternate embodiment, the write mask registers  2415  are 16 bits in size. As previously described, in one embodiment of the invention, the vector mask register k0 cannot be used as a write mask; when the encoding that would normally indicate k0 is used for a write mask, it selects a hardwired write mask of 0xFFFF, effectively disabling write masking for that instruction. 
     General-purpose registers  2425 —in the embodiment illustrated, there are sixteen 64-bit general-purpose registers that are used along with the existing x86 addressing modes to address memory operands. These registers are referenced by the names RAX, RBX, RCX, RDX, RBP, RSI, RDI, RSP, and R8 through R15. 
     Scalar floating point stack register file (x87 stack)  2445 , on which is aliased the MMX packed integer flat register file  2450 —in the embodiment illustrated, the x87 stack is an eight-element stack used to perform scalar floating-point operations on 32/64/80-bit floating point data using the x87 instruction set extension; while the MMX registers are used to perform operations on 64-bit packed integer data, as well as to hold operands for some operations performed between the MMX and XMM registers. 
     Alternative embodiments of the invention may use wider or narrower registers. Additionally, alternative embodiments of the invention may use more, less, or different register files and registers. 
     Processor cores may be implemented in different ways, for different purposes, and in different processors. For instance, implementations of such cores may include: 1) a general purpose in-order core intended for general-purpose computing; 2) a high performance general purpose out-of-order core intended for general-purpose computing; 3) a special purpose core intended primarily for graphics and/or scientific (throughput) computing. Implementations of different processors may include: 1) a CPU including one or more general purpose in-order cores intended for general-purpose computing and/or one or more general purpose out-of-order cores intended for general-purpose computing; and 2) a coprocessor including one or more special purpose cores intended primarily for graphics and/or scientific (throughput). Such different processors lead to different computer system architectures, which may include: 1) the coprocessor on a separate chip from the CPU; 2) the coprocessor on a separate die in the same package as a CPU; 3) the coprocessor on the same die as a CPU (in which case, such a coprocessor is sometimes referred to as special purpose logic, such as integrated graphics and/or scientific (throughput) logic, or as special purpose cores); and 4) a system on a chip that may include on the same die the described CPU (sometimes referred to as the application core(s) or application processor(s)), the above described coprocessor, and additional functionality. Exemplary core architectures are described next, followed by descriptions of processors and computer architectures. 
       FIG.  16 A  is a block diagram illustrating both anin-order pipeline and a register renaming, out-of-order issue/execution pipeline according to embodiments of the invention.  FIG.  16 B  is a block diagram illustrating both an embodiment of an in-order architecture core and an register renaming, out-of-order issue/execution architecture core to be included in a processor according to embodiments of the invention. The solid lined boxes illustrate the in-order pipeline and in-order core, while the optional addition of the dashed lined boxes illustrates the register renaming, out-of-order issue/execution pipeline and core. Given that the in-order aspect is a subset of the out-of-order aspect, the out-of-order aspect will be described. 
     In  FIG.  16 A , a processor pipeline  2500  includes a fetch stage  2502 , a length decode stage  2504 , a decode stage  2506 , an allocation stage  2508 , a renaming stage  2510 , a scheduling (also known as a dispatch or issue) stage  2512 , a register read/memory read stage  2514 , an execute stage  2516 , a write back/memory write stage  2518 , an exception handling stage  2522 , and a commit stage  2524 . 
       FIG.  16 B  shows processor core  2590  including a front end unit  2530  coupled to an execution engine unit  2550 , and both are coupled to a memory unit  2570 . The core  2590  may be a reduced instruction set computing (RISC) core, a complex instruction set computing (CISC) core, a very long instruction word (VLIW) core, or a hybrid or alternative core type. As yet another option, the core  2590  may be a special-purpose core, such as, for example, a network or communication core, compression engine, coprocessor core, general purpose computing graphics processing unit (GPGPU) core, graphics core, or the like. 
