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[InstCombine] clean up foldICmpXorConstant(); NFCI 

1. Change variable names
2. Use local variables to reduce code
3. Early exit to reduce indent

llvm-svn: 278955
This commit is contained in:
Sanjay Patel 2016-08-17 19:23:42 +00:00
parent 53ce3f9d02
commit 6d5f448746
1 changed files with 61 additions and 56 deletions
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117
llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
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@ -1569,73 +1569,78 @@ Instruction *InstCombiner::foldICmpTruncConstant(ICmpInst &ICI,
return nullptr;
}
Instruction *InstCombiner::foldICmpXorConstant(ICmpInst &ICI, Instruction *LHSI,
const APInt *RHSV) {
/// Fold icmp (xor X, Y), C.
Instruction *InstCombiner::foldICmpXorConstant(ICmpInst &Cmp, Instruction *Xor,
const APInt *C) {
// FIXME: This check restricts all folds under here to scalar types.
ConstantInt *RHS = dyn_cast<ConstantInt>(ICI.getOperand(1));
ConstantInt *RHS = dyn_cast<ConstantInt>(Cmp.getOperand(1));
if (!RHS)
return nullptr;
if (ConstantInt *XorCst = dyn_cast<ConstantInt>(LHSI->getOperand(1))) {
// If this is a comparison that tests the signbit (X < 0) or (x > -1),
// fold the xor.
if ((ICI.getPredicate() == ICmpInst::ICMP_SLT && *RHSV == 0) ||
(ICI.getPredicate() == ICmpInst::ICMP_SGT && RHSV->isAllOnesValue())) {
Value *CompareVal = LHSI->getOperand(0);
auto *XorCst = dyn_cast<ConstantInt>(Xor->getOperand(1));
if (!XorCst)
return nullptr;
// If the sign bit of the XorCst is not set, there is no change to
// the operation, just stop using the Xor.
if (!XorCst->isNegative()) {
ICI.setOperand(0, CompareVal);
Worklist.Add(LHSI);
return &ICI;
}
// If this is a comparison that tests the signbit (X < 0) or (x > -1),
// fold the xor.
ICmpInst::Predicate Pred = Cmp.getPredicate();
if ((Pred == ICmpInst::ICMP_SLT && *C == 0) ||
(Pred == ICmpInst::ICMP_SGT && C->isAllOnesValue())) {
Value *CompareVal = Xor->getOperand(0);
// Was the old condition true if the operand is positive?
bool isTrueIfPositive = ICI.getPredicate() == ICmpInst::ICMP_SGT;
// If so, the new one isn't.
isTrueIfPositive ^= true;
if (isTrueIfPositive)
return new ICmpInst(ICmpInst::ICMP_SGT, CompareVal, SubOne(RHS));
else
return new ICmpInst(ICmpInst::ICMP_SLT, CompareVal, AddOne(RHS));
// If the sign bit of the XorCst is not set, there is no change to
// the operation, just stop using the Xor.
if (!XorCst->isNegative()) {
Cmp.setOperand(0, CompareVal);
Worklist.Add(Xor);
return &Cmp;
}
if (LHSI->hasOneUse()) {
// (icmp u/s (xor A SignBit), C) -> (icmp s/u A, (xor C SignBit))
if (!ICI.isEquality() && XorCst->getValue().isSignBit()) {
const APInt &SignBit = XorCst->getValue();
ICmpInst::Predicate Pred = ICI.isSigned() ? ICI.getUnsignedPredicate()
: ICI.getSignedPredicate();
return new ICmpInst(Pred, LHSI->getOperand(0),
Builder->getInt(*RHSV ^ SignBit));
}
// Was the old condition true if the operand is positive?
bool isTrueIfPositive = Pred == ICmpInst::ICMP_SGT;
// (icmp u/s (xor A ~SignBit), C) -> (icmp s/u (xor C ~SignBit), A)
if (!ICI.isEquality() && XorCst->isMaxValue(true)) {
const APInt &NotSignBit = XorCst->getValue();
ICmpInst::Predicate Pred = ICI.isSigned() ? ICI.getUnsignedPredicate()
: ICI.getSignedPredicate();
Pred = ICI.getSwappedPredicate(Pred);
return new ICmpInst(Pred, LHSI->getOperand(0),
Builder->getInt(*RHSV ^ NotSignBit));
}
}
// If so, the new one isn't.
isTrueIfPositive ^= true;
// (icmp ugt (xor X, C), ~C) -> (icmp ult X, C)
// iff -C is a power of 2
if (ICI.getPredicate() == ICmpInst::ICMP_UGT &&
XorCst->getValue() == ~(*RHSV) && (*RHSV + 1).isPowerOf2())
return new ICmpInst(ICmpInst::ICMP_ULT, LHSI->getOperand(0), XorCst);
// (icmp ult (xor X, C), -C) -> (icmp uge X, C)
// iff -C is a power of 2
if (ICI.getPredicate() == ICmpInst::ICMP_ULT &&
XorCst->getValue() == -(*RHSV) && RHSV->isPowerOf2())
return new ICmpInst(ICmpInst::ICMP_UGE, LHSI->getOperand(0), XorCst);
if (isTrueIfPositive)
return new ICmpInst(ICmpInst::ICMP_SGT, CompareVal, SubOne(RHS));
else
return new ICmpInst(ICmpInst::ICMP_SLT, CompareVal, AddOne(RHS));
}
if (Xor->hasOneUse()) {
// (icmp u/s (xor A SignBit), C) -> (icmp s/u A, (xor C SignBit))
if (!Cmp.isEquality() && XorCst->getValue().isSignBit()) {
const APInt &SignBit = XorCst->getValue();
ICmpInst::Predicate Pred = Cmp.isSigned() ? Cmp.getUnsignedPredicate()
: Cmp.getSignedPredicate();
return new ICmpInst(Pred, Xor->getOperand(0),
Builder->getInt(*C ^ SignBit));
}
// (icmp u/s (xor A ~SignBit), C) -> (icmp s/u (xor C ~SignBit), A)
if (!Cmp.isEquality() && XorCst->isMaxValue(true)) {
const APInt &NotSignBit = XorCst->getValue();
ICmpInst::Predicate Pred = Cmp.isSigned() ? Cmp.getUnsignedPredicate()
: Cmp.getSignedPredicate();
Pred = Cmp.getSwappedPredicate(Pred);
return new ICmpInst(Pred, Xor->getOperand(0),
Builder->getInt(*C ^ NotSignBit));
}
}
// (icmp ugt (xor X, C), ~C) -> (icmp ult X, C)
// iff -C is a power of 2
if (Pred == ICmpInst::ICMP_UGT && XorCst->getValue() == ~(*C) &&
(*C + 1).isPowerOf2())
return new ICmpInst(ICmpInst::ICMP_ULT, Xor->getOperand(0), XorCst);
// (icmp ult (xor X, C), -C) -> (icmp uge X, C)
// iff -C is a power of 2
if (Pred == ICmpInst::ICMP_ULT && XorCst->getValue() == -(*C) &&
C->isPowerOf2())
return new ICmpInst(ICmpInst::ICMP_UGE, Xor->getOperand(0), XorCst);
return nullptr;
}