diff options
Diffstat (limited to 'llvm/lib/Analysis')
| -rw-r--r-- | llvm/lib/Analysis/ValueTracking.cpp | 16 |
1 files changed, 16 insertions, 0 deletions
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp index abec5962266..8d39e4e542d 100644 --- a/llvm/lib/Analysis/ValueTracking.cpp +++ b/llvm/lib/Analysis/ValueTracking.cpp @@ -1077,6 +1077,22 @@ static void computeKnownBitsFromOperator(Operator *I, APInt &KnownZero, KnownOne &= KnownOne2; // Output known-0 are known to be clear if zero in either the LHS | RHS. KnownZero |= KnownZero2; + + // and(x, add (x, -1)) is a common idiom that always clears the low bit; + // here we handle the more general case of adding any odd number by + // matching the form add(x, add(x, y)) where y is odd. + // TODO: This could be generalized to clearing any bit set in y where the + // following bit is known to be unset in y. + Value *Y = nullptr; + if (match(I->getOperand(0), m_Add(m_Specific(I->getOperand(1)), + m_Value(Y))) || + match(I->getOperand(1), m_Add(m_Specific(I->getOperand(0)), + m_Value(Y)))) { + APInt KnownZero3(BitWidth, 0), KnownOne3(BitWidth, 0); + computeKnownBits(Y, KnownZero3, KnownOne3, DL, Depth + 1, Q); + if (KnownOne3.countTrailingOnes() > 0) + KnownZero |= APInt::getLowBitsSet(BitWidth, 1); + } break; } case Instruction::Or: { |