     The front end unit  2530  includes a branch prediction unit  2532  coupled to an instruction cache unit  2534 , which is coupled to an instruction translation lookaside buffer (TLB)  2536 , which is coupled to an instruction fetch unit  2538 , which is coupled to a decode unit  2540 . The decode unit  2540  (or decoder) may decode instructions, and generate as an output one or more micro-operations, micro-code entry points, microinstructions, other instructions, or other control signals, which are decoded from, or which otherwise reflect, or are derived from, the original instructions. The decode unit  2540  may be implemented using various different mechanisms. Examples of suitable mechanisms include, but are not limited to, look-up tables, hardware implementations, programmable logic arrays (PLAs), microcode read only memories (ROMs), etc. In one embodiment, the core  2590  includes a microcode ROM or other medium that stores microcode for certain macroinstructions (e.g., in decode unit  2540  or otherwise within the front end unit  2530 ). The decode unit  2540  is coupled to a rename/allocator unit  2552  in the execution engine unit  2550 . 
     The execution engine unit  2550  includes the rename/allocator unit  2552  coupled to a retirement unit  2554  and a set of one or more scheduler unit(s)  2556 . The scheduler unit(s)  2556  represents any number of different schedulers, including reservations stations, central instruction window, etc. The scheduler unit(s)  2556  is coupled to the physical register file(s) unit(s)  2558 . Each of the physical register file(s) units  2558  represents one or more physical register files, different ones of which store one or more different data types, such as scalar integer, scalar floating point, packed integer, packed floating point, vector integer, vector floating point, status (e.g., an instruction pointer that is the address of the next instruction to be executed), etc. 
     In one embodiment, the physical register file(s) unit  2558  comprises a vector registers unit, a write mask registers unit, and a scalar registers unit. These register units may provide architectural vector registers, vector mask registers, and general purpose registers. The physical register file(s) unit(s)  2558  is overlapped by the retirement unit  2554  to illustrate various ways in which register renaming and out-of-order execution may be implemented (e.g., using a reorder buffer(s) and a retirement register file(s); using a future file(s), a history buffer(s), and a retirement register file(s); using a register maps and a pool of registers; etc.). The retirement unit  2554  and the physical register file(s) unit(s)  2558  are coupled to the execution cluster(s)  2560 . 
     The execution cluster(s)  2560  includes a set of one or more execution units  2562  and a set of one or more memory access units  2564 . The execution units  2562  may perform various operations (e.g., shifts, addition, subtraction, multiplication) and on various types of data (e.g., scalar floating point, packed integer, packed floating point, vector integer, vector floating point). While some embodiments may include a number of execution units dedicated to specific functions or sets of functions, other embodiments may include only one execution unit or multiple execution units that all perform all functions. 
     The scheduler unit(s)  2556 , physical register file(s) unit(s)  2558 , and execution cluster(s)  2560  are shown as being possibly plural because certain embodiments create separate pipelines for certain types of data/operations (e.g., a scalar integer pipeline, a scalar floating point/packed integer/packed floating point/vector integer/vector floating point pipeline, and/or a memory access pipeline that each have their own scheduler unit, physical register file(s) unit, and/or execution cluster—and in the case of a separate memory access pipeline, certain embodiments are implemented in which only the execution cluster of this pipeline has the memory access unit(s)  2564 ). It should also be understood that where separate pipelines are used, one or more of these pipelines may be out-of-order issue/execution and the rest in-order. 
     The set of memory access units  2564  is coupled to the memory unit  2570 , which includes a data TLB unit  2572  coupled to a data cache unit  2574  coupled to a level 2 (L2) cache unit  2576 . In one embodiment, the memory access units  2564  may include a load unit, a store address unit, and a store data unit, each of which is coupled to the data TLB unit  2572  in the memory unit  2570 . The instruction cache unit  2534  is further coupled to a level 2 (L2) cache unit  2576  in the memory unit  2570 . The L2 cache unit  2576  is coupled to one or more other levels of cache and eventually to a main memory. 
