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[SDAG] Introduce inbounds flag for ISD::PTRADD #162477

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[SDAG] Introduce inbounds flag for ISD::PTRADD #162477

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a8f0109
[SDAG] Introduce inbounds flag for ISD::PTRADD
ritter-x2a Oct 8, 2025
dae2e12
Add a warning comment about the limited provenance guarantees with PT…
ritter-x2a Oct 10, 2025
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13 changes: 11 additions & 2 deletions llvm/include/llvm/CodeGen/SelectionDAGNodes.h
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Expand Up @@ -418,12 +418,19 @@ struct SDNodeFlags {
Unpredictable = 1 << 13,
// Compare instructions which may carry the samesign flag.
SameSign = 1 << 14,
// ISD::PTRADD operations that remain in bounds, i.e., the left operand is
// an address in a memory object in which the result of the operation also
// lies. WARNING: Since SDAG does not have pointer types, a PTRADD's pointer
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Nit: As part of the CHERI upstreaming work we do now have a c64/c128 type which is actually a pointer type.

Suggested change
// lies. WARNING: Since SDAG does not have pointer types, a PTRADD's pointer
// lies. WARNING: Since SDAG generally uses integers instead of pointer types, a PTRADD's pointer

// operand is effectively the result of an implicit inttoptr cast. This
// limits any provenance information implied by the InBounds flag and the
// possible transformations based on it.
InBounds = 1 << 15,

// NOTE: Please update LargestValue in LLVM_DECLARE_ENUM_AS_BITMASK below
// the class definition when adding new flags.

PoisonGeneratingFlags = NoUnsignedWrap | NoSignedWrap | Exact | Disjoint |
NonNeg | NoNaNs | NoInfs | SameSign,
NonNeg | NoNaNs | NoInfs | SameSign | InBounds,
FastMathFlags = NoNaNs | NoInfs | NoSignedZeros | AllowReciprocal |
AllowContract | ApproximateFuncs | AllowReassociation,
};
Expand Down Expand Up @@ -458,6 +465,7 @@ struct SDNodeFlags {
void setAllowReassociation(bool b) { setFlag<AllowReassociation>(b); }
void setNoFPExcept(bool b) { setFlag<NoFPExcept>(b); }
void setUnpredictable(bool b) { setFlag<Unpredictable>(b); }
void setInBounds(bool b) { setFlag<InBounds>(b); }

// These are accessors for each flag.
bool hasNoUnsignedWrap() const { return Flags & NoUnsignedWrap; }
Expand All @@ -475,6 +483,7 @@ struct SDNodeFlags {
bool hasAllowReassociation() const { return Flags & AllowReassociation; }
bool hasNoFPExcept() const { return Flags & NoFPExcept; }
bool hasUnpredictable() const { return Flags & Unpredictable; }
bool hasInBounds() const { return Flags & InBounds; }

bool operator==(const SDNodeFlags &Other) const {
return Flags == Other.Flags;
Expand All @@ -484,7 +493,7 @@ struct SDNodeFlags {
};

LLVM_DECLARE_ENUM_AS_BITMASK(decltype(SDNodeFlags::None),
SDNodeFlags::SameSign);
SDNodeFlags::InBounds);

inline SDNodeFlags operator|(SDNodeFlags LHS, SDNodeFlags RHS) {
LHS |= RHS;
Expand Down
5 changes: 4 additions & 1 deletion llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
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Expand Up @@ -8615,7 +8615,10 @@ SDValue SelectionDAG::getMemBasePlusOffset(SDValue Ptr, SDValue Offset,
if (TLI->shouldPreservePtrArith(this->getMachineFunction().getFunction(),
BasePtrVT))
return getNode(ISD::PTRADD, DL, BasePtrVT, Ptr, Offset, Flags);
return getNode(ISD::ADD, DL, BasePtrVT, Ptr, Offset, Flags);
// InBounds only applies to PTRADD, don't set it if we generate ADD.
SDNodeFlags AddFlags = Flags;
AddFlags.setInBounds(false);
return getNode(ISD::ADD, DL, BasePtrVT, Ptr, Offset, AddFlags);
}

/// Returns true if memcpy source is constant data.
Expand Down
3 changes: 3 additions & 0 deletions llvm/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
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Expand Up @@ -4375,6 +4375,7 @@ void SelectionDAGBuilder::visitGetElementPtr(const User &I) {
if (NW.hasNoUnsignedWrap() ||
(int64_t(Offset) >= 0 && NW.hasNoUnsignedSignedWrap()))
Flags |= SDNodeFlags::NoUnsignedWrap;
Flags.setInBounds(NW.isInBounds());

N = DAG.getMemBasePlusOffset(
N, DAG.getConstant(Offset, dl, N.getValueType()), dl, Flags);
Expand Down Expand Up @@ -4418,6 +4419,7 @@ void SelectionDAGBuilder::visitGetElementPtr(const User &I) {
if (NW.hasNoUnsignedWrap() ||
(Offs.isNonNegative() && NW.hasNoUnsignedSignedWrap()))
Flags.setNoUnsignedWrap(true);
Flags.setInBounds(NW.isInBounds());

OffsVal = DAG.getSExtOrTrunc(OffsVal, dl, N.getValueType());

Expand Down Expand Up @@ -4487,6 +4489,7 @@ void SelectionDAGBuilder::visitGetElementPtr(const User &I) {
// pointer index type (add nuw).
SDNodeFlags AddFlags;
AddFlags.setNoUnsignedWrap(NW.hasNoUnsignedWrap());
AddFlags.setInBounds(NW.isInBounds());

N = DAG.getMemBasePlusOffset(N, IdxN, dl, AddFlags);
}
Expand Down
3 changes: 3 additions & 0 deletions llvm/lib/CodeGen/SelectionDAG/SelectionDAGDumper.cpp
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Expand Up @@ -688,6 +688,9 @@ void SDNode::print_details(raw_ostream &OS, const SelectionDAG *G) const {
if (getFlags().hasSameSign())
OS << " samesign";

if (getFlags().hasInBounds())
OS << " inbounds";

if (getFlags().hasNonNeg())
OS << " nneg";

Expand Down