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[InstCombine] foldSelectRotate - canonicalize to OR(SHL,LSHR). NFCI.

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Match the canonicalization code that was added to matchFunnelShift at rG02295e6d1a15
This commit is contained in:
Simon Pilgrim 2020-10-16 13:18:31 +01:00
parent 2528c4c3da
commit 6f0e70a2de
1 changed files with 14 additions and 11 deletions
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25
lib/Transforms/InstCombine/InstCombineSelect.cpp
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@ -2337,8 +2337,8 @@ static Instruction *factorizeMinMaxTree(SelectPatternFlavor SPF, Value *LHS,
static Instruction *foldSelectRotate(SelectInst &Sel,
InstCombiner::BuilderTy &Builder) {
// The false value of the select must be a rotate of the true value.
Value *Or0, *Or1;
if (!match(Sel.getFalseValue(), m_OneUse(m_Or(m_Value(Or0), m_Value(Or1)))))
BinaryOperator *Or0, *Or1;
if (!match(Sel.getFalseValue(), m_OneUse(m_Or(m_BinOp(Or0), m_BinOp(Or1)))))
return nullptr;
Value *TVal = Sel.getTrueValue();
@ -2346,16 +2346,20 @@ static Instruction *foldSelectRotate(SelectInst &Sel,
if (!match(Or0, m_OneUse(m_LogicalShift(m_Specific(TVal),
m_ZExtOrSelf(m_Value(SA0))))) ||
!match(Or1, m_OneUse(m_LogicalShift(m_Specific(TVal),
m_ZExtOrSelf(m_Value(SA1))))))
m_ZExtOrSelf(m_Value(SA1))))) ||
Or0->getOpcode() == Or1->getOpcode())
return nullptr;
auto ShiftOpcode0 = cast<BinaryOperator>(Or0)->getOpcode();
auto ShiftOpcode1 = cast<BinaryOperator>(Or1)->getOpcode();
if (ShiftOpcode0 == ShiftOpcode1)
return nullptr;
// Canonicalize to or(shl(TVal, SA0), lshr(TVal, SA1)).
if (Or0->getOpcode() == BinaryOperator::LShr) {
std::swap(Or0, Or1);
std::swap(SA0, SA1);
}
assert(Or0->getOpcode() == BinaryOperator::Shl &&
Or1->getOpcode() == BinaryOperator::LShr &&
"Illegal or(shift,shift) pair");
// We have one of these patterns so far:
// select ?, TVal, (or (lshr TVal, SA0), (shl TVal, SA1))
// We should now have this pattern:
// select ?, TVal, (or (shl TVal, SA0), (lshr TVal, SA1))
// This must be a power-of-2 rotate for a bitmasking transform to be valid.
unsigned Width = Sel.getType()->getScalarSizeInBits();
@ -2380,8 +2384,7 @@ static Instruction *foldSelectRotate(SelectInst &Sel,
// This is a rotate that avoids shift-by-bitwidth UB in a suboptimal way.
// Convert to funnel shift intrinsic.
bool IsFshl = (ShAmt == SA0 && ShiftOpcode0 == BinaryOperator::Shl) ||
(ShAmt == SA1 && ShiftOpcode1 == BinaryOperator::Shl);
bool IsFshl = (ShAmt == SA0);
Intrinsic::ID IID = IsFshl ? Intrinsic::fshl : Intrinsic::fshr;
Function *F = Intrinsic::getDeclaration(Sel.getModule(), IID, Sel.getType());
ShAmt = Builder.CreateZExt(ShAmt, Sel.getType());