     By way of example, the register renaming, out-of-order issue/execution core architecture may implement the pipeline  2500  as follows: 1) the instruction fetch  2538  performs the fetch and length decoding stages  2502  and  2504 ; 2) the decode unit  2540  performs the decode stage  2506 ; 3) the rename/allocator unit  2552  performs the allocation stage  2508  and renaming stage  2510 ; 4) the scheduler unit(s)  2556  performs the schedule stage  2512 ; 5) the physical register file(s) unit(s)  2558  and the memory unit  2570  perform the register read/memory read stage  2514 ; the execution cluster  2560  perform the execute stage  2516 ; 6) the memory unit  2570  and the physical register file(s) unit(s)  2558  perform the write back/memory write stage  2518 ; 7) various units may be involved in the exception handling stage  2522 ; and 8) the retirement unit  2554  and the physical register file(s) unit(s)  2558  perform the commit stage  2524 . 
     The core  2590  may support one or more instructions sets (e.g., the x86 instruction set (with some extensions that have been added with newer versions); the MIPS instruction set of MIPS Technologies of Sunnyvale, Calif.; the ARM instruction set (with optional additional extensions such as NEON) of ARM Holdings of Sunnyvale, Calif.), including the instruction(s) described herein. In one embodiment, the core  2590  includes logic to support a packed data instruction set extension (e.g., AVX1, AVX2, and/or some form of the generic vector friendly instruction format (U=0 and/or U=1) previously described), thereby allowing the operations used by many multimedia applications to be performed using packed data. 
     It should be understood that the core may support multithreading (executing two or more parallel sets of operations or threads), and may do so in a variety of ways including time sliced multithreading, simultaneous multithreading (where a single physical core provides a logical core for each of the threads that physical core is simultaneously multithreading), or a combination thereof (e.g., time sliced fetching and decoding and simultaneous multithreading thereafter such as in the Intel® Hyperthreading technology). 
     While register renaming is described in the context of out-of-order execution, it should be understood that register renaming may be used in an in-order architecture. While the illustrated embodiment of the processor also includes separate instruction and data cache units  2534 / 2574  and a shared L2 cache unit  2576 , alternative embodiments may have a single internal cache for both instructions and data, such as, for example, a Level 1 (L1) internal cache, or multiple levels of internal cache. In some embodiments, the system may include a combination of an internal cache and an external cache that is external to the core and/or the processor. Alternatively, all of the cache may be external to the core and/or the processor. 
       FIG.  17 A  and  FIG.  17 B  illustrate a block diagram of a more specific in-order core architecture, which core would be one of several logic blocks (including other cores of the same type and/or different types) in a chip. The logic blocks communicate through a high-bandwidth interconnect network (e.g., a ring network) with some fixed function logic, memory I/O interfaces, and other necessary I/O logic, depending on the application. 
       FIG.  17 A  is a block diagram of a single processor core, along with its connection to the on-die interconnect network  2602  and with its local subset of the Level 2 (L2) cache  2604 , according to embodiments of the invention. In one embodiment, an instruction decoder  2600  supports the x86 instruction set with a packed data instruction set extension. An L1 cache  2606  allows low-latency accesses to cache memory into the scalar and vector units. While in one embodiment (to simplify the design), a scalar unit  2608  and a vector unit  2610  use separate register sets (respectively, scalar registers  2612  and vector registers  2614 ) and data transferred between them is written to memory and then read back in from a level 1 (L1) cache  2606 , alternative embodiments of the invention may use a different approach (e.g., use a single register set or include a communication path that allow data to be transferred between the two register files without being written and read back). 
     The local subset of the L2 cache  2604  is part of a global L2 cache that is divided into separate local subsets, one per processor core. Each processor core has a direct access path to its own local subset of the L2 cache  2604 . Data read by a processor core is stored in its L2 cache subset  2604  and can be accessed quickly, in parallel with other processor cores accessing their own local L2 cache subsets. Data written by a processor core is stored in its own L2 cache subset  2604  and is flushed from other subsets, if necessary. The ring network ensures coherency for shared data. The ring network is bi-directional to allow agents such as processor cores, L2 caches and other logic blocks to communicate with each other within the chip. Each ring data-path is 1012-bits wide per direction. 
