diff options
| author | Nick Lewycky <nicholas@mxc.ca> | 2011-03-11 09:00:19 +0000 |
|---|---|---|
| committer | Nick Lewycky <nicholas@mxc.ca> | 2011-03-11 09:00:19 +0000 |
| commit | b69050a94c1c9266ab048a79c8375e5b14d87c72 (patch) | |
| tree | bf7c5218182894c05403125a704ce60ba3aa5b18 /lib/Analysis/ValueTracking.cpp | |
| parent | 6fd2472b1b2d8f6a64b38874cbca95d3578e16a4 (diff) | |
Teach ComputeMaskedBits about nsw on add. I don't think there's anything we can
do with nuw here, but sub and mul should be given similar treatment.
Fixes PR9343 #15!
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@127463 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib/Analysis/ValueTracking.cpp')
| -rw-r--r-- | lib/Analysis/ValueTracking.cpp | 14 |
1 files changed, 14 insertions, 0 deletions
diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp index f05ad66b87..33fb1e8cdc 100644 --- a/lib/Analysis/ValueTracking.cpp +++ b/lib/Analysis/ValueTracking.cpp @@ -429,6 +429,20 @@ void llvm::ComputeMaskedBits(Value *V, const APInt &Mask, KnownZero |= LHSKnownZero & Mask; KnownOne |= LHSKnownOne & Mask; } + + // Are we still trying to solve for the sign bit? + if (Mask.isNegative() && !KnownZero.isNegative() && !KnownOne.isNegative()){ + OverflowingBinaryOperator *OBO = cast<OverflowingBinaryOperator>(I); + if (OBO->hasNoSignedWrap()) { + // Adding two positive numbers can't wrap into negative ... + if (LHSKnownZero.isNegative() && KnownZero2.isNegative()) + KnownZero |= APInt::getSignBit(BitWidth); + // and adding two negative numbers can't wrap into positive. + else if (LHSKnownOne.isNegative() && KnownOne2.isNegative()) + KnownOne |= APInt::getSignBit(BitWidth); + } + } + return; } case Instruction::SRem: |