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[CodeGen] Teach DAG combine to fold select_cc seteq X, 0, sizeof(X), ctlz_zero_undef(X) -> ctlz(X). InstCombine already does this for IR and X86 pattern matches this during isel. 

A follow up commit will remove the X86 patterns to allow this to be tested.

llvm-svn: 267325
This commit is contained in:
Craig Topper 2016-04-24 04:38:32 +00:00
parent beb77bd89f
commit 36c133159a
1 changed files with 35 additions and 0 deletions
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35
llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
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@ -14349,6 +14349,41 @@ SDValue DAGCombiner::SimplifySelectCC(SDLoc DL, SDValue N0, SDValue N1,
}
}
// select_cc seteq X, 0, sizeof(X), ctlz(X) -> ctlz(X)
// select_cc seteq X, 0, sizeof(X), ctlz_zero_undef(X) -> ctlz(X)
// select_cc seteq X, 0, sizeof(X), cttz(X) -> cttz(X)
// select_cc seteq X, 0, sizeof(X), cttz_zero_undef(X) -> cttz(X)
// select_cc setne X, 0, ctlz(X), sizeof(X) -> ctlz(X)
// select_cc setne X, 0, ctlz_zero_undef(X), sizeof(X) -> ctlz(X)
// select_cc setne X, 0, cttz(X), sizeof(X) -> cttz(X)
// select_cc setne X, 0, cttz_zero_undef(X), sizeof(X) -> cttz(X)
if (N1C && N1C->isNullValue() && (CC == ISD::SETEQ || CC == ISD::SETNE)) {
SDValue ValueOnZero = N2;
SDValue Count = N3;
// If the condition is NE instead of E, swap the operands.
if (CC == ISD::SETNE)
std::swap(ValueOnZero, Count);
// Check if the value on zero is a constant equal to the bits in the type.
if (auto *ValueOnZeroC = dyn_cast<ConstantSDNode>(ValueOnZero)) {
if (ValueOnZeroC->getAPIntValue() == VT.getSizeInBits()) {
// If the other operand is cttz/cttz_zero_undef of N0, and cttz is
// legal, combine to just cttz.
if ((Count.getOpcode() == ISD::CTTZ ||
Count.getOpcode() == ISD::CTTZ_ZERO_UNDEF) &&
N0 == Count.getOperand(0) &&
(!LegalOperations || TLI.isOperationLegal(ISD::CTTZ, VT)))
return DAG.getNode(ISD::CTTZ, DL, VT, N0);
// If the other operand is ctlz/ctlz_zero_undef of N0, and ctlz is
// legal, combine to just ctlz.
if ((Count.getOpcode() == ISD::CTLZ ||
Count.getOpcode() == ISD::CTLZ_ZERO_UNDEF) &&
N0 == Count.getOperand(0) &&
(!LegalOperations || TLI.isOperationLegal(ISD::CTLZ, VT)))
return DAG.getNode(ISD::CTLZ, DL, VT, N0);
}
}
}
return SDValue();
}