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[InstCombine] Simplify select if it combinated and/or/xor #73362

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Apr 3, 2024
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[InstCombine] Simplify select if it combinated and/or/xor #73362

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07479dd
[InstCombine] Add test for simplify select if it combinated and/or/xor
ParkHanbum Nov 27, 2023
3ae57ad
[InstCombine] Simplify select if it combinated `and/or/xor` (#71792)
ParkHanbum Nov 23, 2023
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106 changes: 106 additions & 0 deletions llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1687,6 +1687,109 @@ static Value *foldSelectInstWithICmpConst(SelectInst &SI, ICmpInst *ICI,
return nullptr;
}

static Instruction *foldSelectICmpEq(SelectInst &SI, ICmpInst *ICI,
InstCombinerImpl &IC) {
ICmpInst::Predicate Pred = ICI->getPredicate();
if (!ICmpInst::isEquality(Pred))
return nullptr;

Value *TrueVal = SI.getTrueValue();
Value *FalseVal = SI.getFalseValue();
Value *CmpLHS = ICI->getOperand(0);
Value *CmpRHS = ICI->getOperand(1);

if (Pred == ICmpInst::ICMP_NE)
std::swap(TrueVal, FalseVal);

// Transform (X == C) ? X : Y -> (X == C) ? C : Y
// specific handling for Bitwise operation.
// x&y -> (x|y) ^ (x^y) or (x|y) & ~(x^y)
// x|y -> (x&y) | (x^y) or (x&y) ^ (x^y)
// x^y -> (x|y) ^ (x&y) or (x|y) & ~(x&y)
Value *X, *Y;
if (!match(CmpLHS, m_BitwiseLogic(m_Value(X), m_Value(Y))) ||
!match(TrueVal, m_c_BitwiseLogic(m_Specific(X), m_Specific(Y))))
return nullptr;

const unsigned AndOps = Instruction::And, OrOps = Instruction::Or,
XorOps = Instruction::Xor, NoOps = 0;
enum NotMask { None = 0, NotInner, NotRHS };

auto matchFalseVal = [&](unsigned OuterOpc, unsigned InnerOpc,
unsigned NotMask) {
auto matchInner = m_c_BinOp(InnerOpc, m_Specific(X), m_Specific(Y));
if (OuterOpc == NoOps)
return match(CmpRHS, m_Zero()) && match(FalseVal, matchInner);

if (NotMask == NotInner) {
return match(FalseVal,
m_c_BinOp(OuterOpc, m_Not(matchInner), m_Specific(CmpRHS)));
} else if (NotMask == NotRHS) {
return match(FalseVal,
m_c_BinOp(OuterOpc, matchInner, m_Not(m_Specific(CmpRHS))));
} else {
return match(FalseVal,
m_c_BinOp(OuterOpc, matchInner, m_Specific(CmpRHS)));
}
};

// (X&Y)==C ? X|Y : X^Y -> (X^Y)|C : X^Y or (X^Y)^ C : X^Y
// (X&Y)==C ? X^Y : X|Y -> (X|Y)^C : X|Y or (X|Y)&~C : X|Y
if (match(CmpLHS, m_And(m_Value(X), m_Value(Y)))) {
if (match(TrueVal, m_c_Or(m_Specific(X), m_Specific(Y)))) {
// (X&Y)==C ? X|Y : (X^Y)|C -> (X^Y)|C : (X^Y)|C -> (X^Y)|C
// (X&Y)==C ? X|Y : (X^Y)^C -> (X^Y)^C : (X^Y)^C -> (X^Y)^C
if (matchFalseVal(OrOps, XorOps, None) ||
matchFalseVal(XorOps, XorOps, None))
return IC.replaceInstUsesWith(SI, FalseVal);
} else if (match(TrueVal, m_c_Xor(m_Specific(X), m_Specific(Y)))) {
// (X&Y)==C ? X^Y : (X|Y)^ C -> (X|Y)^ C : (X|Y)^ C -> (X|Y)^ C
// (X&Y)==C ? X^Y : (X|Y)&~C -> (X|Y)&~C : (X|Y)&~C -> (X|Y)&~C
if (matchFalseVal(XorOps, OrOps, None) ||
matchFalseVal(AndOps, OrOps, NotRHS))
return IC.replaceInstUsesWith(SI, FalseVal);
}
}

