intel/vec4: Allow late copy propagation on vec4

This change incurs a small amount of hurt now, but it enables a lot of
benefit on vec4 shaders on the next commit.  nir_opt_algebraic_late
converts dph, dot3, etc. to dhp_replicated, dot_replicated3, etc.  In
the process, it introduces extra moves.  If the original NIR contained

        vec1 32 ssa_45 = fdot4 ssa_51, ssa_44
        vec1 32 ssa_46 = fneg ssa_45

nir_opt_algebraic_late will produce

        vec4 32 ssa_18 = fdot_replicated4 ssa_1, ssa_15
        vec1 32 ssa_19 = mov ssa_18.x
        vec1 32 ssa_17 = fneg ssa_19

The algebraic pass added in the next commit can't see through the move
to know that the fneg applies to a fdot_replicated4.

Haswell, Ivy Bridge, and Sandybridge had similar results. (Haswell shown)
total cycles in shared programs: 187077604 -> 187079858 (<.01%)
cycles in affected programs: 350132 -> 352386 (0.64%)
helped: 174
HURT: 194
helped stats (abs) min: 2 max: 124 x̄: 23.60 x̃: 16
helped stats (rel) min: 0.12% max: 15.88% x̄: 4.98% x̃: 3.86%
HURT stats (abs)   min: 2 max: 164 x̄: 32.78 x̃: 16
HURT stats (rel)   min: 0.17% max: 22.82% x̄: 6.46% x̃: 0.86%
95% mean confidence interval for cycles value: 2.04 10.21
95% mean confidence interval for cycles %-change: 0.17% 1.93%
Cycles are HURT.

No shader-db changes on any other Intel platform.

Reviewed-by: Matt Turner <mattst88@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/1359>

diff --git a/src/intel/compiler/brw_nir.c b/src/intel/compiler/brw_nir.c
index 25395747c13d94cfe68914195b1ff90ea3d7708e..8c0be0d8a26f8473c4e6fe9f2e5e46fae6eae48c 100644 (file)
--- a/src/intel/compiler/brw_nir.c
+++ b/src/intel/compiler/brw_nir.c
@@ -907,10 +907,10 @@ brw_postprocess_nir(nir_shader *nir, const struct brw_compiler *compiler,
           * havok on the vec4 backend.  The handling of constants in the vec4
           * backend is not good.
           */
-         if (is_scalar) {
+         if (is_scalar)
             OPT(nir_opt_constant_folding);
-            OPT(nir_copy_prop);
-         }
+
+         OPT(nir_copy_prop);
          OPT(nir_opt_dce);
          OPT(nir_opt_cse);
       }