       FIG.  17 B  is an expanded view of part of the processor core in  FIG.  17 A  according to embodiments of the invention.  FIG.  17 B  includes an L1 data cache  2606 A part of the L1 cache  2604 , as well as more detail regarding the vector unit  2610  and the vector registers  2614 . Specifically, the vector unit  2610  is a 16-wide vector processing unit (VPU) (see the 16-wide ALU  2628 ), which executes one or more of integer, single-precision float, and double-precision float instructions. The VPU supports swizzling the register inputs with swizzle unit  2620 , numeric conversion with numeric convert units  2622 A-B, and replication with replication unit  2624  on the memory input. Write mask registers  2626  allow predicating resulting vector writes. 
       FIG.  18    is a block diagram of a processor  2700  that may have more than one core, may have an integrated memory controller, and may have integrated graphics according to embodiments of the invention. The solid lined boxes in  FIG.  18    illustrate a processor  2700  with a single core  2702 A, a system agent  2710 , a set of one or more bus controller units  2716 , while the optional addition of the dashed lined boxes illustrates an alternative processor  2700  with multiple cores  2702 A-N, a set of one or more integrated memory controller unit(s)  2714  in the system agent unit  2710 , and special purpose logic  2708 . 
     Thus, different implementations of the processor  2700  may include: 1) a CPU with the special purpose logic  2708  being integrated graphics and/or scientific (throughput) logic (which may include one or more cores), and the cores  2702 A-N being one or more general purpose cores (e.g., general purpose in-order cores, general purpose out-of-order cores, a combination of the two); 2) a coprocessor with the cores  2702 A-N being a large number of special purpose cores intended primarily for graphics and/or scientific (throughput); and 3) a coprocessor with the cores  2702 A-N being a large number of general purpose in-order cores. Thus, the processor  2700  may be a general-purpose processor, coprocessor or special-purpose processor, such as, for example, a network or communication processor, compression engine, graphics processor, GPGPU (general purpose graphics processing unit), a high-throughput many integrated core (MIC) coprocessor (including 30 or more cores), embedded processor, or the like. The processor may be implemented on one or more chips. The processor  2700  may be a part of and/or may be implemented on one or more substrates using any of a number of process technologies, such as, for example, BiCMOS, CMOS, or NMOS. 
     The memory hierarchy includes one or more levels of cache within the cores, a set or one or more shared cache units  2706 , and external memory (not shown) coupled to the set of integrated memory controller units  2714 . The set of shared cache units  2706  may include one or more mid-level caches, such as level 2 (L2), level 3 (L3), level 4 (L4), or other levels of cache, a last level cache (LLC), and/or combinations thereof. While in one embodiment a ring based interconnect unit  2712  interconnects the integrated graphics logic  2708 , the set of shared cache units  2706 , and the system agent unit  2710 /integrated memory controller unit(s)  2714 , alternative embodiments may use any number of well-known techniques for interconnecting such units. In one embodiment, coherency is maintained between one or more cache units  2706  and cores  2702 -A-N. 
     In some embodiments, one or more of the cores  2702 A-N are capable of multithreading. The system agent  2710  includes those components coordinating and operating cores  2702 A-N. The system agent unit  2710  may include for example a power control unit (PCU) and a display unit. The PCU may be or include logic and components needed for regulating the power state of the cores  2702 A-N and the integrated graphics logic  2708 . The display unit is for driving one or more externally connected displays. 
     The cores  2702 A-N may be homogenous or heterogeneous in terms of architecture instruction set; that is, two or more of the cores  2702 A-N may be capable of execution the same instruction set, while others may be capable of executing only a subset of that instruction set or a different instruction set. 
