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[InstCombine] Fix multi-use handling for multi-GEP rewrite #146689

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Merged
merged 2 commits into from
Jul 2, 2025
Merged

[InstCombine] Fix multi-use handling for multi-GEP rewrite #146689

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5648408
Add extra multi-use test
nikic Jul 2, 2025
dbf821b
fix multi-use handling when expanding multiple gep offsets
nikic Jul 2, 2025
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5 changes: 2 additions & 3 deletions llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -205,9 +205,8 @@ Value *InstCombinerImpl::EmitGEPOffset(GEPOperator *GEP, bool RewriteGEP) {
Builder.SetInsertPoint(Inst);

Value *Offset = EmitGEPOffset(GEP);
// If a non-trivial GEP has other uses, rewrite it to avoid duplicating
// the offset arithmetic.
if (Inst && !GEP->hasOneUse() && !GEP->hasAllConstantIndices() &&
// Rewrite non-trivial GEPs to avoid duplicating the offset arithmetic.
if (Inst && !GEP->hasAllConstantIndices() &&
!GEP->getSourceElementType()->isIntegerTy(8)) {
replaceInstUsesWith(
*Inst, Builder.CreateGEP(Builder.getInt8Ty(), GEP->getPointerOperand(),
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64 changes: 64 additions & 0 deletions llvm/test/Transforms/InstCombine/sub-gep.ll
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Expand Up @@ -943,6 +943,70 @@ define i64 @multiple_geps_two_chains_gep_base(ptr %base, i64 %base.idx, i64 %idx
ret i64 %d
}

define i64 @multiple_geps_two_chains_multi_use(ptr %base, i64 %idx1, i64 %idx2, i64 %idx3, i64 %idx4) {
; CHECK-LABEL: @multiple_geps_two_chains_multi_use(
; CHECK-NEXT: [[P2_IDX:%.*]] = shl nsw i64 [[IDX2:%.*]], 2
; CHECK-NEXT: [[P2:%.*]] = getelementptr inbounds i8, ptr [[P1:%.*]], i64 [[P2_IDX]]
; CHECK-NEXT: [[P4_IDX:%.*]] = shl nsw i64 [[IDX4:%.*]], 2
; CHECK-NEXT: [[P5:%.*]] = getelementptr inbounds i8, ptr [[P2]], i64 [[P4_IDX]]
; CHECK-NEXT: [[P3_IDX:%.*]] = shl nsw i64 [[IDX3:%.*]], 2
; CHECK-NEXT: [[P3:%.*]] = getelementptr inbounds i8, ptr [[P1]], i64 [[P3_IDX]]
; CHECK-NEXT: [[P4_IDX1:%.*]] = shl nsw i64 [[IDX5:%.*]], 2
; CHECK-NEXT: [[P4:%.*]] = getelementptr inbounds i8, ptr [[P3]], i64 [[P4_IDX1]]
; CHECK-NEXT: call void @use(ptr [[P5]])
; CHECK-NEXT: call void @use(ptr [[P4]])
; CHECK-NEXT: [[TMP1:%.*]] = add nsw i64 [[P2_IDX]], [[P4_IDX]]
; CHECK-NEXT: [[TMP2:%.*]] = add nsw i64 [[P3_IDX]], [[P4_IDX1]]
; CHECK-NEXT: [[GEPDIFF:%.*]] = sub nsw i64 [[TMP1]], [[TMP2]]
; CHECK-NEXT: ret i64 [[GEPDIFF]]
;
%p1 = getelementptr inbounds i32, ptr %base, i64 %idx1
%p2 = getelementptr inbounds i32, ptr %p1, i64 %idx2
%p3 = getelementptr inbounds i32, ptr %base, i64 %idx3
%p4 = getelementptr inbounds i32, ptr %p3, i64 %idx4
call void @use(ptr %p2)
call void @use(ptr %p4)
%i1 = ptrtoint ptr %p4 to i64
%i2 = ptrtoint ptr %p2 to i64
%d = sub i64 %i2, %i1
ret i64 %d
}

define i64 @multiple_geps_two_chains_partial_multi_use(ptr %base, i64 %idx1, i64 %idx2, i64 %idx3, i64 %idx4, i64 %idx5, i64 %idx6) {
; CHECK-LABEL: @multiple_geps_two_chains_partial_multi_use(
; CHECK-NEXT: [[P2_IDX:%.*]] = shl nsw i64 [[IDX2:%.*]], 2
; CHECK-NEXT: [[P2:%.*]] = getelementptr inbounds i8, ptr [[P1:%.*]], i64 [[P2_IDX]]
; CHECK-NEXT: [[P4_IDX:%.*]] = shl nsw i64 [[IDX4:%.*]], 2
; CHECK-NEXT: [[P3:%.*]] = getelementptr inbounds i8, ptr [[P2]], i64 [[P4_IDX]]
; CHECK-NEXT: [[P3_IDX:%.*]] = shl nsw i64 [[IDX3:%.*]], 2
; CHECK-NEXT: [[P4_IDX1:%.*]] = shl nsw i64 [[IDX7:%.*]], 2
; CHECK-NEXT: [[P5:%.*]] = getelementptr inbounds i8, ptr [[P1]], i64 [[P4_IDX1]]
; CHECK-NEXT: [[P5_IDX:%.*]] = shl nsw i64 [[IDX5:%.*]], 2
; CHECK-NEXT: [[P4:%.*]] = getelementptr inbounds i8, ptr [[P5]], i64 [[P5_IDX]]
; CHECK-NEXT: [[P6_IDX:%.*]] = shl nsw i64 [[IDX6:%.*]], 2
; CHECK-NEXT: call void @use(ptr [[P3]])
; CHECK-NEXT: call void @use(ptr [[P4]])
; CHECK-NEXT: [[TMP1:%.*]] = add nsw i64 [[P2_IDX]], [[P4_IDX]]
; CHECK-NEXT: [[TMP2:%.*]] = add nsw i64 [[TMP1]], [[P3_IDX]]
; CHECK-NEXT: [[TMP3:%.*]] = add nsw i64 [[P4_IDX1]], [[P5_IDX]]
; CHECK-NEXT: [[TMP4:%.*]] = add nsw i64 [[TMP3]], [[P6_IDX]]
; CHECK-NEXT: [[GEPDIFF:%.*]] = sub nsw i64 [[TMP2]], [[TMP4]]
; CHECK-NEXT: ret i64 [[GEPDIFF]]
;
%p1 = getelementptr inbounds i32, ptr %base, i64 %idx1
%p2 = getelementptr inbounds i32, ptr %p1, i64 %idx2
%p3 = getelementptr inbounds i32, ptr %p2, i64 %idx3
%p4 = getelementptr inbounds i32, ptr %base, i64 %idx4
%p5 = getelementptr inbounds i32, ptr %p4, i64 %idx5
%p6 = getelementptr inbounds i32, ptr %p5, i64 %idx6
call void @use(ptr %p2)
call void @use(ptr %p5)
%i1 = ptrtoint ptr %p6 to i64
%i2 = ptrtoint ptr %p3 to i64
%d = sub i64 %i2, %i1
ret i64 %d
}

define i64 @multiple_geps_inbounds(ptr %base, i64 %idx, i64 %idx2) {
; CHECK-LABEL: @multiple_geps_inbounds(
; CHECK-NEXT: [[D:%.*]] = add nsw i64 [[IDX:%.*]], [[IDX2:%.*]]
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