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authorEduardo Lima Mitev <[email protected]>2015-10-22 15:32:13 +0200
committerEduardo Lima Mitev <[email protected]>2015-11-10 21:13:35 +0100
commitde51676b410ff3ccab1df765f8eee15126c9de4c (patch)
tree020e81651d7307d8f7f13e4a11cc6c96614f995f /src/mesa
parentfb3b5669cee85781b603f612228387e9a2e4120f (diff)
i965/nir/opt_peephole_ffma: Bypass fusion if any operand of fadd and fmul is a const
When both fadd and fmul instructions have at least one operand that is a constant and it is only used once, the total number of instructions can be reduced from 3 (1 ffma + 2 load_const) to 2 (1 fmul + 1 fadd); because the constants will be progagated as immediate operands of fmul and fadd. This patch detects these situations and prevents fusing fmul+fadd into ffma. Shader-db results on i965 Haswell: total instructions in shared programs: 6235835 -> 6225895 (-0.16%) instructions in affected programs: 1124094 -> 1114154 (-0.88%) total loops in shared programs: 1979 -> 1979 (0.00%) helped: 7612 HURT: 843 GAINED: 4 LOST: 0 Reviewed-by: Jason Ekstrand <[email protected]>
Diffstat (limited to 'src/mesa')
-rw-r--r--src/mesa/drivers/dri/i965/brw_nir_opt_peephole_ffma.c31
1 files changed, 31 insertions, 0 deletions
diff --git a/src/mesa/drivers/dri/i965/brw_nir_opt_peephole_ffma.c b/src/mesa/drivers/dri/i965/brw_nir_opt_peephole_ffma.c
index a8448e73a3f..5603129bde7 100644
--- a/src/mesa/drivers/dri/i965/brw_nir_opt_peephole_ffma.c
+++ b/src/mesa/drivers/dri/i965/brw_nir_opt_peephole_ffma.c
@@ -133,6 +133,28 @@ get_mul_for_src(nir_alu_src *src, int num_components,
return alu;
}
+/**
+ * Given a list of (at least two) nir_alu_src's, tells if any of them is a
+ * constant value and is used only once.
+ */
+static bool
+any_alu_src_is_a_constant(nir_alu_src srcs[])
+{
+ for (unsigned i = 0; i < 2; i++) {
+ if (srcs[i].src.ssa->parent_instr->type == nir_instr_type_load_const) {
+ nir_load_const_instr *load_const =
+ nir_instr_as_load_const (srcs[i].src.ssa->parent_instr);
+
+ if (list_is_singular(&load_const->def.uses) &&
+ list_empty(&load_const->def.if_uses)) {
+ return true;
+ }
+ }
+ }
+
+ return false;
+}
+
static bool
brw_nir_opt_peephole_ffma_block(nir_block *block, void *void_state)
{
@@ -183,6 +205,15 @@ brw_nir_opt_peephole_ffma_block(nir_block *block, void *void_state)
mul_src[0] = mul->src[0].src.ssa;
mul_src[1] = mul->src[1].src.ssa;
+ /* If any of the operands of the fmul and any of the fadd is a constant,
+ * we bypass because it will be more efficient as the constants will be
+ * propagated as operands, potentially saving two load_const instructions.
+ */
+ if (any_alu_src_is_a_constant(mul->src) &&
+ any_alu_src_is_a_constant(add->src)) {
+ continue;
+ }
+
if (abs) {
for (unsigned i = 0; i < 2; i++) {
nir_alu_instr *abs = nir_alu_instr_create(state->mem_ctx,