[Mesa-dev] [PATCH 00/17] i965/vs: Generalize VS compiler back-end in preparation for GS.

[Paul Berry]

This patch series lays the groundwork for the i965 geometry shader
back-end by separating the functions and data structures which are
specific to vertex shaders from those that can also be used to compile
geometry shaders.  (Following a naming convention that is already
present in the codebase, this common code is referred to as "vec4"
code, since in the future we should be able to use it for any shader
stage where the hardware expects a pair of vec4s to be stored in each
register.  This includes tessellation control and tessellation
evaluation shaders.)

In particular, the following structs/classes have been split into a
base class containing vec4-generic data, and a derived class
containing VS-specific data:

- brw_vs_compile (new base struct is brw_vec4_compile)
- brw_vs_prog_key (new base struct is brw_vec4_prog_key)
- brw_vs_prog_data (new base struct is brw_vec4_prog_data)
- vec4_visitor (new derived class is vec4_vs_visitor)

In the case of vec4_visitor, standard C++ inheritance is used, and
VS-specific behaviours are moved into virtual functions.  The other
three cases use C-style inheritance (the derived struct has an
explicit "base" element, and there are no virtual functions), since
these structs need to be accessible from plain C code.

In addition, small modifications have been made to the vec4_generator
class and the brw_compute_vue_map() function to generalize them for
use by both vertex and geometry shaders.

To keep merge conflicts to a minimum (since this patch series has been
in development for several weeks), I've tried to minimize the amount
of code motion introduced by this change.  As a result, the patch
series leaves vec4_vs_visitor functions scattered in several files
(brw_vec4.cpp, brw_vec4_visitor.cpp, and brw_vec4_vp.cpp).  Once this
series lands, I'd like to follow up with a patch series that moves all
of the vec4_vs_visitor functions to a new brw_vec4_vs_visitor.cpp
file, and moves the class declaration to a corresponding header.  I'll
wait until this patch series has landed before starting on that, and
try not to do it while anyone is in the middle of major VS back-end
work.

Note that this patch series must be applied atop the patch "i965/vs:
Fix DEBUG_SHADER_TIME when VS terminates with 2 URB writes", which I
sent out for review this morning.  You can find the complete series in
context at branch "gs-backend-prep" of
git://github.com/stereotype441/mesa.git.

In order to verify that it's actually possible to build geometry
shader functionality atop these changes, I have begun prototyping an
implementation of geometry shaders which passes all existing geometry
shader Piglit tests.  (Sadly, there are many more tests left to write,
and features left to implement!)  I'll be sending out those patches in
the coming month(s), as they mature.  You can find that series in
branch "gs" of git://github.com/stereotype441/mesa.git.  Note that the
"gs" branch is *highly volatile*, so if you want to base work on it,
please let me know so we can coordinate.

Piglit-tested on i965/Gen7--no regressions.