Abstract:
Exemplary embodiments of the present invention disclose a method and system for replacing an unevaluated input that is constant at runtime to a group of instructions that calculates an output and can not modify the unevaluated input with invocation code that calls evaluation code. In a step, an exemplary embodiment identifies a group of instructions with an unevaluated input that is constant at runtime that calculates an output and can not modify the unevaluated input. In another step, an exemplary embodiment identifies an unevaluated input to the group of instructions that is constant at runtime. In another step, an exemplary embodiment generates an evaluation code that evaluates the unevaluated input. In another step, an exemplary embodiment replaces the unevaluated input with an invocation code that invokes the evaluation code.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to compiler optimizations and more specifically to enhancing program performance through the memoization of arguments of pure functions. 
     BACKGROUND 
     Many computer performance enhancement techniques are based on eliminating redundant computation. Memoization is a technique that may enhance computer program performance by decreasing computation by remembering the results of a previously executed function. A function is a group of program instructions that performs a specific task, by accepting input values, called arguments, and producing a result. A pure function is a function that always produces the same result given the same input arguments, regardless of program state, and produces no side effects, e.g., by changing the value of a variable that is visible outside the function, by altering one of its input arguments, or by performing input/output. A common memoization method records the arguments and results of an execution of a pure function and records the results. Pure functions are identified, and if a pure function is called, the arguments that are input and the results produced by the pure function are recorded if the results have not been recorded. On subsequent invocations of the same pure function, a lookup is performed, and if the arguments used in the current invocation have been used before, the recorded result associated with those arguments is used instead of executing the pure function. This approach has been found to be effective, especially in Java® programs. Java and all Java-based trademarks and logos are trademarks or registered trademarks of Oracle and/or its affiliates. 
     SUMMARY 
     Exemplary embodiments of the present invention disclose a method and system for replacing an unevaluated input that is constant at runtime to a group of instructions that calculates an output and cannot modify the unevaluated input with invocation code that calls evaluation code. In a step, an exemplary embodiment identifies a group of instructions with an unevaluated input that is constant at runtime that calculates an output and cannot modify the unevaluated input. In another step, an exemplary embodiment identifies an unevaluated input to the group of instructions that is constant at runtime. In another step, an exemplary embodiment generates an evaluation code that evaluates the unevaluated input. In another step, an exemplary embodiment replaces the unevaluated input with an invocation code that invokes the evaluation code. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a functional block diagram illustrating the operation of an analyzer program, in accordance with an embodiment of the present invention. 
         FIG. 2  depicts an example transformation of a pure function with an argument that is constant at runtime, in accordance with an embodiment of the present invention. 
         FIG. 3  depicts an example of code that implements an argument cache for a pure function depicted in  FIG. 2 , in accordance with an embodiment of the present invention. 
         FIG. 4  depicts a block diagram of components of a computing device, in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     As will be appreciated by one skilled in the art, aspects of the present invention may be embodied as a system, method or computer program product. Accordingly, aspects of the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “circuit,” “module” or “system.” Furthermore, aspects of the present invention may take the form of a computer program product embodied in one or more computer-readable medium(s) having computer readable program code/instructions embodied thereon. 
     Any combination of computer-readable media may be utilized. Computer-readable media may be a computer-readable signal medium or a computer-readable storage medium. A computer-readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of a computer-readable storage medium would include the following: a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory) a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In the context of this document, a computer-readable storage medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device. A computer-readable storage medium, as used herein, is not to be construed as being transitory signals per se, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through a waveguide or other transmission media (e.g., light pulses passing through a fiber-optic cable), or electrical signals transmitted through a wire. 
     A computer-readable signal medium may include a propagated data signal with computer-readable program code embodied therein, for example, in baseband or as part of a carrier wave. Such a propagated signal may take any of a variety of forms, including, but not limited to, electro-magnetic, optical, or any suitable combination thereof. A computer-readable signal medium may be any computer-readable medium that is not a computer-readable storage medium and that can communicate, propagate, or transport a program for use by or in connection with an instruction execution system, apparatus, or device. 
     Program code embodied on a computer-readable medium may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber cable, RF, etc., or any suitable combination of the foregoing. 
     Computer program code for carrying out operations for aspects of the present invention may be written in any combination of one or more programming languages, including an object oriented programming language such as Java®, Smalltalk, C++ or the like and conventional procedural programming languages, such as the “C” programming language or similar programming languages. The program code may execute entirely on a user&#39;s computer, partly on the user&#39;s computer, as a stand-alone software package, partly on the user&#39;s computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user&#39;s computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider). 
     Aspects of the present invention are described below with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. 
