[Mesa-dev] [PATCH 09/10] glsl: Optimize A - neg(B) == A + B

[thomashelland90 at gmail.com]

From: Thomas Helland <thomashelland90 at gmail.com>

...and  neg(A) - B == neg(A + B)

Signed-off-by: Thomas Helland <thomashelland90 at gmail.com>
---
 src/glsl/opt_algebraic.cpp | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/glsl/opt_algebraic.cpp b/src/glsl/opt_algebraic.cpp
index 2361d0f..fba9de6 100644
--- a/src/glsl/opt_algebraic.cpp
+++ b/src/glsl/opt_algebraic.cpp
@@ -454,6 +454,12 @@ ir_algebraic_visitor::handle_expression(ir_expression *ir)
       /* X - X == 0 */
       if (ir->operands[0]->equals(ir->operands[1]))
          return ir_constant::zero(ir, ir->type);
+      /* A - neg(B) = A + B */
+      if (op_expr[1] && op_expr[1]->operation == ir_unop_neg)
+         return add(ir->operands[0], op_expr[1]->operands[0]);
+      /* neg(A) - B = neg(A + B) */
+      if (op_expr[0] && op_expr[0]->operation == ir_unop_neg)
+         return neg(add(op_expr[0]->operands[0], ir->operands[1]));
       break;
 
    case ir_binop_mul:
-- 
2.0.0