       FIG.  19    to  FIG.  23    are block diagrams of computer architectures. Other system designs and configurations known in the arts for laptops, desktops, handheld PCs, personal digital assistants, engineering workstations, servers, network devices, network hubs, switches, embedded processors, digital signal processors (DSPs), graphics devices, video game devices, set-top boxes, micro controllers, cell phones, portable media players, hand held devices, and various other electronic devices, are also suitable. In general, a huge variety of systems or electronic devices capable of incorporating a processor and/or other execution logic as disclosed herein are generally suitable. 
     Referring now to  FIG.  19   , shown is a block diagram of a system  2800  in accordance with one embodiment of the present invention. The system  2800  may include one or more processors  2810 ,  2815 , which are coupled to a controller hub  2820 . In one embodiment the controller hub  2820  includes a graphics memory controller hub (GMCH)  2890  and an Input/Output Hub (IOH)  2850  (which may be on separate chips); the GMCH  2890  includes memory and graphics controllers to which are coupled memory  2840  and a coprocessor  2845 ; the IOH  2850  is couples input/output (I/O) devices  2860  to the GMCH  2890 . Alternatively, one or both of the memory and graphics controllers are integrated within the processor (as described herein), the memory  2840  and the coprocessor  2845  are coupled directly to the processor  2810 , and the controller hub  2820  in a single chip with the IOH  2850 . 
     The optional nature of additional processors  2815  is denoted in  FIG.  19    with broken lines. Each processor  2810 ,  2815  may include one or more of the processing cores described herein and may be some version of the processor  2700 . 
     The memory  2840  may be, for example, dynamic random access memory (DRAM), phase change memory (PCM), or a combination of the two. For at least one embodiment, the controller hub  2820  communicates with the processor(s)  2810 ,  2815  via a multi-drop bus, such as a frontside bus (FSB), point-to-point interface such as QuickPath Interconnect (QPI), or similar connection  2895 . 
     In one embodiment, the coprocessor  2845  is a special-purpose processor, such as, for example, a high-throughput MIC processor, a network or communication processor, compression engine, graphics processor, GPGPU, embedded processor, or the like. In one embodiment, controller hub  2820  may include an integrated graphics accelerator. 
     There can be a variety of differences between the physical resources  2810 ,  2815  in terms of a spectrum of metrics of merit including architectural, microarchitectural, thermal, power consumption characteristics, and the like. 
     In one embodiment, the processor  2810  executes instructions that control data processing operations of a general type. Embedded within the instructions may be coprocessor instructions. The processor  2810  recognizes these coprocessor instructions as being of a type that should be executed by the attached coprocessor  2845 . Accordingly, the processor  2810  issues these coprocessor instructions (or control signals representing coprocessor instructions) on a coprocessor bus or other interconnect, to coprocessor  2845 . Coprocessor(s)  2845  accept and execute the received coprocessor instructions. 
     Referring now to  FIG.  20   , shown is a block diagram of a first more specific system  2900  in accordance with an embodiment of the present invention. As shown in  FIG.  20   , multiprocessor system  2900  is a point-to-point interconnect system, and includes a first processor  2970  and a second processor  2980  coupled via a point-to-point interconnect  2950 . Each of processors  2970  and  2980  may be some version of the processor  2700 . In one embodiment of the invention, processors  2970  and  2980  are respectively processors  2810  and  2815 , while coprocessor  2938  is coprocessor  2845 . In another embodiment, processors  2970  and  2980  are respectively processor  2810  coprocessor  2845 . 
     Processors  2970  and  2980  are shown including integrated memory controller (IMC) units  2972  and  2982 , respectively. Processor  2970  also includes as part of its bus controller units point-to-point (P-P) interfaces  2976  and  2978 ; similarly, second processor  2980  includes P-P interfaces  2986  and  2988 . Processors  2970 ,  2980  may exchange information via a point-to-point (P-P) interface  2950  using P-P interface circuits  2978 ,  2988 . As shown in  FIG.  20   , IMCs  2972  and  2982  couple the processors to respective memories, namely a memory  2932  and a memory  2934 , which may be portions of main memory locally attached to the respective processors. 
