[Mesa-dev] [PATCH 2/3] ptn: Emit mul+add for MAD

[Jason Ekstrand]

Unlike fma() in GLSL, MAD in ARB programs is 100% splittable.  Just emit
the split version and let the optimizer fuse them later.

Shader-db results on Haswell:

   total instructions in shared programs: 7560379 -> 7560300 (-0.00%)
   instructions in affected programs: 143928 -> 143849 (-0.05%)
   helped: 443
   HURT: 250
---
 src/mesa/program/prog_to_nir.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/mesa/program/prog_to_nir.c b/src/mesa/program/prog_to_nir.c
index a6119ae..aa51dec 100644
--- a/src/mesa/program/prog_to_nir.c
+++ b/src/mesa/program/prog_to_nir.c
@@ -706,7 +706,7 @@ static const nir_op op_trans[MAX_OPCODE] = {
    [OPCODE_LIT] = 0,
    [OPCODE_LOG] = 0,
    [OPCODE_LRP] = 0,
-   [OPCODE_MAD] = nir_op_ffma,
+   [OPCODE_MAD] = 0,
    [OPCODE_MAX] = nir_op_fmax,
    [OPCODE_MIN] = nir_op_fmin,
    [OPCODE_MOV] = nir_op_fmov,
@@ -801,6 +801,10 @@ ptn_emit_instruction(struct ptn_compile *c, struct prog_instruction *prog_inst)
       ptn_lrp(b, dest, src);
       break;
 
+   case OPCODE_MAD:
+      ptn_move_dest(b, dest, nir_fadd(b, nir_fmul(b, src[0], src[1]), src[2]));
+      break;
+
    case OPCODE_DST:
       ptn_dst(b, dest, src);
       break;
-- 
2.5.0.400.gff86faf