Make LSR's OptimizeShadowIV ignore induction variables with negative
strides for now, because it doesn't handle them correctly. This fixes a
miscompile of SingleSource/Benchmarks/Misc-C++/ray.
This problem was usually hidden because indvars transforms such induction
variables into negations of canonical induction variables.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@85118 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/lib/Transforms/Scalar/LoopStrengthReduce.cpp
index 4c305aa..e20fb16 100644
--- a/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ b/lib/Transforms/Scalar/LoopStrengthReduce.cpp
@@ -2262,6 +2262,10 @@
if (!C) continue;
+ // Ignore negative constants, as the code below doesn't handle them
+ // correctly. TODO: Remove this restriction.
+ if (!C->getValue().isStrictlyPositive()) continue;
+
/* Add new PHINode. */
PHINode *NewPH = PHINode::Create(DestTy, "IV.S.", PH);