     Processors  2970 ,  2980  may each exchange information with a chipset  2990  via individual P-P interfaces  2952 ,  2954  using point to point interface circuits  2976 ,  2994 ,  2986 ,  2998 . Chipset  2990  may optionally exchange information with the coprocessor  2938  via a high-performance interface  2939 . In one embodiment, the coprocessor  2938  is a special-purpose processor, such as, for example, a high-throughput MIC processor, a network or communication processor, compression engine, graphics processor, GPGPU, embedded processor, or the like. 
     A shared cache (not shown) may be included in either processor or outside of both processors, yet connected with the processors via P-P interconnect, such that either or both processors&#39; local cache information may be stored in the shared cache if a processor is placed into a low power mode. Chipset  2990  may be coupled to a first bus  2916  via an interface  2996 . In one embodiment, first bus  2916  may be a Peripheral Component Interconnect (PCI) bus, or a bus such as a PCI Express bus or another third generation I/O interconnect bus, although the scope of the present invention is not so limited. 
     As shown in  FIG.  20   , various I/O devices  2914  may be coupled to first bus  2916 , along with a bus bridge  2918  which couples first bus  2916  to a second bus  2920 . In one embodiment, one or more additional processor(s)  2915 , such as coprocessors, high-throughput MIC processors, GPGPU&#39;s, accelerators (such as, e.g., graphics accelerators or digital signal processing (DSP) units), field programmable gate arrays, or any other processor, are coupled to first bus  2916 . In one embodiment, second bus  2920  may be a low pin count (LPC) bus. Various devices may be coupled to a second bus  2920  including, for example, a keyboard and/or mouse  2922 , communication devices  2927  and a storage unit  2928  such as a disk drive or other mass storage device which may include instructions/code and data  2930 , in one embodiment. Further, an audio I/O  2924  may be coupled to the second bus  2920 . Note that other architectures are possible. For example, instead of the point-to-point architecture of  FIG.  20   , a system may implement a multi-drop bus or other such architecture. 
     Referring now to  FIG.  21   , shown is a block diagram of a second more specific system  3000  in accordance with an embodiment of the present invention. Like elements in  FIG.  21    and  FIG.  22    bear like reference numerals, and certain aspects of  FIG.  20    have been omitted from  FIG.  21    in order to avoid obscuring other aspects of  FIG.  21   .  FIG.  21    illustrates that the processors  2970 ,  2980  may include integrated memory and I/O control logic (“CL”)  2972  and  2982 , respectively. Thus, the CL  2972 ,  2982  include integrated memory controller units and include I/O control logic.  FIG.  21    illustrates that not only are the memories  2932 ,  2934  coupled to the CL  2972 ,  2982 , but also that I/O devices  3014  are also coupled to the control logic  2972 ,  2982 . Legacy I/O devices  3015  are coupled to the chipset  2990 . 
     Referring now to  FIG.  22   , shown is a block diagram of a SoC  3100  in accordance with an embodiment of the present invention. Similar elements in  FIG.  18    bear like reference numerals. Also, dashed lined boxes are optional features on more advanced SoCs. In  FIG.  22   , an interconnect unit(s)  3102  is coupled to: an application processor  3110  which includes a set of one or more cores  202 A-N and shared cache unit(s)  2706 ; a system agent unit  2710 ; a bus controller unit(s)  2716 ; an integrated memory controller unit(s)  2714 ; a set or one or more coprocessors  3120  which may include integrated graphics logic, an image processor, an audio processor, and a video processor; an static random access memory (SRAM) unit  3130 ; a direct memory access (DMA) unit  3132 ; and a display unit  3140  for coupling to one or more external displays. In one embodiment, the coprocessor(s)  3120  include a special-purpose processor, such as, for example, a network or communication processor, compression engine, GPGPU, a high-throughput MIC processor, embedded processor, or the like. 
