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[InstCombine] visitXor - refactor ((X^C1)>>C2)^C3 -> (X>>C2)^((C1>>C2)^C3) fold. NFCI. 

This is still ConstantInt-only (scalar) but is refactored to use PatternMatch to make adding vector support in the future relatively trivial.
This commit is contained in:
Simon Pilgrim 2020-10-15 14:16:35 +01:00
parent b70cb50204
commit 09be7623e4
1 changed files with 16 additions and 26 deletions
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42
llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
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@ -3295,32 +3295,22 @@ Instruction *InstCombinerImpl::visitXor(BinaryOperator &I) {
}
// FIXME: This should not be limited to scalar (pull into APInt match above).
if (ConstantInt *RHSC = dyn_cast<ConstantInt>(Op1)) {
if (BinaryOperator *Op0I = dyn_cast<BinaryOperator>(Op0)) {
if (ConstantInt *Op0CI = dyn_cast<ConstantInt>(Op0I->getOperand(1))) {
if (Op0I->getOpcode() == Instruction::LShr) {
// ((X^C1) >> C2) ^ C3 -> (X>>C2) ^ ((C1>>C2)^C3)
// E1 = "X ^ C1"
BinaryOperator *E1;
ConstantInt *C1;
if (Op0I->hasOneUse() &&
(E1 = dyn_cast<BinaryOperator>(Op0I->getOperand(0))) &&
E1->getOpcode() == Instruction::Xor &&
(C1 = dyn_cast<ConstantInt>(E1->getOperand(1)))) {
// fold (C1 >> C2) ^ C3
ConstantInt *C2 = Op0CI, *C3 = RHSC;
APInt FoldConst = C1->getValue().lshr(C2->getValue());
FoldConst ^= C3->getValue();
// Prepare the two operands.
Value *Opnd0 = Builder.CreateLShr(E1->getOperand(0), C2);
Opnd0->takeName(Op0I);
cast<Instruction>(Opnd0)->setDebugLoc(I.getDebugLoc());
Value *FoldVal = ConstantInt::get(Ty, FoldConst);
return BinaryOperator::CreateXor(Opnd0, FoldVal);
}
}
}
{
Value *X;
ConstantInt *C1, *C2, *C3;
// ((X^C1) >> C2) ^ C3 -> (X>>C2) ^ ((C1>>C2)^C3)
if (match(Op1, m_ConstantInt(C3)) &&
match(Op0, m_LShr(m_Xor(m_Value(X), m_ConstantInt(C1)),
m_ConstantInt(C2))) &&
Op0->hasOneUse()) {
// fold (C1 >> C2) ^ C3
APInt FoldConst = C1->getValue().lshr(C2->getValue());
FoldConst ^= C3->getValue();
// Prepare the two operands.
auto *Opnd0 = cast<Instruction>(Builder.CreateLShr(X, C2));
Opnd0->takeName(cast<Instruction>(Op0));
Opnd0->setDebugLoc(I.getDebugLoc());
return BinaryOperator::CreateXor(Opnd0, ConstantInt::get(Ty, FoldConst));
}
}