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nir: propagate known constant values into the if-then branch 

Helps Max Waves / VGPR use in a bunch of Unigine Heaven
shaders.

shader-db results radeonsi (VEGA):
Totals from affected shaders:
SGPRS: 5505440 -> 5505872 (0.01 %)
VGPRS: 3077520 -> 3077296 (-0.01 %)
Spilled SGPRs: 39032 -> 39030 (-0.01 %)
Spilled VGPRs: 16326 -> 16326 (0.00 %)
Private memory VGPRs: 0 -> 0 (0.00 %)
Scratch size: 744 -> 744 (0.00 %) dwords per thread
Code Size: 123755028 -> 123753316 (-0.00 %) bytes
Compile Time: 2751028 -> 2560786 (-6.92 %) milliseconds
LDS: 1415 -> 1415 (0.00 %) blocks
Max Waves: 972192 -> 972240 (0.00 %)
Wait states: 0 -> 0 (0.00 %)

vkpipeline-db results RADV (VEGA):

Totals from affected shaders:
SGPRS: 160 -> 160 (0.00 %)
VGPRS: 88 -> 88 (0.00 %)
Spilled SGPRs: 0 -> 0 (0.00 %)
Spilled VGPRs: 0 -> 0 (0.00 %)
Private memory VGPRs: 0 -> 0 (0.00 %)
Scratch size: 0 -> 0 (0.00 %) dwords per thread
Code Size: 18268 -> 18152 (-0.63 %) bytes
LDS: 0 -> 0 (0.00 %) blocks
Max Waves: 26 -> 26 (0.00 %)
Wait states: 0 -> 0 (0.00 %)

Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>
This commit is contained in:
Timothy Arceri 2018-11-23 11:49:19 +11:00
parent 250fffac15
commit 4218b6422c
1 changed files with 60 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

60
src/compiler/nir/nir_opt_if.c
View File

@ -1326,6 +1326,65 @@ opt_if_merge(nir_if *nif)
return progress;
}
/* Perform optimisations based on the values we can derive from the evaluation
* of if-statement conditions.
*/
static bool
opt_for_known_values(nir_builder *b, nir_if *nif)
{
bool progress = false;
assert(nif->condition.is_ssa);
nir_ssa_def *if_cond = nif->condition.ssa;
if (if_cond->parent_instr->type != nir_instr_type_alu)
return false;
nir_alu_instr *alu = nir_instr_as_alu(if_cond->parent_instr);
switch (alu->op) {
case nir_op_feq:
case nir_op_ieq: {
nir_load_const_instr *load_const = NULL;
nir_ssa_def *unknown_val = NULL;
nir_ssa_def *src0 = alu->src[0].src.ssa;
nir_ssa_def *src1 = alu->src[1].src.ssa;
if (src0->parent_instr->type == nir_instr_type_load_const) {
load_const = nir_instr_as_load_const(src0->parent_instr);
unknown_val = src1;
} else if (src1->parent_instr->type == nir_instr_type_load_const) {
load_const = nir_instr_as_load_const(src1->parent_instr);
unknown_val = src0;
}
if (!load_const)
return false;
/* TODO: remove this and support swizzles? */
if (unknown_val->num_components != 1)
return false;
/* Replace unknown ssa uses with the known constant */
nir_foreach_use_safe(use_src, unknown_val) {
nir_cursor cursor = nir_before_src(use_src, false);
nir_block *use_block = nir_cursor_current_block(cursor);
if (nir_block_dominates(nir_if_first_then_block(nif), use_block)) {
nir_instr_rewrite_src(use_src->parent_instr, use_src,
nir_src_for_ssa(&load_const->def));
progress = true;
}
}
break;
}
default:
return false;
}
return progress;
}
static bool
opt_if_cf_list(nir_builder *b, struct exec_list *cf_list)
{
@ -1380,6 +1439,7 @@ opt_if_safe_cf_list(nir_builder *b, struct exec_list *cf_list)
progress |= opt_if_safe_cf_list(b, &nif->then_list);
progress |= opt_if_safe_cf_list(b, &nif->else_list);
progress |= opt_if_evaluate_condition_use(b, nif);
progress |= opt_for_known_values(b, nif);
break;
}