     Embodiments of the mechanisms disclosed herein may be implemented in hardware, software, firmware, or a combination of such implementation approaches. Embodiments of the invention may be implemented as computer programs or program code executing on programmable systems comprising at least one processor, a storage system (including volatile and non-volatile memory and/or storage elements), at least one input device, and at least one output device. 
     Program code, such as code  2930  illustrated in  FIG.  20   , may be applied to input instructions to perform the functions described herein and generate output information. The output information may be applied to one or more output devices, in known fashion. For purposes of this application, a processing system includes any system that has a processor, such as, for example; a digital signal processor (DSP), a microcontroller, an application specific integrated circuit (ASIC), or a microprocessor. 
     The program code may be implemented in a high level procedural or object oriented programming language to communicate with a processing system. The program code may also be implemented in assembly or machine language, if desired. In fact, the mechanisms described herein are not limited in scope to any particular programming language. In any case, the language may be a compiled or interpreted language. 
     One or more aspects of at least one embodiment may be implemented by representative instructions stored on a machine-readable medium which represents various logic within the processor, which when read by a machine causes the machine to fabricate logic to perform the techniques described herein. Such representations, known as “IP cores” may be stored on a tangible, machine readable medium and supplied to various customers or manufacturing facilities to load into the fabrication machines that actually make the logic or processor. 
     Such machine-readable storage media may include, without limitation, non-transitory, tangible arrangements of articles manufactured or formed by a machine or device, including storage media such as hard disks, any other type of disk including floppy disks, optical disks, compact disk read-only memories (CD-ROMs), compact disk rewritable&#39;s (CD-RWs), and magneto-optical disks, semiconductor devices such as read-only memories (ROMs), random access memories (RAMs) such as dynamic random access memories (DRAMs), static random access memories (SRAMs), erasable programmable read-only memories (EPROMs), flash memories, electrically erasable programmable read-only memories (EEPROMs), phase change memory (PCM), magnetic or optical cards, or any other type of media suitable for storing electronic instructions. 
     Accordingly, embodiments of the invention also include non-transitory, tangible machine-readable media containing instructions or containing design data, such as Hardware Description Language (HDL), which defines structures, circuits, apparatuses, processors and/or system features described herein. Such embodiments may also be referred to as program products. 
     In some cases, an instruction converter may be used to convert an instruction from a source instruction set to a target instruction set. For example, the instruction converter may translate (e.g., using static binary translation, dynamic binary translation including dynamic compilation), morph, emulate, or otherwise convert an instruction to one or more other instructions to be processed by the core. The instruction converter may be implemented in software, hardware, firmware, or a combination thereof. The instruction converter may be on processor, off processor, or part on and part off processor. 
       FIG.  23    is a block diagram contrasting the use of a software instruction converter to convert binary instructions in a source instruction set to binary instructions in a target instruction set according to embodiments of the invention. In the illustrated embodiment, the instruction converter is a software instruction converter, although alternatively the instruction converter may be implemented in software, firmware, hardware, or various combinations thereof.  FIG.  23    shows a program in a high level language  3202  may be compiled using an x86 compiler  3204  to generate x86 binary code  3206  that may be natively executed by a processor with at least one x86 instruction set core  3216 . The processor with at least one x86 instruction set core  3216  represents any processor that can perform substantially the same functions as an Intel processor with at least one x86 instruction set core by compatibly executing or otherwise processing (1) a substantial portion of the instruction set of the Intel x86 instruction set core or (2) object code versions of applications or other software targeted to run on an Intel processor with at least one x86 instruction set core, in order to achieve substantially the same result as an Intel processor with at least one x86 instruction set core. The x86 compiler  3204  represents a compiler that is operable to generate x86 binary code  3206  (e.g., object code) that can, with or without additional linkage processing, be executed on the processor with at least one x86 instruction set core  3216 . Similarly,  FIG.  23    shows the program in the high level language  3202  may be compiled using an alternative instruction set compiler  3208  to generate alternative instruction set binary code  3210  that may be natively executed by a processor without at least one x86 instruction set core  3214  (e.g., a processor with cores that execute the MIPS instruction set of MIPS Technologies of Sunnyvale, Calif. and/or that execute the ARM instruction set of ARM Holdings of Sunnyvale, Calif.). The instruction converter  3212  is used to convert the x86 binary code  3206  into code that may be natively executed by the processor without an x86 instruction set core  3214 . This converted code is not likely to be the same as the alternative instruction set binary code  3210  because an instruction converter capable of this is difficult to make; however, the converted code will accomplish the general operation and be made up of instructions from the alternative instruction set. Thus, the instruction converter  3212  represents software, firmware, hardware, or a combination thereof that, through emulation, simulation or any other process, allows a processor or other electronic device that does not have an x86 instruction set processor or core to execute the x86 binary code  3206 . 
