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Add support for computing "zext of value" in KnownBits. NFCI 

Summary:
The description of KnownBits::zext() and
KnownBits::zextOrTrunc() has confusingly been telling
that the operation is equivalent to zero extending the
value we're tracking. That has not been true, instead
the user has been forced to explicitly set the extended
bits as known zero afterwards.

This patch adds a second argument to KnownBits::zext()
and KnownBits::zextOrTrunc() to control if the extended
bits should be considered as known zero or as unknown.

Reviewers: craig.topper, RKSimon

Reviewed By: RKSimon

Subscribers: javed.absar, hiraditya, jdoerfert, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D58650

llvm-svn: 355099
This commit is contained in:
Bjorn Pettersson 2019-02-28 15:45:29 +00:00
parent 3a24cb00eb
commit d30f308a9f
9 changed files with 35 additions and 35 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

24
llvm/include/llvm/Support/KnownBits.h
View File

@ -113,10 +113,16 @@ public:
return KnownBits(Zero.trunc(BitWidth), One.trunc(BitWidth));
}
/// Zero extends the underlying known Zero and One bits. This is equivalent
/// to zero extending the value we're tracking.
KnownBits zext(unsigned BitWidth) {
return KnownBits(Zero.zext(BitWidth), One.zext(BitWidth));
/// Extends the underlying known Zero and One bits.
/// By setting ExtendedBitsAreKnownZero=true this will be equivalent to
/// zero extending the value we're tracking.
/// With ExtendedBitsAreKnownZero=false the extended bits are set to unknown.
KnownBits zext(unsigned BitWidth, bool ExtendedBitsAreKnownZero) {
unsigned OldBitWidth = getBitWidth();
APInt NewZero = Zero.zext(BitWidth);
if (ExtendedBitsAreKnownZero)
NewZero.setBitsFrom(OldBitWidth);
return KnownBits(NewZero, One.zext(BitWidth));
}
/// Sign extends the underlying known Zero and One bits. This is equivalent
@ -125,9 +131,13 @@ public:
return KnownBits(Zero.sext(BitWidth), One.sext(BitWidth));
}
/// Zero extends or truncates the underlying known Zero and One bits. This is
/// equivalent to zero extending or truncating the value we're tracking.
KnownBits zextOrTrunc(unsigned BitWidth) {
/// Extends or truncates the underlying known Zero and One bits. When
/// extending the extended bits can either be set as known zero (if
/// ExtendedBitsAreKnownZero=true) or as unknown (if
/// ExtendedBitsAreKnownZero=false).
KnownBits zextOrTrunc(unsigned BitWidth, bool ExtendedBitsAreKnownZero) {
if (BitWidth > getBitWidth())
return zext(BitWidth, ExtendedBitsAreKnownZero);
return KnownBits(Zero.zextOrTrunc(BitWidth), One.zextOrTrunc(BitWidth));
}

7
llvm/lib/Analysis/ValueTracking.cpp
View File

@ -1128,12 +1128,9 @@ static void computeKnownBitsFromOperator(const Operator *I, KnownBits &Known,
Q.DL.getTypeSizeInBits(ScalarTy);
assert(SrcBitWidth && "SrcBitWidth can't be zero");
Known = Known.zextOrTrunc(SrcBitWidth);
Known = Known.zextOrTrunc(SrcBitWidth, false);
computeKnownBits(I->getOperand(0), Known, Depth + 1, Q);
Known = Known.zextOrTrunc(BitWidth);
// Any top bits are known to be zero.
if (BitWidth > SrcBitWidth)
Known.Zero.setBitsFrom(SrcBitWidth);
Known = Known.zextOrTrunc(BitWidth, true /* ExtendedBitsAreKnownZero */);
break;
}
case Instruction::BitCast: {

2
llvm/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp
View File

@ -400,7 +400,7 @@ FunctionLoweringInfo::GetLiveOutRegInfo(unsigned Reg, unsigned BitWidth) {
if (BitWidth > LOI->Known.getBitWidth()) {
LOI->NumSignBits = 1;
LOI->Known = LOI->Known.zextOrTrunc(BitWidth);
LOI->Known = LOI->Known.zext(BitWidth, false /* => any extend */);
}
return LOI;

11
llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
View File

@ -2800,15 +2800,12 @@ KnownBits SelectionDAG::computeKnownBits(SDValue Op, const APInt &DemandedElts,
EVT InVT = Op.getOperand(0).getValueType();
APInt InDemandedElts = DemandedElts.zextOrSelf(InVT.getVectorNumElements());
Known = computeKnownBits(Op.getOperand(0), InDemandedElts, Depth + 1);
Known = Known.zext(BitWidth);
Known.Zero.setBitsFrom(InVT.getScalarSizeInBits());
Known = Known.zext(BitWidth, true /* ExtendedBitsAreKnownZero */);
break;
}
case ISD::ZERO_EXTEND: {
EVT InVT = Op.getOperand(0).getValueType();
Known = computeKnownBits(Op.getOperand(0), DemandedElts, Depth + 1);
Known = Known.zext(BitWidth);
Known.Zero.setBitsFrom(InVT.getScalarSizeInBits());
Known = Known.zext(BitWidth, true /* ExtendedBitsAreKnownZero */);
break;
}
case ISD::SIGN_EXTEND_VECTOR_INREG: {
@ -2829,7 +2826,7 @@ KnownBits SelectionDAG::computeKnownBits(SDValue Op, const APInt &DemandedElts,
}
case ISD::ANY_EXTEND: {
Known = computeKnownBits(Op.getOperand(0), Depth+1);
Known = Known.zext(BitWidth);
Known = Known.zext(BitWidth, false /* ExtendedBitsAreKnownZero */);
break;
}
case ISD::TRUNCATE: {
@ -3026,7 +3023,7 @@ KnownBits SelectionDAG::computeKnownBits(SDValue Op, const APInt &DemandedElts,
Known = computeKnownBits(InVec, Depth + 1);
}
if (BitWidth > EltBitWidth)
Known = Known.zext(BitWidth);
Known = Known.zext(BitWidth, false /* => any extend */);
break;
}
case ISD::INSERT_VECTOR_ELT: {

