Mesa (staging/19.2): glsl: replace 'x + (-x)' with constant 0
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Wed Sep 4 20:52:26 UTC 2019
Module: Mesa
Branch: staging/19.2
Commit: efa4aee99d918a0efaed798e7911f32f903cad23
URL: http://cgit.freedesktop.org/mesa/mesa/commit/?id=efa4aee99d918a0efaed798e7911f32f903cad23
Author: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer at amd.com>
Date: Wed Aug 28 10:56:52 2019 +0200
glsl: replace 'x + (-x)' with constant 0
This fixes a hang in shadertoy for radeonsi where a buffer was initialized with:
value -= value
with value being undefined.
In this case LLVM replace the operation with an assignment to NaN.
Cc: 19.1 19.2 <mesa-stable at lists.freedesktop.org>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=111241
Reviewed-by: Marek Olšák <marek.olsak at amd.com>
(cherry picked from commit 47cc660d9c19572e5ef2dce7c8ae1766a2ac9885)
---
src/compiler/glsl/opt_algebraic.cpp | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/src/compiler/glsl/opt_algebraic.cpp b/src/compiler/glsl/opt_algebraic.cpp
index ff4be269578..3147d25aea8 100644
--- a/src/compiler/glsl/opt_algebraic.cpp
+++ b/src/compiler/glsl/opt_algebraic.cpp
@@ -507,6 +507,18 @@ ir_algebraic_visitor::handle_expression(ir_expression *ir)
if (is_vec_zero(op_const[1]))
return ir->operands[0];
+ /* Replace (x + (-x)) with constant 0 */
+ for (int i = 0; i < 2; i++) {
+ if (op_expr[i]) {
+ if (op_expr[i]->operation == ir_unop_neg) {
+ ir_rvalue *other = ir->operands[(i + 1) % 2];
+ if (other && op_expr[i]->operands[0]->equals(other)) {
+ return ir_constant::zero(ir, ir->type);
+ }
+ }
+ }
+ }
+
/* Reassociate addition of constants so that we can do constant
* folding.
*/
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