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[InstCombine] Preserve flags for difference of gep chains #143488

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Merged
merged 1 commit into from
Jun 10, 2025
Merged

[InstCombine] Preserve flags for difference of gep chains #143488

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10 changes: 6 additions & 4 deletions llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2146,12 +2146,14 @@ Value *InstCombinerImpl::OptimizePointerDifference(Value *LHS, Value *RHS,
bool RewriteGEPs = !Base.LHSGEPs.empty() && !Base.RHSGEPs.empty();

Type *IdxTy = DL.getIndexType(Base.Ptr->getType());
auto EmitOffsetFromBase = [&](ArrayRef<GEPOperator *> GEPs) -> Value * {
auto EmitOffsetFromBase = [&](ArrayRef<GEPOperator *> GEPs,
GEPNoWrapFlags NW) -> Value * {
Value *Sum = nullptr;
for (GEPOperator *GEP : reverse(GEPs)) {
Value *Offset = EmitGEPOffset(GEP, RewriteGEPs);
if (Sum)
Sum = Builder.CreateAdd(Sum, Offset);
Sum = Builder.CreateAdd(Sum, Offset, "", NW.hasNoUnsignedWrap(),
NW.isInBounds());
else
Sum = Offset;
}
Expand All @@ -2160,8 +2162,8 @@ Value *InstCombinerImpl::OptimizePointerDifference(Value *LHS, Value *RHS,
return Sum;
};

Value *Result = EmitOffsetFromBase(Base.LHSGEPs);
Value *Offset2 = EmitOffsetFromBase(Base.RHSGEPs);
Value *Result = EmitOffsetFromBase(Base.LHSGEPs, Base.LHSNW);
Value *Offset2 = EmitOffsetFromBase(Base.RHSGEPs, Base.RHSNW);

// If this is a single inbounds GEP and the original sub was nuw,
// then the final multiplication is also nuw.
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6 changes: 3 additions & 3 deletions llvm/test/Transforms/InstCombine/sub-gep.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -945,7 +945,7 @@ define i64 @multiple_geps_two_chains_gep_base(ptr %base, i64 %base.idx, i64 %idx

define i64 @multiple_geps_inbounds(ptr %base, i64 %idx, i64 %idx2) {
; CHECK-LABEL: @multiple_geps_inbounds(
; CHECK-NEXT: [[D:%.*]] = add i64 [[IDX:%.*]], [[IDX2:%.*]]
; CHECK-NEXT: [[D:%.*]] = add nsw i64 [[IDX:%.*]], [[IDX2:%.*]]
; CHECK-NEXT: ret i64 [[D]]
;
%p2 = getelementptr inbounds i8, ptr %base, i64 %idx
Expand All @@ -971,7 +971,7 @@ define i64 @multiple_geps_nusw(ptr %base, i64 %idx, i64 %idx2) {

define i64 @multiple_geps_nuw(ptr %base, i64 %idx, i64 %idx2) {
; CHECK-LABEL: @multiple_geps_nuw(
; CHECK-NEXT: [[D:%.*]] = add i64 [[IDX:%.*]], [[IDX2:%.*]]
; CHECK-NEXT: [[D:%.*]] = add nuw i64 [[IDX:%.*]], [[IDX2:%.*]]
; CHECK-NEXT: ret i64 [[D]]
;
%p2 = getelementptr nuw i8, ptr %base, i64 %idx
Expand All @@ -985,7 +985,7 @@ define i64 @multiple_geps_nuw(ptr %base, i64 %idx, i64 %idx2) {

define i64 @multiple_geps_inbounds_nuw(ptr %base, i64 %idx, i64 %idx2) {
; CHECK-LABEL: @multiple_geps_inbounds_nuw(
; CHECK-NEXT: [[D:%.*]] = add i64 [[IDX:%.*]], [[IDX2:%.*]]
; CHECK-NEXT: [[D:%.*]] = add nuw nsw i64 [[IDX:%.*]], [[IDX2:%.*]]
; CHECK-NEXT: ret i64 [[D]]
;
%p2 = getelementptr inbounds nuw i8, ptr %base, i64 %idx
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