[Mesa-dev] [PATCH] radv: call constant folding before opt algebraic

[Timothy Arceri]

The pattern of calling opt algebraic first seems to have originated
in i965. The order in OpenGL drivers generally doesn't matter
because the GLSL IR optimisations do constant folding before
opt algebraic.

However in Vulkan drivers calling opt algebraic first can result
in missed constant folding opportunities.

vkpipeline-db results (VEGA64):

Totals from affected shaders:
SGPRS: 3160 -> 3176 (0.51 %)
VGPRS: 3588 -> 3580 (-0.22 %)
Spilled SGPRs: 52 -> 44 (-15.38 %)
Spilled VGPRs: 0 -> 0 (0.00 %)
Private memory VGPRs: 0 -> 0 (0.00 %)
Scratch size: 12 -> 12 (0.00 %) dwords per thread
Code Size: 261812 -> 261036 (-0.30 %) bytes
LDS: 7 -> 7 (0.00 %) blocks
Max Waves: 346 -> 348 (0.58 %)
Wait states: 0 -> 0 (0.00 %)
---
 src/amd/vulkan/radv_shader.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/amd/vulkan/radv_shader.c b/src/amd/vulkan/radv_shader.c
index cd5a9f2afb4..ad7b2439735 100644
--- a/src/amd/vulkan/radv_shader.c
+++ b/src/amd/vulkan/radv_shader.c
@@ -162,8 +162,8 @@ radv_optimize_nir(struct nir_shader *shader, bool optimize_conservatively,
                 NIR_PASS(progress, shader, nir_opt_dead_cf);
                 NIR_PASS(progress, shader, nir_opt_cse);
                 NIR_PASS(progress, shader, nir_opt_peephole_select, 8, true, true);
-                NIR_PASS(progress, shader, nir_opt_algebraic);
                 NIR_PASS(progress, shader, nir_opt_constant_folding);
+                NIR_PASS(progress, shader, nir_opt_algebraic);
                 NIR_PASS(progress, shader, nir_opt_undef);
                 NIR_PASS(progress, shader, nir_opt_conditional_discard);
                 if (shader->options->max_unroll_iterations) {
-- 
2.20.1