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[InstCombine] narrowRotate - 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 2020-10-14 16:42:08 +01:00
parent 55a70d8e91
commit 500c5cb174
1 changed files with 15 additions and 11 deletions
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26
lib/Transforms/InstCombine/InstCombineCasts.cpp
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@ -531,19 +531,25 @@ Instruction *InstCombinerImpl::narrowRotate(TruncInst &Trunc) {
// First, find an or'd pair of opposite shifts with the same shifted operand:
// trunc (or (lshr ShVal, ShAmt0), (shl ShVal, ShAmt1))
Value *Or0, *Or1;
if (!match(Trunc.getOperand(0), m_OneUse(m_Or(m_Value(Or0), m_Value(Or1)))))
BinaryOperator *Or0, *Or1;
if (!match(Trunc.getOperand(0), m_OneUse(m_Or(m_BinOp(Or0), m_BinOp(Or1)))))
return nullptr;
Value *ShVal, *ShAmt0, *ShAmt1;
if (!match(Or0, m_OneUse(m_LogicalShift(m_Value(ShVal), m_Value(ShAmt0)))) ||
!match(Or1, m_OneUse(m_LogicalShift(m_Specific(ShVal), m_Value(ShAmt1)))))
!match(Or1,
m_OneUse(m_LogicalShift(m_Specific(ShVal), m_Value(ShAmt1)))) ||
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(ShVal, ShAmt0), lshr(ShVal, ShAmt1)).
if (Or0->getOpcode() == BinaryOperator::LShr) {
std::swap(Or0, Or1);
std::swap(ShAmt0, ShAmt1);
}
assert(Or0->getOpcode() == BinaryOperator::Shl &&
Or1->getOpcode() == BinaryOperator::LShr &&
"Illegal or(shift,shift) pair");
// Match the shift amount operands for a rotate pattern. This always matches
// a subtraction on the R operand.
@ -570,10 +576,10 @@ Instruction *InstCombinerImpl::narrowRotate(TruncInst &Trunc) {
};
Value *ShAmt = matchShiftAmount(ShAmt0, ShAmt1, NarrowWidth);
bool SubIsOnLHS = false;
bool IsFshl = true; // Sub on LSHR.
if (!ShAmt) {
ShAmt = matchShiftAmount(ShAmt1, ShAmt0, NarrowWidth);
SubIsOnLHS = true;
IsFshl = false; // Sub on SHL.
}
if (!ShAmt)
return nullptr;
@ -591,8 +597,6 @@ Instruction *InstCombinerImpl::narrowRotate(TruncInst &Trunc) {
// llvm.fshl.i8(trunc(ShVal), trunc(ShVal), trunc(ShAmt))
Value *NarrowShAmt = Builder.CreateTrunc(ShAmt, DestTy);
Value *X = Builder.CreateTrunc(ShVal, DestTy);
bool IsFshl = (!SubIsOnLHS && ShiftOpcode0 == BinaryOperator::Shl) ||
(SubIsOnLHS && ShiftOpcode1 == BinaryOperator::Shl);
Intrinsic::ID IID = IsFshl ? Intrinsic::fshl : Intrinsic::fshr;
Function *F = Intrinsic::getDeclaration(Trunc.getModule(), IID, DestTy);
return IntrinsicInst::Create(F, { X, X, NarrowShAmt });