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[InstCombine] Simplify select if it combinated and/or/xor (#71792)
`and/or/xor` operations can each be changed to sum of logical operations including operators other than themselves. `x&y -> (x|y) ^ (x^y)` `x|y -> (x&y) | (x^y)` `x^y -> (x|y) ^ (x&y)` if left of condition of `SelectInst` is `and/or/xor` logical operation and right is equal to `0, -1`, or a `constant`, and if `TrueVal` consist of `and/or/xor` logical operation then we can optimize this case. This patch implements this combination. Proof: https://alive2.llvm.org/ce/z/WW8iRR
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‎llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp

Lines changed: 117 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1687,6 +1687,120 @@ static Value *foldSelectInstWithICmpConst(SelectInst &SI, ICmpInst *ICI,
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return nullptr;
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}
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static Instruction *foldSelectICmpEq(SelectInst &SI, ICmpInst *ICI,
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InstCombinerImpl &IC) {
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ICmpInst::Predicate Pred = ICI->getPredicate();
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if (!ICmpInst::isEquality(Pred))
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return nullptr;
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Value *TrueVal = SI.getTrueValue();
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Value *FalseVal = SI.getFalseValue();
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Value *CmpLHS = ICI->getOperand(0);
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Value *CmpRHS = ICI->getOperand(1);
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if (Pred == ICmpInst::ICMP_NE)
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std::swap(TrueVal, FalseVal);
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// Transform (X == C) ? X : Y -> (X == C) ? C : Y
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// specific handling for Bitwise operation.
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// https://alive2.llvm.org/ce/z/mW3eYR
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// x&y -> (x|y) ^ (x^y) or (x|y) & ~(x^y)
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// x|y -> (x&y) | (x^y) or (x&y) ^ (x^y)
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// x^y -> (x|y) ^ (x&y) or (x|y) & ~(x&y)
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Value *X, *Y;
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if (!(match(CmpLHS, m_BitwiseLogic(m_Value(X), m_Value(Y)))) ||
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!(match(TrueVal, m_c_BitwiseLogic(m_Specific(X), m_Specific(Y)))))
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return nullptr;
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Value *AllOnes = Constant::getAllOnesValue(TrueVal->getType());
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Value *Null = Constant::getNullValue(TrueVal->getType());
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Instruction *ISI = &cast<Instruction>(SI);
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const unsigned AndOps = Instruction::And, OrOps = Instruction::Or,
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XorOps = Instruction::Xor, NoOps = 0;
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enum NotMask { None = 0, NotInner, NotRHS };
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auto matchFalseVal = [&](unsigned OuterOpc, unsigned InnerOpc,
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unsigned NotMask) {
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auto matchInner = m_c_BinOp(InnerOpc, m_Specific(X), m_Specific(Y));
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if (OuterOpc == NoOps) {
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if (match(CmpRHS, m_Zero()))
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return match(FalseVal, matchInner);
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else
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return false;
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}
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if (NotMask == NotInner) {
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return match(FalseVal,
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m_c_BinOp(OuterOpc, m_Not(matchInner), m_Specific(CmpRHS)));
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} else if (NotMask == NotRHS) {
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return match(FalseVal,
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m_c_BinOp(OuterOpc, matchInner, m_Not(m_Specific(CmpRHS))));
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} else {
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return match(FalseVal,
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m_c_BinOp(OuterOpc, matchInner, m_Specific(CmpRHS)));
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}
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};
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// https://alive2.llvm.org/ce/z/rw7XWv
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// (X&Y)==C ? X|Y : X^Y -> (X^Y)|C : X^Y or (X^Y)^ C : X^Y
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// (X&Y)==C ? X^Y : X|Y -> (X|Y)^C : X|Y or (X|Y)&~C : X|Y
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if (match(CmpLHS, m_And(m_Value(X), m_Value(Y)))) {
