[Mesa-dev] [PATCH] i965/fs: Drop no-op shifts by 0.

[Eric Anholt]

I noticed this in a shader in Unigine Heaven that was spilling.  While it
doesn't really reduce register pressure, it shaves a few instructions
anyway (7955 -> 7882).
---
 src/glsl/opt_algebraic.cpp | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/glsl/opt_algebraic.cpp b/src/glsl/opt_algebraic.cpp
index 37b2f02..ff06cfc 100644
--- a/src/glsl/opt_algebraic.cpp
+++ b/src/glsl/opt_algebraic.cpp
@@ -387,6 +387,14 @@ ir_algebraic_visitor::handle_expression(ir_expression *ir)
       }
       break;
 
+   case ir_binop_rshift:
+   case ir_binop_lshift:
+      if (is_vec_zero(op_const[0]))
+         return ir->operands[1];
+      else if (is_vec_zero(op_const[1]))
+         return ir->operands[0];
+      break;
+
    case ir_binop_logic_and:
       /* FINISHME: Also simplify (a && a) to (a). */
       if (is_vec_one(op_const[0])) {
-- 
1.8.4.rc3