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
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