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[InstCombine] Check nowrap flags when folding comparison of GEPs with the same base pointer #121892

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Merged
merged 4 commits into from
Feb 1, 2025
Merged

[InstCombine] Check nowrap flags when folding comparison of GEPs with the same base pointer #121892

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a3fa390
[InstCombine] Add pre-commit tests. NFC.
dtcxzyw Jan 7, 2025
b14982b
[InstCombine] Check nowrap flags when folding comparison of GEPs with…
dtcxzyw Jan 7, 2025
d59529c
[InstCombine] Address review comments. NFC.
dtcxzyw Jan 7, 2025
1cf4654
format
dtcxzyw Feb 1, 2025
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5 changes: 3 additions & 2 deletions llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -834,8 +834,9 @@ Instruction *InstCombinerImpl::foldGEPICmp(GEPOperator *GEPLHS, Value *RHS,
return replaceInstUsesWith(
I, // No comparison is needed here.
ConstantInt::get(I.getType(), ICmpInst::isTrueWhenEqual(Cond)));

else if (NumDifferences == 1 && CanFold(NW)) {
// If two GEPs only differ by an index, compare them.
// Note that nowrap flags are always needed when comparing two indices.
else if (NumDifferences == 1 && NW != GEPNoWrapFlags::none()) {
Value *LHSV = GEPLHS->getOperand(DiffOperand);
Value *RHSV = GEPRHS->getOperand(DiffOperand);
return NewICmp(NW, LHSV, RHSV);
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35 changes: 35 additions & 0 deletions llvm/test/Transforms/InstCombine/opaque-ptr.ll
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Expand Up @@ -467,6 +467,41 @@ define i1 @cmp_gep_same_base_same_type(ptr %ptr, i64 %idx1, i64 %idx2) {
ret i1 %cmp
}

define i1 @cmp_gep_same_base_same_type_maywrap(ptr %ptr, i64 %idx1, i64 %idx2) {
; CHECK-LABEL: @cmp_gep_same_base_same_type_maywrap(
; CHECK-NEXT: [[CMP_UNSHIFTED:%.*]] = xor i64 [[IDX1:%.*]], [[IDX2:%.*]]
; CHECK-NEXT: [[CMP_MASK:%.*]] = and i64 [[CMP_UNSHIFTED]], 4611686018427387903
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i64 [[CMP_MASK]], 0
; CHECK-NEXT: ret i1 [[CMP]]
;
%gep1 = getelementptr i32, ptr %ptr, i64 %idx1
%gep2 = getelementptr i32, ptr %ptr, i64 %idx2
%cmp = icmp eq ptr %gep1, %gep2
ret i1 %cmp
}

define i1 @cmp_gep_same_base_same_type_nuw(ptr %ptr, i64 %idx1, i64 %idx2) {
; CHECK-LABEL: @cmp_gep_same_base_same_type_nuw(
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i64 [[IDX1:%.*]], [[IDX2:%.*]]
; CHECK-NEXT: ret i1 [[CMP]]
;
%gep1 = getelementptr nuw i32, ptr %ptr, i64 %idx1
%gep2 = getelementptr nuw i32, ptr %ptr, i64 %idx2
%cmp = icmp eq ptr %gep1, %gep2
ret i1 %cmp
}

define i1 @cmp_gep_same_base_same_type_nusw(ptr %ptr, i64 %idx1, i64 %idx2) {
; CHECK-LABEL: @cmp_gep_same_base_same_type_nusw(
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i64 [[IDX1:%.*]], [[IDX2:%.*]]
; CHECK-NEXT: ret i1 [[CMP]]
;
%gep1 = getelementptr nusw i32, ptr %ptr, i64 %idx1
%gep2 = getelementptr nusw i32, ptr %ptr, i64 %idx2
%cmp = icmp eq ptr %gep1, %gep2
ret i1 %cmp
}

define i1 @cmp_gep_same_base_different_type(ptr %ptr, i64 %idx1, i64 %idx2) {
; CHECK-LABEL: @cmp_gep_same_base_different_type(
; CHECK-NEXT: [[GEP1_IDX:%.*]] = shl nsw i64 [[IDX1:%.*]], 2
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