i965/vs: split brw_vs_prog_data into generic and VS-specific parts.

This will allow the generic parts to be re-used for geometry shaders.

Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

v2: Put urb_read_length in the generic struct.
i965/vs: Make vec4_vs_visitor class derived from vec4_visitor.

This patch just creates the derived class; later patches will migrate
VS-specific functions and data structures from the base class into the
derived class.

Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
i965/vs: Make some vec4_visitor functions virtual.

This patch makes the following vec4_visitor functions virtual, since
they will need to be implemented differently for vertex and geometry
shaders.  Some of the functions are renamed to reflect their generic
purpose, rather than their VS-specific behaviour:

- setup_attributes
- emit_attribute_fixups (renamed to emit_prolog)
- emit_vertex_program_code (renamed to emit_program_code)
- emit_urb_writes (renamed to emit_thread_end)

Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
i965/vs: Add virtual function make_reg_for_system_value().

The system values handled by vec4_visitor::visit(ir_variable *) are
VS-specific (vertex ID and instance ID).  This patch moves the
handling of those values into a new virtual function,
make_reg_for_system_value(), so that this VS-specific code won't be
inherited by geomtry shaders.

Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
i965/vs: move ARB_vertex_program functions to vec4_vs_visitor.

This patch moves functions from vec4_visitor to vec4_vs_visitor that
deal with ARB (assembly) vertex programs.  There's no point in having
these functions in the base class since we don't intend to support
assembly programs for the GS stage.  The following functions are
moved:

- setup_vp_regs
- get_vp_dst_reg
- get_vp_src_reg

Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
i965/vs: move VS-specific data members to vs_vec4_visitor.

This patch moves the following data structures from vec4_visitor to
vec4_vs_visitor, since they contain VS-specific data:

- struct brw_vs_compile *c
- struct brw_vs_prog_data *prog_data
- src_reg *vp_temp_regs
- src_reg vp_addr_reg

Since brw_vs_compile and brw_vs_prog_data also contain vec4-generic
data, the following pointers are added to the base class, to allow it
to access the vec4-generic portions of these data structures:

- struct brw_vec4_compile *vec4_compile
- struct brw_vec4_prog_key *vec4_key
- struct brw_vec4_prog_data *vec4_prog_data

Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
i965/vs: Generalize data structures pointed to by vec4_generator.

This patch removes the following field from vec4_generator, since it
is not used:

- struct brw_vs_compile *c

And changes the following field:

- struct gl_vertex_program *vp => struct gl_program *glprog

With these changes, vec4_generator no longer refers to any VS-specific
data structures.  This will pave the way for re-using it for geometry
shaders.

Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
i965/vs: rename vec4_generator::generate_vs_instruction.

Since this function is going to get used for geometry shaders too, it
deserves a more generic name: generate_vec4_instruction.

Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
i965/vs: Generalize vertex emission code in preparation for GS.

This patch introduces a new function, vec4_visitor::emit_vertex(),
which contains the code for emitting vertices that will need to be
common between the vertex and geometry shaders.

Geometry shaders will need to use a different message header, and a
different opcode, for their URB writes, so we introduce virtual
functions emit_urb_write_header() and emit_urb_write_opcode() to take
care of the GS-specific behaviours.

Also, since vertex emission happens at the end of the VS, but in the
middle of the GS, we need to be sure to only call
emit_shader_time_end() during VS vertex emission.  We accomplish this
by moving the call to emit_shader_time_end() into the VS
implementation of emit_urb_write_opcode().

Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
i965/vs: Generalize attribute setup code in preparation for GS.

This patch introduces a new function,
vec4_visitor::lower_attributes_to_hw_regs(), which replaces registers
of type ATTR in the instruction stream with the hardware registers
that store those attributes.  This logic will need to be common
between the vertex and geometry shaders.

Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
i965/vs: Generalize computation of array strides in preparation for GS.

Geometry shader inputs are arrays, but they use an unusual array
layout: instead of all array elements for a given geometry shader
input being stored consecutively, all geometry shader inputs are
interleaved into one giant array.  As a result, the array stride we
use to access geometry shader inputs must be equal to the size of the
input VUE, rather than the size of the array element.

This patch introduces a new virtual function,
vec4_visitor::compute_array_stride(), which will allow geometry shader
compilation to specialize the computation of array stride to account
for the unusual layout of geometry shader input arrays.  It also
renames the local variable that the ir_dereference_array visitor uses
to store the stride, to avoid confusion.

Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
i965/vs: Don't hardcode DEBUG_VS in generic vec4 code.

Since the vec4_visitor and vec4_generator classes are going to be
re-used for geometry shaders, we can't enable their debug
functionality based on (INTEL_DEBUG & DEBUG_VS) anymore.  Instead, add
a debug_flag boolean to these two classes, so that when they're
instantiated the caller can specify whether debug dumps are needed.

Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
!UPSTREAM ===== BEGIN rebase of Plombo's GS patches =====
draw/gs: fix allocation of buffer for GS output vertices

Before, it accounted for the size of the vertices but not the other fields
in the vertex_header struct, which caused memory corruption.
mesa: add EXT_geometry_shader4 and ARB_geometry_shader4 to extension list
mesa: account for geometry shader texture fetches in update_texture_state
glcpp: define extension macros for EXT/ARB_geometry_shader4
glsl: add builtins for EXT/ARB_geometry_shader4
glsl: add ir_emitvertex and ir_endprim instruction types

These correspond to the EmitVertex and EndPrimitive functions in GLSL.

v2 (Paul Berry <stereotype441@gmail.com>): Add stub implementations of
new pure visitor functions to i965's vec4_visitor and fs_visitor
classes.
glsl: lower gl_ClipDistanceIn to gl_ClipDistanceInMESA in lower_clip_distance

This corresponds to the lowering of gl_ClipDistance to gl_ClipDistanceMESA.
It converts the 2D array gl_ClipDistanceIn from EXT/ARB_geometry_shader4 to
a 1D array of vec4s, gl_ClipDistanceInMESA.