[Mesa-dev] [RFC 3/3] i965/vec4: Use nir_move_vec_src_uses_to_dest

[Jason Ekstrand]

The idea here is not that it gives register coalescing a little bit of a
helping hand.  It doesn't actually fix the coalescing problems, but it
seems to help a good bit.

Shader-db results for vec4 programs on Haswell:

   total instructions in shared programs: 1801527 -> 1761720 (-2.21%)
   instructions in affected programs:     978662 -> 938855 (-4.07%)
   helped:                                7924
   HURT:                                  497

Shader-db results for GLSL IR vs. NIR vec4 on Haswell:

   total instructions in shared programs: 1853737 -> 1761720 (-4.96%)
   instructions in affected programs:     1686064 -> 1594047 (-5.46%)
   helped:                                7717
   HURT:                                  9942
---
 src/mesa/drivers/dri/i965/brw_nir.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/mesa/drivers/dri/i965/brw_nir.c b/src/mesa/drivers/dri/i965/brw_nir.c
index 8f3edc5..7a8e004 100644
--- a/src/mesa/drivers/dri/i965/brw_nir.c
+++ b/src/mesa/drivers/dri/i965/brw_nir.c
@@ -183,6 +183,11 @@ brw_create_nir(struct brw_context *brw,
       nir_print_shader(nir, stderr);
    }
 
+   if (!is_scalar) {
+      nir_move_vec_src_uses_to_dest(nir);
+      nir_validate_shader(nir);
+   }
+
    nir_convert_from_ssa(nir, is_scalar);
    nir_validate_shader(nir);
 
-- 
2.5.0.400.gff86faf