     These computer program instructions may also be stored in a computer-readable medium that can direct a computer, other programmable data processing apparatus, or other devices to function in a particular manner, such that the instructions stored in the computer-readable medium produce an article of manufacture including instructions which implement the function/act specified in the flowchart and/or block diagram block or blocks. 
     The computer program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other devices to cause a series of operational steps to be performed on the computer, other programmable apparatus or other devices to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus provide processes for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. 
     In an exemplary embodiment, a constant argument to a pure function in a Java program is calculated and cached so that the constant argument is not repeatedly calculated each time the pure function is executed. A pure function is a function that does not alter a one or more arguments to the function during an execution of the function, does not have side effects (e.g., modifying a global variable), and does not rely on external systems (e.g., I/O). If a pure function is found in a Java program, an argument to the pure function is analyzed to determine if the argument is constant at runtime, i.e., during the Java program&#39;s execution. An argument that is constant at runtime, a constant argument, may be complex and involve lengthy computations to evaluate, but the constant argument has a value that does not change between evaluations. 
     The present invention will now be described in detail with reference to the Figures.  FIG. 1  is a functional block diagram illustrating the operation of an analyzer program, in accordance with an embodiment of the present invention. 
     In various embodiments of the present invention, computer  101  is computing device that can be a standalone device, a server, a laptop computer, a tablet computer, a netbook computer, a personal computer (PC), or a desktop computer. In another embodiment, computer  101  represents a computing system utilizing clustered computers and components to act as a single pool of seamless resources. In general, computer  101  can be any computing device or a combination of devices with access to Java program  102  and Java program  113 , and is capable of running analyzer program  106 . Computer  101  may include internal and external hardware components, as depicted and described in further detail with respect to  FIG. 4 . 
     In an exemplary embodiment, a source code of Java program  102  is received by analyzer program  106  via input  107 . Java program  102  is analyzed by analyzer program  106  that is executing on computer  101  and analyzer program  106  identifies pure function  104  in Java program  102 . Analyzer program  106  identifies pure function  104  and determines that an argument to pure function  104 , constant argument  105  is constant at runtime. Analyzer program  106  alters Java program  102  and generates Java program  113  from Java program  102  as output  108 . When analyzer program  106  generates Java program  113 , analyzer program  106  alters pure function  104  and inserts an altered pure function  104 , transformed pure function  111 , in a place of pure function  104  into Java program  113 . Analyzer program  106  replaces constant argument  105  in pure function  104  with argument invocation code  112  in transformed pure function  111 . Argument invocation code  112  calls argument evaluation code  110  with call  114 . Argument evaluation code  110  invokes argument cache code  109 , which determines if constant argument  105  has previously been evaluated. If constant argument  105  has been previously evaluated, analyzer program  106  returns the value of constant argument  105  to argument evaluation code  110 , which in turn returns the value of constant argument  105 , via return  115 , to argument invocation code  112  in transformed pure function  111 . If the argument is found to be constant at run time, the argument is replaced in the Java program with code that executes an invocation code at runtime, which in turn executes an evaluation code at runtime that evaluates the argument if the argument has not been previously evaluated and remembers a value of the argument. If the pure function is executed again, the invocation code retrieves the value of the previously evaluated argument and the previously evaluated argument does not have to be evaluated again. 
       FIG. 2  and  FIG. 3  show a Java code that corresponds to Java program  102  and Java program  113 . Pure function  213 , transformed pure function  215 , argument evaluation code  214 , and argument cache code  303  correspond to pure function  104 , transformed pure function  111  argument evaluation code  110 , and argument cache code  109  respectively. 
       FIG. 2  shows a Java code of pure function  202  that is determined to be a pure function with two constant arguments, constant argument  206  and constant argument  207 , by analyzer program  106 . Constant argument  206  evaluates to a Date type variable with a value of 1020 milliseconds since midnight on Jan. 1, 1970 (known as “the epoc”) and constant argument  207  evaluates to a Date type variable with a value of 1000 milliseconds since the epoc. A word “new” in constant argument  206  causes a memory region to be allocated for a Date type variable which can involve an execution of many instructions. A creation of a Date type variable to be stored in an allocated memory can also involve an execution of many instructions. When argument  206  is evaluated, code  203  compares the value of argument  206  with Date type variable “var”, after which a Date type variable that argument  206  evaluates to and the memory region that holds the Date type variable is discarded. Constant argument  206  evaluates to a Date type variable with a value of 1020 milliseconds since the epoc every time that pure function  202  is called. 
