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Teach value tracking to make use of flags in more situations. 

llvm-svn: 126642
This commit is contained in:
Nick Lewycky 2011-02-28 08:02:21 +00:00
parent 306f98c241
commit c9aab8567b
1 changed files with 25 additions and 0 deletions
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25
llvm/lib/Analysis/ValueTracking.cpp
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@ -696,6 +696,15 @@ bool llvm::isPowerOfTwo(Value *V, const TargetData *TD, unsigned Depth) {
return isPowerOfTwo(SI->getTrueValue(), TD, Depth) &&
isPowerOfTwo(SI->getFalseValue(), TD, Depth);
// An exact divide or right shift can only shift off zero bits, so the result
// is non-zero only if the first operand is non-zero.
if (match(V, m_Shr(m_Value(), m_Value())) ||
match(V, m_IDiv(m_Value(), m_Value()))) {
BinaryOperator *BO = cast<BinaryOperator>(V);
if (BO->isExact())
return isPowerOfTwo(BO->getOperand(0), TD, Depth);
}
return false;
}
@ -732,6 +741,11 @@ bool llvm::isKnownNonZero(Value *V, const TargetData *TD, unsigned Depth) {
// shl X, Y != 0 if X is odd. Note that the value of the shift is undefined
// if the lowest bit is shifted off the end.
if (BitWidth && match(V, m_Shl(m_Value(X), m_Value(Y)))) {
// shl nuw can't remove any non-zero bits.
BinaryOperator *BO = cast<BinaryOperator>(V);
if (BO->hasNoUnsignedWrap())
return isKnownNonZero(X, TD, Depth);
APInt KnownZero(BitWidth, 0);
APInt KnownOne(BitWidth, 0);
ComputeMaskedBits(X, APInt(BitWidth, 1), KnownZero, KnownOne, TD, Depth);
@ -741,11 +755,22 @@ bool llvm::isKnownNonZero(Value *V, const TargetData *TD, unsigned Depth) {
// shr X, Y != 0 if X is negative. Note that the value of the shift is not
// defined if the sign bit is shifted off the end.
else if (match(V, m_Shr(m_Value(X), m_Value(Y)))) {
// shr exact can only shift out zero bits.
BinaryOperator *BO = cast<BinaryOperator>(V);
if (BO->isExact())
return isKnownNonZero(X, TD, Depth);
bool XKnownNonNegative, XKnownNegative;
ComputeSignBit(X, XKnownNonNegative, XKnownNegative, TD, Depth);
if (XKnownNegative)
return true;
}
// div exact can only produce a zero if the dividend is zero.
else if (match(V, m_IDiv(m_Value(X), m_Value()))) {
BinaryOperator *BO = cast<BinaryOperator>(V);
if (BO->isExact())
return isKnownNonZero(X, TD, Depth);
}
// X + Y.
else if (match(V, m_Add(m_Value(X), m_Value(Y)))) {
bool XKnownNonNegative, XKnownNegative;