// (X|Y)==C ? X&Y : X^Y -> (X^Y)^C : X^Y or ~(X^Y)&C : X^Y
// (X|Y)==C ? X^Y : X&Y -> (X&Y)^C : X&Y or ~(X&Y)&C : X&Y
if (match(CmpLHS, m_Or(m_Value(X), m_Value(Y)))) {
if (match(TrueVal, m_c_And(m_Specific(X), m_Specific(Y)))) {
// (X|Y)==C ? X&Y: (X^Y)^C -> (X^Y)^C: (X^Y)^C -> (X^Y)^C
// (X|Y)==C ? X&Y:~(X^Y)&C ->~(X^Y)&C:~(X^Y)&C -> ~(X^Y)&C
if (matchFalseVal(XorOps, XorOps, None) ||
matchFalseVal(AndOps, XorOps, NotInner))
return IC.replaceInstUsesWith(SI, FalseVal);
} else if (match(TrueVal, m_c_Xor(m_Specific(X), m_Specific(Y)))) {
// (X|Y)==C ? X^Y : (X&Y)^C -> (X&Y)^C : (X&Y)^C -> (X&Y)^C
// (X|Y)==C ? X^Y :~(X&Y)&C -> ~(X&Y)&C :~(X&Y)&C -> ~(X&Y)&C
if (matchFalseVal(XorOps, AndOps, None) ||
matchFalseVal(AndOps, AndOps, NotInner))
return IC.replaceInstUsesWith(SI, FalseVal);
}
}

// (X^Y)==C ? X&Y : X|Y -> (X|Y)^C : X|Y or (X|Y)&~C : X|Y
// (X^Y)==C ? X|Y : X&Y -> (X&Y)|C : X&Y or (X&Y)^ C : X&Y
if (match(CmpLHS, m_Xor(m_Value(X), m_Value(Y)))) {
if ((match(TrueVal, m_c_And(m_Specific(X), m_Specific(Y))))) {
// (X^Y)==C ? X&Y : (X|Y)^C -> (X|Y)^C
// (X^Y)==C ? X&Y : (X|Y)&~C -> (X|Y)&~C
if (matchFalseVal(XorOps, OrOps, None) ||
matchFalseVal(AndOps, OrOps, NotRHS))
return IC.replaceInstUsesWith(SI, FalseVal);
} else if (match(TrueVal, m_c_Or(m_Specific(X), m_Specific(Y)))) {
// (X^Y)==C ? (X|Y) : (X&Y)|C -> (X&Y)|C
// (X^Y)==C ? (X|Y) : (X&Y)^C -> (X&Y)^C
if (matchFalseVal(OrOps, AndOps, None) ||
matchFalseVal(XorOps, AndOps, None))
return IC.replaceInstUsesWith(SI, FalseVal);
}
}

return nullptr;
}

/// Visit a SelectInst that has an ICmpInst as its first operand.
Instruction *InstCombinerImpl::foldSelectInstWithICmp(SelectInst &SI,
ICmpInst *ICI) {
Expand Down Expand Up @@ -1729,6 +1832,9 @@ Instruction *InstCombinerImpl::foldSelectInstWithICmp(SelectInst &SI,
}
}

if (Instruction *NewSel = foldSelectICmpEq(SI, ICI, *this))
return NewSel;

// Canonicalize a signbit condition to use zero constant by swapping:
// (CmpLHS > -1) ? TV : FV --> (CmpLHS < 0) ? FV : TV
// To avoid conflicts (infinite loops) with other canonicalizations, this is
Expand Down
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