diff options
Diffstat (limited to 'llvm/lib')
| -rw-r--r-- | llvm/lib/Analysis/ValueTracking.cpp | 12 |
1 files changed, 12 insertions, 0 deletions
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp index 16dd3078160..78ec2201fd5 100644 --- a/llvm/lib/Analysis/ValueTracking.cpp +++ b/llvm/lib/Analysis/ValueTracking.cpp @@ -1240,6 +1240,18 @@ static void computeKnownBitsFromOperator(Operator *I, APInt &KnownZero, KnownZero = APInt::getLowBitsSet(BitWidth, std::min(KnownZero2.countTrailingOnes(), KnownZero3.countTrailingOnes())); + + // If the operation is an addition that can't have signed overflow, + // then the sign bit is known to be zero if both input sign bits + // are zero. Similar for two negative inputs. + if (Opcode == Instruction::Add && + cast<OverflowingBinaryOperator>(LU)->hasNoSignedWrap()) { + if (KnownZero2.isNegative() && KnownZero3.isNegative()) + KnownZero.setBit(BitWidth-1); + if (KnownOne2.isNegative() && KnownOne3.isNegative()) + KnownOne.setBit(BitWidth-1); + } + break; } } |
