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[InstCombine] Preserve inbounds when canonicalizing gep+add #90160

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Merged
merged 1 commit into from
Apr 29, 2024
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[InstCombine] Preserve inbounds when canonicalizing gep+add #90160

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34 changes: 26 additions & 8 deletions llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2948,6 +2948,14 @@ Instruction *InstCombinerImpl::visitGetElementPtrInst(GetElementPtrInst &GEP) {
return nullptr;

if (GEP.getNumIndices() == 1) {
// We can only preserve inbounds if the original gep is inbounds, the add
// is nsw, and the add operands are non-negative.
auto CanPreserveInBounds = [&](bool AddIsNSW, Value *Idx1, Value *Idx2) {
SimplifyQuery Q = SQ.getWithInstruction(&GEP);
return GEP.isInBounds() && AddIsNSW && isKnownNonNegative(Idx1, Q) &&
isKnownNonNegative(Idx2, Q);
};

// Try to replace ADD + GEP with GEP + GEP.
Value *Idx1, *Idx2;
if (match(GEP.getOperand(1),
Expand All @@ -2957,10 +2965,15 @@ Instruction *InstCombinerImpl::visitGetElementPtrInst(GetElementPtrInst &GEP) {
// as:
// %newptr = getelementptr i32, ptr %ptr, i64 %idx1
// %newgep = getelementptr i32, ptr %newptr, i64 %idx2
auto *NewPtr = Builder.CreateGEP(GEP.getResultElementType(),
GEP.getPointerOperand(), Idx1);
return GetElementPtrInst::Create(GEP.getResultElementType(), NewPtr,
Idx2);
bool IsInBounds = CanPreserveInBounds(
cast<OverflowingBinaryOperator>(GEP.getOperand(1))->hasNoSignedWrap(),
Idx1, Idx2);
auto *NewPtr =
Builder.CreateGEP(GEP.getResultElementType(), GEP.getPointerOperand(),
Idx1, "", IsInBounds);
return replaceInstUsesWith(
GEP, Builder.CreateGEP(GEP.getResultElementType(), NewPtr, Idx2, "",
IsInBounds));
}
ConstantInt *C;
if (match(GEP.getOperand(1), m_OneUse(m_SExtLike(m_OneUse(m_NSWAdd(
Expand All @@ -2971,12 +2984,17 @@ Instruction *InstCombinerImpl::visitGetElementPtrInst(GetElementPtrInst &GEP) {
// as:
// %newptr = getelementptr i32, ptr %ptr, i32 %idx1
// %newgep = getelementptr i32, ptr %newptr, i32 idx2
bool IsInBounds = CanPreserveInBounds(
/*IsNSW=*/true, Idx1, C);
auto *NewPtr = Builder.CreateGEP(
GEP.getResultElementType(), GEP.getPointerOperand(),
Builder.CreateSExt(Idx1, GEP.getOperand(1)->getType()));
return GetElementPtrInst::Create(
GEP.getResultElementType(), NewPtr,
Builder.CreateSExt(C, GEP.getOperand(1)->getType()));
Builder.CreateSExt(Idx1, GEP.getOperand(1)->getType()), "",
IsInBounds);
return replaceInstUsesWith(
GEP,
Builder.CreateGEP(GEP.getResultElementType(), NewPtr,
Builder.CreateSExt(C, GEP.getOperand(1)->getType()),
"", IsInBounds));
}
}

Expand Down
8 changes: 4 additions & 4 deletions llvm/test/Transforms/InstCombine/array.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -116,8 +116,8 @@ define ptr @gep_inbounds_add_nsw_nonneg(ptr %ptr, i64 %a, i64 %b) {
; CHECK-NEXT: call void @llvm.assume(i1 [[A_NNEG]])
; CHECK-NEXT: [[B_NNEG:%.*]] = icmp sgt i64 [[B]], -1
; CHECK-NEXT: call void @llvm.assume(i1 [[B_NNEG]])
; CHECK-NEXT: [[TMP1:%.*]] = getelementptr i32, ptr [[PTR]], i64 [[A]]
; CHECK-NEXT: [[GEP:%.*]] = getelementptr i32, ptr [[TMP1]], i64 [[B]]
; CHECK-NEXT: [[TMP1:%.*]] = getelementptr inbounds i32, ptr [[PTR]], i64 [[A]]
; CHECK-NEXT: [[GEP:%.*]] = getelementptr inbounds i32, ptr [[TMP1]], i64 [[B]]
; CHECK-NEXT: ret ptr [[GEP]]
;
%a.nneg = icmp sgt i64 %a, -1
Expand Down Expand Up @@ -207,8 +207,8 @@ define ptr @gep_inbounds_sext_add_nonneg(ptr %ptr, i32 %a) {
; CHECK-NEXT: [[A_NNEG:%.*]] = icmp sgt i32 [[A]], -1
; CHECK-NEXT: call void @llvm.assume(i1 [[A_NNEG]])
; CHECK-NEXT: [[TMP1:%.*]] = zext nneg i32 [[A]] to i64
; CHECK-NEXT: [[TMP2:%.*]] = getelementptr i32, ptr [[PTR]], i64 [[TMP1]]
; CHECK-NEXT: [[GEP:%.*]] = getelementptr i8, ptr [[TMP2]], i64 40
; CHECK-NEXT: [[TMP2:%.*]] = getelementptr inbounds i32, ptr [[PTR]], i64 [[TMP1]]
; CHECK-NEXT: [[GEP:%.*]] = getelementptr inbounds i8, ptr [[TMP2]], i64 40
; CHECK-NEXT: ret ptr [[GEP]]
;
%a.nneg = icmp sgt i32 %a, -1
Expand Down