Mesa (master): glsl: Optimize lrp(x, 0, a) into x - (x * a).

[Matt Turner]

Module: Mesa
Branch: master
Commit: d5fa8a956211692441b9c3ffc97b7486599ab3a3
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=d5fa8a956211692441b9c3ffc97b7486599ab3a3

Author: Matt Turner <mattst88 at gmail.com>
Date:   Mon Feb 24 15:00:45 2014 -0800

glsl: Optimize lrp(x, 0, a) into x - (x * a).

Helps one program in shader-db:

instructions in affected programs:     96 -> 92 (-4.17%)

Reviewed-by: Ian Romanick <ian.d.romanick at intel.com>

---

 src/glsl/opt_algebraic.cpp |    2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/glsl/opt_algebraic.cpp b/src/glsl/opt_algebraic.cpp
index 28f95a4..778638c 100644
--- a/src/glsl/opt_algebraic.cpp
+++ b/src/glsl/opt_algebraic.cpp
@@ -570,6 +570,8 @@ ir_algebraic_visitor::handle_expression(ir_expression *ir)
          return ir->operands[0];
       } else if (is_vec_zero(op_const[0])) {
          return mul(ir->operands[1], ir->operands[2]);
+      } else if (is_vec_zero(op_const[1])) {
+         return add(ir->operands[0], neg(mul(ir->operands[0], ir->operands[2])));
       }
       break;