Fix a crash in which a multiplication was being reported as being both negative
and positive: positive, because it could be directly computed to be positive;
negative, because the nsw flags means it is either negative or undefined (the
multiplication always overflowed).
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@145104 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp
index 9f7b5b5..22f1c14 100644
--- a/lib/Analysis/ValueTracking.cpp
+++ b/lib/Analysis/ValueTracking.cpp
@@ -248,9 +248,14 @@
APInt::getHighBitsSet(BitWidth, LeadZ);
KnownZero &= Mask;
- if (isKnownNonNegative)
+ // Only make use of no-wrap flags if we failed to compute the sign bit
+ // directly. This matters if the multiplication always overflows, in
+ // which case we prefer to follow the result of the direct computation,
+ // though as the program is invoking undefined behaviour we can choose
+ // whatever we like here.
+ if (isKnownNonNegative && !KnownOne.isNegative())
KnownZero.setBit(BitWidth - 1);
- else if (isKnownNegative)
+ else if (isKnownNegative && !KnownZero.isNegative())
KnownOne.setBit(BitWidth - 1);
return;