Mesa (master): glsl: Optimize (x + y cmp 0) into (x cmp -y).

[Matt Turner]

Module: Mesa
Branch: master
Commit: 34ec1a24d61f8b2f6ed58efa9fe7ea8cec917612
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=34ec1a24d61f8b2f6ed58efa9fe7ea8cec917612

Author: Matt Turner <mattst88 at gmail.com>
Date:   Sat Mar 29 12:31:24 2014 -0700

glsl: Optimize (x + y cmp 0) into (x cmp -y).

Cuts a small handful of instructions in Serious Sam 3:

instructions in affected programs:     4692 -> 4666 (-0.55%)

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

---

 src/glsl/opt_algebraic.cpp |   22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/src/glsl/opt_algebraic.cpp b/src/glsl/opt_algebraic.cpp
index 8494bd9..2db877d 100644
--- a/src/glsl/opt_algebraic.cpp
+++ b/src/glsl/opt_algebraic.cpp
@@ -445,6 +445,28 @@ ir_algebraic_visitor::handle_expression(ir_expression *ir)
       }
       break;
 
+   case ir_binop_less:
+   case ir_binop_lequal:
+   case ir_binop_greater:
+   case ir_binop_gequal:
+   case ir_binop_equal:
+   case ir_binop_nequal:
+      for (int add_pos = 0; add_pos < 2; add_pos++) {
+         ir_expression *add = op_expr[add_pos];
+
+         if (!add || add->operation != ir_binop_add)
+            continue;
+
+         ir_constant *zero = op_const[1 - add_pos];
+         if (!is_vec_zero(zero))
+            continue;
+
+         return new(mem_ctx) ir_expression(ir->operation,
+                                           add->operands[0],
+                                           neg(add->operands[1]));
+      }
+      break;
+
    case ir_binop_rshift:
    case ir_binop_lshift:
       /* 0 >> x == 0 */