[Mesa-stable] [PATCH 1/2] glsl: Don't copy propagate from SSBO or shared variables either

[Ian Romanick]

From: Ian Romanick <ian.d.romanick at intel.com>

Since SSBOs can be written, copy propagating a read can cause the
value to magically change.  SSBO reads are also very expensive, so
doing it twice will be slower.

Haswell, Broadwell, and Skylake had similar results. (Skylake shown)
total instructions in shared programs: 14399120 -> 14399119 (<.01%)
instructions in affected programs: 684 -> 683 (-0.15%)
helped: 1
HURT: 0

total cycles in shared programs: 532978931 -> 532973113 (<.01%)
cycles in affected programs: 530484 -> 524666 (-1.10%)
helped: 1
HURT: 0

Signed-off-by: Ian Romanick <ian.d.romanick at intel.com>
Cc: mesa-stable at lists.freedesktop.org
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=106774
---
 src/compiler/glsl/opt_copy_propagation.cpp | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/compiler/glsl/opt_copy_propagation.cpp b/src/compiler/glsl/opt_copy_propagation.cpp
index 6220aa86da9..206dffe4f1c 100644
--- a/src/compiler/glsl/opt_copy_propagation.cpp
+++ b/src/compiler/glsl/opt_copy_propagation.cpp
@@ -347,6 +347,8 @@ ir_copy_propagation_visitor::add_copy(ir_assignment *ir)
    if (lhs_var != NULL && rhs_var != NULL && lhs_var != rhs_var) {
       if (lhs_var->data.mode != ir_var_shader_storage &&
           lhs_var->data.mode != ir_var_shader_shared &&
+          rhs_var->data.mode != ir_var_shader_storage &&
+          rhs_var->data.mode != ir_var_shader_shared &&
           lhs_var->data.precise == rhs_var->data.precise) {
          _mesa_hash_table_insert(acp, lhs_var, rhs_var);
       }
-- 
2.14.4