[Mesa-dev] [PATCH 3/3] i965: Stop splitting fma() prior to optimization

[Jason Ekstrand]

According to the GLSL spec, if the user uses fma directly and you have it
in your hardware, you shouldn't split it.  For a while now, we've been
splitting all fma's up-front and then planned to fuse them later.  The only
reason why this possibly helped before was for ARB programs which is
handled by the previous commit. This fixes rendering corruptions in Tomb
Raider.

Shader-db results on Haswell:

   total instructions in shared programs: 7560300 -> 7561510 (0.02%)
   instructions in affected programs: 56265 -> 57475 (2.15%)
   helped: 86
   HURT: 291

The only shaders in the database that are affected are from Shadow of
Mordor which is the first app in our database to use fma().

Reported-by: Kenneth Graunke <kenneth at whitecape.org>
---
 src/mesa/drivers/dri/i965/brw_compiler.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/src/mesa/drivers/dri/i965/brw_compiler.c b/src/mesa/drivers/dri/i965/brw_compiler.c
index 0ea5e8b..7969543 100644
--- a/src/mesa/drivers/dri/i965/brw_compiler.c
+++ b/src/mesa/drivers/dri/i965/brw_compiler.c
@@ -72,7 +72,6 @@ shader_perf_log_mesa(void *data, const char *fmt, ...)
     * split all ffma instructions during opt_algebraic and we then re-combine \
     * them as a later step.                                                   \
     */                                                                        \
-   .lower_ffma = true,                                                        \
    .lower_sub = true,                                                         \
    .lower_fdiv = true,                                                        \
    .lower_scmp = true,                                                        \
-- 
2.5.0.400.gff86faf