[InstCombine] allow flag propagation when using safe constant
This corresponds with the code for the single binop pattern
added in rL336684.
llvm-svn: 336696
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp b/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
index 8fecd69..2560feb 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
@@ -1339,12 +1339,13 @@
// Flags are intersected from the 2 source binops. But there are 2 exceptions:
// 1. If we changed an opcode, poison conditions might have changed.
// 2. If the shuffle had undef mask elements, the new binop might have undefs
- // where the original code did not. Drop all poison potential to be safe.
+ // where the original code did not. But if we already made a safe constant,
+ // then there's no danger.
NewBO->copyIRFlags(B0);
NewBO->andIRFlags(B1);
if (DropNSW)
NewBO->setHasNoSignedWrap(false);
- if (Mask->containsUndefElement())
+ if (Mask->containsUndefElement() && !MightCreatePoisonOrUB)
NewBO->dropPoisonGeneratingFlags();
return NewBO;
}