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if (match(TrueVal, m_c_Or(m_Specific(X), m_Specific(Y)))) {
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// (X&Y)==C ? X|Y : (X^Y)|C -> (X^Y)|C : (X^Y)|C -> (X^Y)|C
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if (matchFalseVal(OrOps, XorOps, None) ||
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// (X&Y)==C ? X|Y : (X^Y)^C -> (X^Y)^C : (X^Y)^C -> (X^Y)^C
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matchFalseVal(XorOps, XorOps, None))
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return IC.replaceInstUsesWith(*ISI, FalseVal);
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} else if (match(TrueVal, m_c_Xor(m_Specific(X), m_Specific(Y)))) {
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// (X&Y)==C ? X^Y : (X|Y)^ C -> (X|Y)^ C : (X|Y)^ C -> (X|Y)^ C
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if (matchFalseVal(XorOps, OrOps, None) ||
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// (X&Y)==C ? X^Y : (X|Y)&~C -> (X|Y)&~C : (X|Y)&~C -> (X|Y)&~C
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matchFalseVal(AndOps, OrOps, NotRHS))
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return IC.replaceInstUsesWith(*ISI, FalseVal);
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}
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}
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// https://alive2.llvm.org/ce/z/5yaUzR
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// (X|Y)==C ? X&Y : X^Y -> (X^Y)^C : X^Y or ~(X^Y)&C : X^Y
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// (X|Y)==C ? X^Y : X&Y -> (X&Y)^C : X&Y or ~(X&Y)&C : X&Y
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if (match(CmpLHS, m_Or(m_Value(X), m_Value(Y)))) {
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if (match(TrueVal, m_c_And(m_Specific(X), m_Specific(Y)))) {
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// (X|Y)==C ? X&Y: (X^Y)^C -> (X^Y)^C: (X^Y)^C -> (X^Y)^C
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if (matchFalseVal(XorOps, XorOps, None) ||
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// (X|Y)==C ? X&Y:~(X^Y)&C ->~(X^Y)&C:~(X^Y)&C -> ~(X^Y)&C
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matchFalseVal(AndOps, XorOps, NotInner))
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return IC.replaceInstUsesWith(*ISI, FalseVal);
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} else if (match(TrueVal, m_c_Xor(m_Specific(X), m_Specific(Y)))) {
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// (X|Y)==C ? X^Y : (X&Y)^C -> (X&Y)^C : (X&Y)^C -> (X&Y)^C
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if (matchFalseVal(XorOps, AndOps, None) ||
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// (X|Y)==C ? X^Y :~(X&Y)&C -> ~(X&Y)&C :~(X&Y)&C -> ~(X&Y)&C
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matchFalseVal(AndOps, AndOps, NotInner))
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return IC.replaceInstUsesWith(*ISI, FalseVal);
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}
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}
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// https://alive2.llvm.org/ce/z/dA9Hy-
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// (X^Y)==C ? X&Y : X|Y -> (X|Y)^C : X|Y or (X|Y)&~C : X|Y
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// (X^Y)==C ? X|Y : X&Y -> (X&Y)|C : X&Y or (X&Y)^ C : X&Y
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if (match(CmpLHS, m_Xor(m_Value(X), m_Value(Y)))) {
1786+
if ((match(TrueVal, m_c_And(m_Specific(X), m_Specific(Y))))) {
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// (X^Y)==C ? X&Y : (X|Y)^C -> (X|Y)^C
1788+
if (matchFalseVal(XorOps, OrOps, None) ||
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// (X^Y)==C ? X&Y : (X|Y)&~C -> (X|Y)&~C
1790+
matchFalseVal(AndOps, OrOps, NotRHS))
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return IC.replaceInstUsesWith(*ISI, FalseVal);
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} else if (match(TrueVal, m_c_Or(m_Specific(X), m_Specific(Y)))) {
1793+
// (X^Y)==C ? (X|Y) : (X&Y)|C -> (X&Y)|C
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if (matchFalseVal(OrOps, AndOps, None) ||
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// (X^Y)==C ? (X|Y) : (X&Y)^C -> (X&Y)^C
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matchFalseVal(XorOps, AndOps, None))
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return IC.replaceInstUsesWith(*ISI, FalseVal);
1798+
}
1799+
}
1800+
1801+
return nullptr;
1802+
}
1803+
16901804
/// Visit a SelectInst that has an ICmpInst as its first operand.
16911805
Instruction *InstCombinerImpl::foldSelectInstWithICmp(SelectInst &SI,
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ICmpInst *ICI) {
@@ -1729,6 +1843,9 @@ Instruction *InstCombinerImpl::foldSelectInstWithICmp(SelectInst &SI,
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}
17301844
}
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1846+
if (Instruction *NewSel = foldSelectICmpEq(SI, ICI, *this))
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return NewSel;
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// Canonicalize a signbit condition to use zero constant by swapping:
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// (CmpLHS > -1) ? TV : FV --> (CmpLHS < 0) ? FV : TV
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// To avoid conflicts (infinite loops) with other canonicalizations, this is

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