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[x86] improve comments for SHRUNKBLEND node creation; NFC

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llvm-svn: 294344
This commit is contained in:
Sanjay Patel 2017-02-07 19:54:16 +00:00
parent df3b8cddb2
commit 704fe71950
2 changed files with 27 additions and 28 deletions
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49
lib/Target/X86/X86ISelLowering.cpp
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@ -29520,39 +29520,38 @@ static SDValue combineSelect(SDNode *N, SelectionDAG &DAG,
if (TLO.ShrinkDemandedConstant(Cond, DemandedMask) ||
TLI.SimplifyDemandedBits(Cond, DemandedMask, KnownZero, KnownOne,
TLO)) {
// If we changed the computation somewhere in the DAG, this change
// will affect all users of Cond.
// Make sure it is fine and update all the nodes so that we do not
// use the generic VSELECT anymore. Otherwise, we may perform
// wrong optimizations as we messed up with the actual expectation
// If we changed the computation somewhere in the DAG, this change will
// affect all users of Cond. Make sure it is fine and update all the nodes
// so that we do not use the generic VSELECT anymore. Otherwise, we may
// perform wrong optimizations as we messed with the actual expectation
// for the vector boolean values.
if (Cond != TLO.Old) {
// Check all uses of that condition operand to check whether it will be
// consumed by non-BLEND instructions, which may depend on all bits are
// set properly.
for (SDNode *U : Cond->uses())
// Check all uses of the condition operand to check whether it will be
// consumed by non-BLEND instructions. Those may require that all bits
// are set properly.
for (SDNode *U : Cond->uses()) {
// TODO: Add other opcodes eventually lowered into BLEND.
if (U->getOpcode() != ISD::VSELECT)
// TODO: Add other opcodes eventually lowered into BLEND.
return SDValue();
}
// Update all the users of the condition, before committing the change,
// so that the VSELECT optimizations that expect the correct vector
// boolean value will not be triggered.
for (SDNode *U : Cond->uses())
DAG.ReplaceAllUsesOfValueWith(
SDValue(U, 0),
DAG.getNode(X86ISD::SHRUNKBLEND, SDLoc(U), U->getValueType(0),
Cond, U->getOperand(1), U->getOperand(2)));
// Update all users of the condition before committing the change, so
// that the VSELECT optimizations that expect the correct vector boolean
// value will not be triggered.
for (SDNode *U : Cond->uses()) {
SDValue SB = DAG.getNode(X86ISD::SHRUNKBLEND, SDLoc(U),
U->getValueType(0), Cond, U->getOperand(1),
U->getOperand(2));
DAG.ReplaceAllUsesOfValueWith(SDValue(U, 0), SB);
}
DCI.CommitTargetLoweringOpt(TLO);
return SDValue();
}
// At this point, only Cond is changed. Change the condition
// just for N to keep the opportunity to optimize all other
// users their own way.
DAG.ReplaceAllUsesOfValueWith(
SDValue(N, 0),
DAG.getNode(X86ISD::SHRUNKBLEND, SDLoc(N), N->getValueType(0),
TLO.New, N->getOperand(1), N->getOperand(2)));
// Only Cond (rather than other nodes in the computation chain) was
// changed. Change the condition just for N to keep the opportunity to
// optimize all other users their own way.
SDValue SB = DAG.getNode(X86ISD::SHRUNKBLEND, DL, VT, TLO.New, LHS, RHS);
DAG.ReplaceAllUsesOfValueWith(SDValue(N, 0), SB);
return SDValue();
}
}

6
lib/Target/X86/X86ISelLowering.h
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@ -195,9 +195,9 @@ namespace llvm {
/// Blend where the selector is an immediate.
BLENDI,
/// Blend where the condition has been shrunk.
/// This is used to emphasize that the condition mask is
/// no more valid for generic VSELECT optimizations.
/// Dynamic (non-constant condition) vector blend where only the sign bits
/// of the condition elements are used. This is used to enforce that the
/// condition mask is not valid for generic VSELECT optimizations.
SHRUNKBLEND,
/// Combined add and sub on an FP vector.