     According to one embodiment, a processor includes an instruction decoder to decode a first instruction to gather data elements from memory, the first instruction having a first operand specifying a first storage location and a second operand specifying a first memory address storing a plurality of data elements. The processor further includes an execution unit coupled to the instruction decoder, in response to the first instruction, to read contiguous a first and a second of the data elements from a memory location based on the first memory address indicated by the second operand, and to store the first data element in a first entry of the first storage location and a second data element in a second entry of a second storage location corresponding to the first entry of the first storage location. In one embodiment, the first instruction further comprises a third operand specifying the second storage location. In one embodiment, the instruction decoder further decodes a second instruction having a third operand specifying the second storage location, and a fourth operand specifying a second memory address, the second memory address being offset from the first memory address by the size of a single data element. According to one aspect of the invention, the first instruction further comprises a prefix indicating to the instruction decoder and execution unit that the second instruction follows. In another embodiment, the execution unit predicts the existence of the second instruction. In one embodiment, the first entry of the first storage location is not contiguous to the second entry of the second storage location, and wherein the second storage location is specified by the first operand. According to one embodiment, the first data element is stored in a third entry of a third storage location prior to being stored in the first entry of the first storage location, and the second data element is stored in a fourth entry of a fourth storage location prior to being stored in the second entry of the second storage location. 
     Some portions of the preceding detailed descriptions have been presented in terms of algorithms and symbolic representations of operations on data bits within a computer memory. These algorithmic descriptions and representations are the ways used by those skilled in the data processing arts to most effectively convey the substance of their work to others skilled in the art. An algorithm is here, and generally, conceived to be a self-consistent sequence of operations leading to a desired result. The operations are those requiring physical manipulations of physical quantities. 
     It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the above discussion, it is appreciated that throughout the description, discussions utilizing terms such as those set forth in the claims below, refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system&#39;s registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices. 
     The techniques shown in the figures can be implemented using code and data stored and executed on one or more electronic devices. Such electronic devices store and communicate (internally and/or with other electronic devices over a network) code and data using computer-readable media, such as non-transitory computer-readable storage media (e.g., magnetic disks; optical disks; random access memory; read only memory; flash memory devices; phase-change memory) and transitory computer-readable transmission media (e.g., electrical, optical, acoustical or other form of propagated signals—such as carrier waves, infrared signals, digital signals). 
     The processes or methods depicted in the preceding figures may be performed by processing logic that comprises hardware (e.g. circuitry, dedicated logic, etc.), firmware, software (e.g., embodied on a non-transitory computer readable medium), or a combination of both. Although the processes or methods are described above in terms of some sequential operations, it should be appreciated that some of the operations described may be performed in a different order. Moreover, some operations may be performed in parallel rather than sequentially. 
     In the foregoing specification, embodiments of the invention have been described with reference to specific embodiments thereof. It will be evident that various modifications may be made thereto without departing from the broader spirit and scope of the invention as set forth in the following claims. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense.