Mesa (master): st/glsl_to_tgsi: disable the merge registers pass conditionally

[Samuel Pitoiset]

Module: Mesa
Branch: master
Commit: 066a5729552925fc53e345b9e86a8699ba7ac451
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=066a5729552925fc53e345b9e86a8699ba7ac451

Author: Samuel Pitoiset <samuel.pitoiset at gmail.com>
Date:   Tue Apr 25 00:31:47 2017 +0200

st/glsl_to_tgsi: disable the merge registers pass conditionally

The main goal of this pass to merge temporary registers in order
to reduce the total number of registers and also to produce
optimal TGSI code.

In fact, compilers seem to be confused when temporary variables
are already merged, maybe because it's done too early in the
process.

Skipping the pass, reduce both the register pressure and the code
size, at least for Nouveau and RadeonSI because they have a real
backend compiler.

Found by luck while fixing an issue in the TGSI dead code elimination
pass which affects tex instructions with bindless samplers.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset at gmail.com>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle at amd.com>
Reviewed-by: Marek Olšák <marek.olsak at amd.com>

---

 src/mesa/state_tracker/st_glsl_to_tgsi.cpp | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
index de7fe7837a..8ca90f6c43 100644
--- a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
+++ b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
@@ -6639,6 +6639,7 @@ get_mesa_program_tgsi(struct gl_context *ctx,
          &ctx->Const.ShaderCompilerOptions[shader->Stage];
    struct pipe_screen *pscreen = ctx->st->pipe->screen;
    enum pipe_shader_type ptarget = st_shader_stage_to_ptarget(shader->Stage);
+   unsigned skip_merge_registers;
 
    validate_ir_tree(shader->ir);
 
@@ -6660,6 +6661,9 @@ get_mesa_program_tgsi(struct gl_context *ctx,
                                            PIPE_SHADER_CAP_TGSI_FMA_SUPPORTED);
    v->has_tex_txf_lz = pscreen->get_param(pscreen,
                                           PIPE_CAP_TGSI_TEX_TXF_LZ);
+   skip_merge_registers =
+      pscreen->get_shader_param(pscreen, ptarget,
+                                PIPE_SHADER_CAP_TGSI_SKIP_MERGE_REGISTERS);
 
    _mesa_generate_parameters_list_for_uniforms(shader_program, shader,
                                                prog->Parameters);
@@ -6712,7 +6716,8 @@ get_mesa_program_tgsi(struct gl_context *ctx,
    while (v->eliminate_dead_code());
 
    v->merge_two_dsts();
-   v->merge_registers();
+   if (!skip_merge_registers)
+      v->merge_registers();
    v->renumber_registers();
 
    /* Write the END instruction. */