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[SDAG] Preserve InBounds in DAGCombines #165424

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[SDAG] Preserve InBounds in DAGCombines #165424

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21 changes: 19 additions & 2 deletions llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2715,6 +2715,12 @@ SDValue DAGCombiner::visitPTRADD(SDNode *N) {
(N->getFlags() & N0->getFlags()) & SDNodeFlags::NoUnsignedWrap;
SDValue Add = DAG.getNode(ISD::ADD, DL, IntVT, {Y, Z}, Flags);
AddToWorklist(Add.getNode());
// We can't set InBounds even if both original ptradds were InBounds and
// NUW: SDAG usually represents pointers as integers, therefore, the
// matched pattern behaves as if it had implicit casts:
// (ptradd inbounds (inttoptr (ptrtoint (ptradd inbounds x, y))), z)
// The outer inbounds ptradd might therefore rely on a provenance that x
// does not have.
return DAG.getMemBasePlusOffset(X, Add, DL, Flags);
}
}
Expand All @@ -2740,6 +2746,12 @@ SDValue DAGCombiner::visitPTRADD(SDNode *N) {
// that.
SDNodeFlags Flags =
(N->getFlags() & N0->getFlags()) & SDNodeFlags::NoUnsignedWrap;
// We can't set InBounds even if both original ptradds were InBounds and
// NUW: SDAG usually represents pointers as integers, therefore, the
// matched pattern behaves as if it had implicit casts:
// (ptradd inbounds (inttoptr (ptrtoint (ptradd inbounds GA, v))), c)
// The outer inbounds ptradd might therefore rely on a provenance that
// GA does not have.
SDValue Inner = DAG.getMemBasePlusOffset(GAValue, N1, DL, Flags);
AddToWorklist(Inner.getNode());
return DAG.getMemBasePlusOffset(Inner, N0.getOperand(1), DL, Flags);
Expand All @@ -2763,8 +2775,13 @@ SDValue DAGCombiner::visitPTRADD(SDNode *N) {
bool ZIsConstant = DAG.isConstantIntBuildVectorOrConstantInt(Z);

// If both additions in the original were NUW, reassociation preserves that.
SDNodeFlags ReassocFlags =
(N->getFlags() & N1->getFlags()) & SDNodeFlags::NoUnsignedWrap;
SDNodeFlags CommonFlags = N->getFlags() & N1->getFlags();
SDNodeFlags ReassocFlags = CommonFlags & SDNodeFlags::NoUnsignedWrap;
if (CommonFlags.hasNoUnsignedWrap()) {
// If both operations are NUW and the PTRADD is inbounds, the offests are
// both non-negative, so the reassociated PTRADDs are also inbounds.
ReassocFlags |= N->getFlags() & SDNodeFlags::InBounds;
}

if (ZIsConstant != YIsConstant) {
if (YIsConstant)
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