     An evaluation of constant arguments  206  and  207  make a significant contribution to an execution time of a call to pure function  202  every time that pure function  202  is called. To reduce the execution time of pure function  202 , analyzer program  106  transforms pure function  202  into pure function  208  that evaluates an argument to pure function  208  only once, regardless of a number of times that pure function  208  is called. Constant argument  206  is replaced with call  209  to function “getPureFunction$0”, in code  210 . A code for a body of function $getPureFunction$0 is code  211 . When function $getPureFunction$0 in code  210  is called, code  211  is executed and returns a value of “TestPureFunctionPureFunctionHolder0.$pureFunction$0” on line  212 . A value of TestPureFunctionPureFunctionHolder0.$pureFunction$0 on line  212  is a value of constant variable $pureFunction$0  302  in class TestPureFunctionPureFunctionHolder0  301  in  FIG. 3 . $pureFunction$0 is a constant variable in class TestPureFunctionPureFunctionHolder0 that is evaluated only once, regardless of a number of times that pure function  208  is called. 
     A first time that that $getPureFunction$0 is called by pure function  208 , code  211  is executed and when “TestPureFunctionPureFunctionHolder0.$pureFunction$0” on line  212  is evaluated and returned, class TestPureFunctionPureFunctionHolder0 is referenced and initialized for a first time which causes constant variable $pureFunction$0  302  to be initialized to a Date type variable with a value of Date (1020L). Because $pureFunction$0  302  is a variable with a “static final Date” type, $pureFunction$0  302  is initialized once to a value of Date (1020L) and continues to have the value for a duration of an execution of Java program  113 . The value of $pureFunction$0  302  may be accessed again but $pureFunction$0  302  is never evaluated again during an execution of Java program  113  which reduces the execution time of Java program  113 . 
       FIG. 4  depicts a block diagram of components of computer system  101  in accordance with an illustrative embodiment of the present invention. It should be appreciated that  FIG. 4  provides only an illustration of one implementation and does not imply any limitations with regard to the environments in which different embodiments may be implemented. Many modifications to the depicted environment may be made, for example, an execution of a source code in a computer programming language other than Java can be enhanced with a technique described herein. 
     Computer system  101  includes communications fabric  402 , which provides communications between computer processor(s)  404 , memory  406 , persistent storage  408 , communications unit  410 , and input/output (I/O) interface(s)  412 . Communications fabric  402  can be implemented with any architecture designed for passing data and/or control information between processors (such as microprocessors, communications and network processors, etc.), system memory, peripheral devices, and any other hardware components within a system. For example, communications fabric  402  can be implemented with one or more buses. 
     Memory  406  and persistent storage  408  are computer-readable storage media. In this embodiment, memory  406  includes random access memory (RAM)  414  and cache memory  416 . In general, memory  406  can include any suitable volatile or non-volatile computer-readable storage media. 
     Hot spot monitor  105  and disk health monitor and scrub  106  are stored in persistent storage  408  for execution by one or more of the respective computer processors  404  via one or more memories of memory  406 . In this embodiment, persistent storage  408  includes a magnetic hard disk drive. Alternatively, or in addition to a magnetic hard disk drive, persistent storage  408  can include a solid state hard drive, a semiconductor storage device, read-only memory (ROM), erasable programmable read-only memory (EPROM), flash memory, or any other computer-readable storage media that is capable of storing program instructions or digital information. 
     The media used by persistent storage  408  may also be removable. For example, a removable hard drive may be used for persistent storage  408 . Other examples include optical and magnetic disks, thumb drives, and smart cards that are inserted into a drive for transfer onto another computer-readable storage medium that is also part of persistent storage  408 . 
     Communications unit  410 , in these examples, provides for communications with other data processing systems or devices, including resources of computer system  101 . In these examples, communications unit  410  includes one or more network interface cards. Communications unit  410  may provide communications through the use of either or both physical and wireless communications links. Java program  102 , analyzer program  106 , and Java program  113  may be downloaded to persistent storage  408  through communications unit  410 . 
     I/O interface(s)  412  allows for input and output of data with other devices that may be connected to computer system  101 . For example, I/O interface  412  may provide a connection to external devices  418  such as a keyboard, keypad, a touch screen, and/or some other suitable input device. External devices  418  can also include portable computer-readable storage media such as, for example, thumb drives, portable optical or magnetic disks, and memory cards. Software and data used to practice embodiments of the present invention, e.g., Java program  102 , analyzer program  106 , and Java program  113  can be stored on such portable computer-readable storage media and can be loaded onto persistent storage  408  via I/O interface(s)  412 . I/O interface(s)  412  also connect to a display  420 . 
     Display  420  provides a mechanism to display data to a user and may be, for example, a computer monitor. 
     The programs described herein are identified based upon the application for which they are implemented in a specific embodiment of the invention. However, it should be appreciated that any particular program nomenclature herein is used merely for convenience, and thus the invention should not be limited to use solely in any specific application identified and/or implied by such nomenclature. 
     The flowchart and block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.