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| author | Logan Chien <loganchien@google.com> | 2011-11-25 08:46:08 +0800 |
|---|---|---|
| committer | Logan Chien <loganchien@google.com> | 2011-11-25 13:43:44 +0800 |
| commit | 1429059dc0129c1cec938c29d6fce89e14293241 (patch) | |
| tree | ec4c55e5138c7eb9ad0313d4af895ad0c56d0978 /lib/Analysis/ValueTracking.cpp | |
| parent | 1035c3e84815607b4f8994cab03ae62cc8519a63 (diff) | |
| parent | 705f2431a086bbe662bca0035938e774378de3ec (diff) | |
| download | external_llvm-1429059dc0129c1cec938c29d6fce89e14293241.zip external_llvm-1429059dc0129c1cec938c29d6fce89e14293241.tar.gz external_llvm-1429059dc0129c1cec938c29d6fce89e14293241.tar.bz2 | |
Merge with LLVM upstream r145126 (Nov 25th 2011)
Change-Id: I30d08ae004a4c3c74092ad2537ab30cce4280e1d
Diffstat (limited to 'lib/Analysis/ValueTracking.cpp')
| -rw-r--r-- | lib/Analysis/ValueTracking.cpp | 9 |
1 files changed, 7 insertions, 2 deletions
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 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask, 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; |