i965/vs: Remove brw_vs_prog_data pointer from brw_vs_compile.

In patches that follow, we'll be splitting structs brw_vs_prog_data
and brw_vs_compile into a vec4-generic base struct and a VS-specific
derived struct (this will allow the vec4-generic code to be re-used
for geometry shaders).  Having brw_vs_compile point to
brw_vs_prog_data makes it difficult to do this cleanly.

Fortunately most of the functions that use brw_vs_compile (those in
the vec4_visitor class) already have access to brw_vs_prog_data
through a separate pointer (vec4_visitor::prog_data).  So all we have
to do is use that pointer consistently, and plumb prog_data through
the few remaining functions that need access to it.
i965/vs: split brw_vs_compile into generic and VS-specific parts.

This will allow the generic parts to be re-used for geometry shaders.
i965/vs: split brw_vs_prog_key into generic and VS-specific parts.

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