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[ValueTracking] Prevent a call to computeKnownBits if we already know the state of the bit we would calculate. Also reuse a temporary APInt instead of creating a new one. 

llvm-svn: 300239
This commit is contained in:
Craig Topper 2017-04-13 19:04:45 +00:00
parent dcdb325fee
commit a80f2041f7
1 changed files with 8 additions and 7 deletions
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15
llvm/lib/Analysis/ValueTracking.cpp
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@ -918,13 +918,14 @@ static void computeKnownBitsFromOperator(const Operator *I, APInt &KnownZero,
// 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, Depth + 1, Q);
if (KnownOne3.countTrailingOnes() > 0)
if (!KnownZero[0] && !KnownOne[0] &&
(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))))) {
KnownZero2.clearAllBits(); KnownOne2.clearAllBits();
computeKnownBits(Y, KnownZero2, KnownOne2, Depth + 1, Q);
if (KnownOne2.countTrailingOnes() > 0)
KnownZero.setBit(0);
}
break;