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[InstCombine] Fold icmp of gep chain with base #144065

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[InstCombine] Fold icmp of gep chain with base #144065

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b1e4bf8
Add icmp gep chain tests
nikic Jun 13, 2025
f223184
[InstCombine] Fold icmp of gep chain with base
nikic Jun 11, 2025
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9 changes: 6 additions & 3 deletions llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -708,10 +708,12 @@ Instruction *InstCombinerImpl::foldGEPICmp(GEPOperator *GEPLHS, Value *RHS,
return I;
};

Value *PtrBase = GEPLHS->getOperand(0);
if (PtrBase == RHS && CanFold(GEPLHS->getNoWrapFlags())) {
CommonPointerBase Base = CommonPointerBase::compute(GEPLHS, RHS);
if (Base.Ptr == RHS && CanFold(Base.LHSNW)) {
// ((gep Ptr, OFFSET) cmp Ptr) ---> (OFFSET cmp 0).
Value *Offset = EmitGEPOffset(GEPLHS);
Type *IdxTy = DL.getIndexType(GEPLHS->getType());
Value *Offset =
EmitGEPOffsets(Base.LHSGEPs, Base.LHSNW, IdxTy, /*RewriteGEPs=*/false);
return NewICmp(GEPLHS->getNoWrapFlags(), Offset,
Constant::getNullValue(Offset->getType()));
}
Expand Down Expand Up @@ -750,6 +752,7 @@ Instruction *InstCombinerImpl::foldGEPICmp(GEPOperator *GEPLHS, Value *RHS,

// If the base pointers are different, but the indices are the same, just
// compare the base pointer.
Value *PtrBase = GEPLHS->getOperand(0);
if (PtrBase != GEPRHS->getOperand(0)) {
bool IndicesTheSame =
GEPLHS->getNumOperands() == GEPRHS->getNumOperands() &&
Expand Down
2 changes: 1 addition & 1 deletion llvm/test/Transforms/InstCombine/getelementptr.ll
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Expand Up @@ -694,7 +694,7 @@ define i32 @test28() nounwind {
; CHECK-NEXT: [[TMP0:%.*]] = sext i32 [[T12_REC]] to i64
; CHECK-NEXT: [[T12:%.*]] = getelementptr inbounds [[STRUCT_X:%.*]], ptr [[T45]], i64 [[TMP0]]
; CHECK-NEXT: [[T16:%.*]] = call i32 (ptr, ...) @printf(ptr noundef nonnull dereferenceable(1) @.str1, ptr nonnull [[T12]]) #[[ATTR0]]
; CHECK-NEXT: [[T84:%.*]] = icmp eq ptr [[T12]], [[ORIENTATIONS]]
; CHECK-NEXT: [[T84:%.*]] = icmp eq i32 [[INDVAR]], 0
; CHECK-NEXT: [[INDVAR_NEXT]] = add i32 [[INDVAR]], 1
; CHECK-NEXT: br i1 [[T84]], label [[BB17:%.*]], label [[BB10]]
; CHECK: bb17:
Expand Down
64 changes: 64 additions & 0 deletions llvm/test/Transforms/InstCombine/icmp-gep.ll
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Expand Up @@ -757,3 +757,67 @@ define i1 @gep_diff_base_same_indices_nuw_nusw(ptr %x, ptr %y, i64 %z) {
%cmp = icmp ult ptr %gep1, %gep2
ret i1 %cmp
}

define i1 @gep_multiple_eq(ptr %base, i64 %idx, i64 %idx2) {
; CHECK-LABEL: @gep_multiple_eq(
; CHECK-NEXT: [[GEP1_IDX1:%.*]] = add i64 [[IDX:%.*]], [[IDX2:%.*]]
; CHECK-NEXT: [[DOTMASK:%.*]] = and i64 [[GEP1_IDX1]], 4611686018427387903
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i64 [[DOTMASK]], 0
; CHECK-NEXT: ret i1 [[CMP]]
;
%gep1 = getelementptr i32, ptr %base, i64 %idx
%gep2 = getelementptr i32, ptr %gep1, i64 %idx2
%cmp = icmp eq ptr %gep2, %base
ret i1 %cmp
}

define i1 @gep_multiple_eq_commuted(ptr %base, i64 %idx, i64 %idx2) {
; CHECK-LABEL: @gep_multiple_eq_commuted(
; CHECK-NEXT: [[GEP1_IDX1:%.*]] = add i64 [[IDX:%.*]], [[IDX2:%.*]]
; CHECK-NEXT: [[DOTMASK:%.*]] = and i64 [[GEP1_IDX1]], 4611686018427387903
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i64 [[DOTMASK]], 0
; CHECK-NEXT: ret i1 [[CMP]]
;
%gep1 = getelementptr i32, ptr %base, i64 %idx
%gep2 = getelementptr i32, ptr %gep1, i64 %idx2
%cmp = icmp eq ptr %base, %gep2
ret i1 %cmp
}

