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@gmail.com>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>

diff --git a/src/mesa/state_tracker/st_glsl_to_tgsi.cpp b/src/mesa/state_tracker/st_glsl_to_tgsi.cpp
index de7fe7837a40551dca893cb00886880c7e6f0516..8ca90f6c43d89caf0911d1811a47b95ad624a139 100644 (file)
--- 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. */