8
llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
View File

@ -1163,8 +1163,8 @@ bool TargetLowering::SimplifyDemandedBits(
if (SimplifyDemandedBits(Src, InDemandedBits, Known, TLO, Depth + 1))
return true;
assert(!Known.hasConflict() && "Bits known to be one AND zero?");
Known = Known.zext(BitWidth);
Known.Zero.setBitsFrom(InBits);
assert(Known.getBitWidth() == InBits && "Src width has changed?");
Known = Known.zext(BitWidth, true /* ExtendedBitsAreKnownZero */);
break;
}
case ISD::SIGN_EXTEND: {
@ -1217,7 +1217,7 @@ bool TargetLowering::SimplifyDemandedBits(
if (SimplifyDemandedBits(Src, InDemandedBits, Known, TLO, Depth + 1))
return true;
assert(!Known.hasConflict() && "Bits known to be one AND zero?");
Known = Known.zext(BitWidth);
Known = Known.zext(BitWidth, false /* => any extend */);
break;
}
case ISD::TRUNCATE: {
@ -1312,7 +1312,7 @@ bool TargetLowering::SimplifyDemandedBits(
Known = Known2;
if (BitWidth > EltBitWidth)
Known = Known.zext(BitWidth);
Known = Known.zext(BitWidth, false /* => any extend */);
break;
}
case ISD::BITCAST: {

3
llvm/lib/Target/ARM/ARMISelLowering.cpp
View File

@ -13706,8 +13706,7 @@ void ARMTargetLowering::computeKnownBitsForTargetNode(const SDValue Op,
if (Op.getOpcode() == ARMISD::VGETLANEs)
Known = Known.sext(DstSz);
else {
Known = Known.zext(DstSz);
Known.Zero.setBitsFrom(SrcSz);
Known = Known.zext(DstSz, true /* extended bits are known zero */);
}
assert(DstSz == Known.getBitWidth());
break;

6
llvm/lib/Target/SystemZ/SystemZISelLowering.cpp
View File

@ -6053,12 +6053,10 @@ SystemZTargetLowering::computeKnownBitsForTargetNode(const SDValue Op,
case Intrinsic::s390_vuplhw:
case Intrinsic::s390_vuplf: {
SDValue SrcOp = Op.getOperand(1);
unsigned SrcBitWidth = SrcOp.getScalarValueSizeInBits();
APInt SrcDemE = getDemandedSrcElements(Op, DemandedElts, 0);
Known = DAG.computeKnownBits(SrcOp, SrcDemE, Depth + 1);
if (IsLogical) {
Known = Known.zext(BitWidth);
Known.Zero.setBitsFrom(SrcBitWidth);
Known = Known.zext(BitWidth, true);
} else
Known = Known.sext(BitWidth);
break;
@ -6087,7 +6085,7 @@ SystemZTargetLowering::computeKnownBitsForTargetNode(const SDValue Op,
// Known has the width of the source operand(s). Adjust if needed to match
// the passed bitwidth.
if (Known.getBitWidth() != BitWidth)
Known = Known.zextOrTrunc(BitWidth);
Known = Known.zextOrTrunc(BitWidth, false);
}
static unsigned computeNumSignBitsBinOp(SDValue Op, const APInt &DemandedElts,

2
llvm/lib/Target/X86/X86ISelLowering.cpp
View File

@ -30412,7 +30412,7 @@ void X86TargetLowering::computeKnownBitsForTargetNode(const SDValue Op,
APInt DemandedElt = APInt::getOneBitSet(SrcVT.getVectorNumElements(),
Op.getConstantOperandVal(1));
Known = DAG.computeKnownBits(Src, DemandedElt, Depth + 1);
Known = Known.zextOrTrunc(BitWidth);
Known = Known.zextOrTrunc(BitWidth, false);
Known.Zero.setBitsFrom(SrcVT.getScalarSizeInBits());
break;
}

7
llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
View File

@ -365,10 +365,9 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
KnownBits InputKnown(SrcBitWidth);
if (SimplifyDemandedBits(I, 0, InputDemandedMask, InputKnown, Depth + 1))
return I;
Known = InputKnown.zextOrTrunc(BitWidth);
// Any top bits are known to be zero.
if (BitWidth > SrcBitWidth)
Known.Zero.setBitsFrom(SrcBitWidth);
assert(InputKnown.getBitWidth() == SrcBitWidth && "Src width changed?");
Known = InputKnown.zextOrTrunc(BitWidth,
true /* ExtendedBitsAreKnownZero */);
assert(!Known.hasConflict() && "Bits known to be one AND zero?");
break;
}