define i1 @gep_mugtiple_ugt_nuw(ptr %base, i64 %idx, i64 %idx2) {
; CHECK-LABEL: @gep_mugtiple_ugt_nuw(
; CHECK-NEXT: [[GEP1_IDX1:%.*]] = sub i64 0, [[IDX2:%.*]]
; CHECK-NEXT: [[CMP:%.*]] = icmp ne i64 [[IDX:%.*]], [[GEP1_IDX1]]
; CHECK-NEXT: ret i1 [[CMP]]
;
%gep1 = getelementptr nuw i32, ptr %base, i64 %idx
%gep2 = getelementptr nuw i32, ptr %gep1, i64 %idx2
%cmp = icmp ugt ptr %gep2, %base
ret i1 %cmp
}

define i1 @gep_mugtiple_ugt_not_all_nuw(ptr %base, i64 %idx, i64 %idx2) {
; CHECK-LABEL: @gep_mugtiple_ugt_not_all_nuw(
; CHECK-NEXT: [[GEP1:%.*]] = getelementptr nuw i32, ptr [[BASE:%.*]], i64 [[IDX:%.*]]
; CHECK-NEXT: [[GEP2:%.*]] = getelementptr i32, ptr [[GEP1]], i64 [[IDX2:%.*]]
; CHECK-NEXT: [[CMP:%.*]] = icmp ugt ptr [[GEP2]], [[BASE]]
; CHECK-NEXT: ret i1 [[CMP]]
;
%gep1 = getelementptr nuw i32, ptr %base, i64 %idx
%gep2 = getelementptr i32, ptr %gep1, i64 %idx2
%cmp = icmp ugt ptr %gep2, %base
ret i1 %cmp
}

define i1 @gep_mugtiple_ugt_inbounds_nusw(ptr %base, i64 %idx, i64 %idx2) {
; CHECK-LABEL: @gep_mugtiple_ugt_inbounds_nusw(
; CHECK-NEXT: [[GEP1_IDX1:%.*]] = add i64 [[IDX:%.*]], [[IDX2:%.*]]
; CHECK-NEXT: [[TMP1:%.*]] = shl i64 [[GEP1_IDX1]], 2
; CHECK-NEXT: [[CMP:%.*]] = icmp sgt i64 [[TMP1]], 0
; CHECK-NEXT: ret i1 [[CMP]]
;
%gep1 = getelementptr inbounds i32, ptr %base, i64 %idx
%gep2 = getelementptr nusw i32, ptr %gep1, i64 %idx2
%cmp = icmp ugt ptr %gep2, %base
ret i1 %cmp
}
12 changes: 3 additions & 9 deletions llvm/test/Transforms/InstCombine/pr39908.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -7,9 +7,7 @@ target datalayout = "p:32:32"

define i1 @test(ptr %p, i32 %n) {
; CHECK-LABEL: @test(
; CHECK-NEXT: [[END:%.*]] = getelementptr inbounds [0 x %S], ptr [[P:%.*]], i32 0, i32 [[N:%.*]], i32 0, i32 0
; CHECK-NEXT: [[LAST:%.*]] = getelementptr inbounds i8, ptr [[END]], i32 -8
; CHECK-NEXT: [[CMP:%.*]] = icmp eq ptr [[LAST]], [[P]]
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[N:%.*]], 1
; CHECK-NEXT: ret i1 [[CMP]]
;
%end = getelementptr inbounds [0 x %S], ptr %p, i32 0, i32 %n, i32 0, i32 0
Expand All @@ -22,9 +20,7 @@ define i1 @test(ptr %p, i32 %n) {
define i1 @test64(ptr %p, i64 %n) {
; CHECK-LABEL: @test64(
; CHECK-NEXT: [[TMP1:%.*]] = trunc i64 [[N:%.*]] to i32
; CHECK-NEXT: [[END:%.*]] = getelementptr inbounds [0 x %S], ptr [[P:%.*]], i32 0, i32 [[TMP1]], i32 0, i32 0
; CHECK-NEXT: [[LAST:%.*]] = getelementptr inbounds i8, ptr [[END]], i32 -8
; CHECK-NEXT: [[CMP:%.*]] = icmp eq ptr [[LAST]], [[P]]
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[TMP1]], 1
; CHECK-NEXT: ret i1 [[CMP]]
;
%end = getelementptr inbounds [0 x %S], ptr %p, i64 0, i64 %n, i32 0, i64 0
Expand All @@ -37,9 +33,7 @@ define i1 @test64(ptr %p, i64 %n) {
define i1 @test64_overflow(ptr %p, i64 %n) {
; CHECK-LABEL: @test64_overflow(
; CHECK-NEXT: [[TMP1:%.*]] = trunc i64 [[N:%.*]] to i32
; CHECK-NEXT: [[END:%.*]] = getelementptr inbounds [0 x %S], ptr [[P:%.*]], i32 0, i32 [[TMP1]], i32 0, i32 0
; CHECK-NEXT: [[LAST:%.*]] = getelementptr inbounds i8, ptr [[END]], i32 -8
; CHECK-NEXT: [[CMP:%.*]] = icmp eq ptr [[LAST]], [[P]]
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i32 [[TMP1]], 1
; CHECK-NEXT: ret i1 [[CMP]]
;
%end = getelementptr inbounds [0 x %S], ptr %p, i64 0, i64 %n, i32 0, i64 8589934592
Expand Down
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