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[InstCombine] Move the call to isSignBitCheck into getDemandedBitsLHSMask instead of calling it outside and passing its result through a flag. NFCI

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The result of the isSignBitCheck isn't used anywhere else and this allows us to share the m_APInt call in the likely case that it isn't a sign bit check.

llvm-svn: 314018
This commit is contained in:
Craig Topper 2017-09-22 18:57:23 +00:00
parent 5b35b68785
commit 3edda87c42
1 changed files with 8 additions and 15 deletions
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23
llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
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@ -3921,15 +3921,17 @@ static Instruction *processUMulZExtIdiom(ICmpInst &I, Value *MulVal,
/// When performing a comparison against a constant, it is possible that not all
/// the bits in the LHS are demanded. This helper method computes the mask that
/// IS demanded.
static APInt getDemandedBitsLHSMask(ICmpInst &I, unsigned BitWidth,
bool isSignCheck) {
if (isSignCheck)
return APInt::getSignMask(BitWidth);
static APInt getDemandedBitsLHSMask(ICmpInst &I, unsigned BitWidth) {
const APInt *RHS;
if (!match(I.getOperand(1), m_APInt(RHS)))
return APInt::getAllOnesValue(BitWidth);
// If this is a normal comparison, it demands all bits. If it is a sign bit
// comparison, it only demands the sign bit.
bool UnusedBit;
if (isSignBitCheck(I.getPredicate(), *RHS, UnusedBit))
return APInt::getSignMask(BitWidth);
switch (I.getPredicate()) {
// For a UGT comparison, we don't care about any bits that
// correspond to the trailing ones of the comparand. The value of these
@ -4115,20 +4117,11 @@ Instruction *InstCombiner::foldICmpUsingKnownBits(ICmpInst &I) {
if (!BitWidth)
return nullptr;
// If this is a normal comparison, it demands all bits. If it is a sign bit
// comparison, it only demands the sign bit.
bool IsSignBit = false;
const APInt *CmpC;
if (match(Op1, m_APInt(CmpC))) {
bool UnusedBit;
IsSignBit = isSignBitCheck(Pred, *CmpC, UnusedBit);
}
KnownBits Op0Known(BitWidth);
KnownBits Op1Known(BitWidth);
if (SimplifyDemandedBits(&I, 0,
getDemandedBitsLHSMask(I, BitWidth, IsSignBit),
getDemandedBitsLHSMask(I, BitWidth),
Op0Known, 0))
return &I;