[Mesa-dev] [PATCH 23/74] glsl: Don't do constant propagation on buffer variables

[Iago Toral Quiroga]

Since the backing storage for these is shared we cannot ensure that the
value won't change by writes from other threads.
---
 src/glsl/opt_constant_propagation.cpp | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/glsl/opt_constant_propagation.cpp b/src/glsl/opt_constant_propagation.cpp
index 90cc0c8..0bb1f9f 100644
--- a/src/glsl/opt_constant_propagation.cpp
+++ b/src/glsl/opt_constant_propagation.cpp
@@ -444,6 +444,14 @@ ir_constant_propagation_visitor::add_constant(ir_assignment *ir)
    if (!deref->var->type->is_vector() && !deref->var->type->is_scalar())
       return;
 
+   /* We can't do copy propagation on buffer variables, since the underlying
+    * memory storage is shared across multiple threads we can't be sure that
+    * the variable value isn't modified between this assignment and the next
+    * instruction where its value is read.
+    */
+   if (deref->var->data.mode == ir_var_buffer)
+      return;
+
    entry = new(this->mem_ctx) acp_entry(deref->var, ir->write_mask, constant);
    this->acp->push_tail(entry);
 }
-- 
1.9.1