[llvm] 29555ad - [InstCombine] Improve inbounds preservation for ADD+GEP -> GEP+GEP (#135155)
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Mon Apr 14 02:03:10 PDT 2025
Author: Björn Pettersson
Date: 2025-04-14T11:03:06+02:00
New Revision: 29555ad5efea20308c7a5ee851a4cba9093a607d
URL: https://github.com/llvm/llvm-project/commit/29555ad5efea20308c7a5ee851a4cba9093a607d
DIFF: https://github.com/llvm/llvm-project/commit/29555ad5efea20308c7a5ee851a4cba9093a607d.diff
LOG: [InstCombine] Improve inbounds preservation for ADD+GEP -> GEP+GEP (#135155)
Given that we have a "add nuw" and a "getelementptr inbounds nuw" like
this:
%idx = add nuw i64 %idx1, %idx2
%gep = getelementptr inbounds nuw i32, ptr %ptr, i64 %idx
Then we can preserve the "inbounds nuw" flag when transforming that into
two getelementptr instructions:
%gep1 = getelementptr inbounds nuw i32, ptr %ptr, i64 %idx1
%gep = getelementptr inbounds nuw i32, ptr %ptr, i64 %idx2
Similarly for just having "nuw", and "nusw nuw" instead of "inbounds nuw"
on the getelementptr.
Proof: https://alive2.llvm.org/ce/z/QSweWW
Added:
Modified:
llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
llvm/test/Transforms/InstCombine/array.ll
Removed:
################################################################################
diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index 856e02c9f1ddb..48f9179d5eaab 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -3086,13 +3086,47 @@ Instruction *InstCombinerImpl::visitGetElementPtrInst(GetElementPtrInst &GEP) {
if (GEPType->isVectorTy())
return nullptr;
+ if (!GEP.isInBounds()) {
+ unsigned IdxWidth =
+ DL.getIndexSizeInBits(PtrOp->getType()->getPointerAddressSpace());
+ APInt BasePtrOffset(IdxWidth, 0);
+ Value *UnderlyingPtrOp =
+ PtrOp->stripAndAccumulateInBoundsConstantOffsets(DL, BasePtrOffset);
+ bool CanBeNull, CanBeFreed;
+ uint64_t DerefBytes = UnderlyingPtrOp->getPointerDereferenceableBytes(
+ DL, CanBeNull, CanBeFreed);
+ if (!CanBeNull && !CanBeFreed && DerefBytes != 0) {
+ if (GEP.accumulateConstantOffset(DL, BasePtrOffset) &&
+ BasePtrOffset.isNonNegative()) {
+ APInt AllocSize(IdxWidth, DerefBytes);
+ if (BasePtrOffset.ule(AllocSize)) {
+ return GetElementPtrInst::CreateInBounds(
+ GEP.getSourceElementType(), PtrOp, Indices, GEP.getName());
+ }
+ }
+ }
+ }
+
+ // nusw + nneg -> nuw
+ if (GEP.hasNoUnsignedSignedWrap() && !GEP.hasNoUnsignedWrap() &&
+ all_of(GEP.indices(), [&](Value *Idx) {
+ return isKnownNonNegative(Idx, SQ.getWithInstruction(&GEP));
+ })) {
+ GEP.setNoWrapFlags(GEP.getNoWrapFlags() | GEPNoWrapFlags::noUnsignedWrap());
+ return &GEP;
+ }
+
+ // These rewrites are trying to preserve inbounds/nuw attributes. So we want
+ // to do this after having tried to derive "nuw" above.
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);
+ // Given (gep p, x+y) we want to determine the common nowrap flags for both
+ // geps if transforming into (gep (gep p, x), y).
+ auto GetPreservedNoWrapFlags = [&](bool AddIsNUW) {
+ // We can preserve both "inbounds nuw", "nusw nuw" and "nuw" if we know
+ // that x + y does not have unsigned wrap.
+ if (GEP.hasNoUnsignedWrap() && AddIsNUW)
+ return GEP.getNoWrapFlags();
+ return GEPNoWrapFlags::none();
};
// Try to replace ADD + GEP with GEP + GEP.
@@ -3104,15 +3138,14 @@ Instruction *InstCombinerImpl::visitGetElementPtrInst(GetElementPtrInst &GEP) {
// as:
// %newptr = getelementptr i32, ptr %ptr, i64 %idx1
// %newgep = getelementptr i32, ptr %newptr, i64 %idx2
- bool IsInBounds = CanPreserveInBounds(
- cast<OverflowingBinaryOperator>(GEP.getOperand(1))->hasNoSignedWrap(),
- Idx1, Idx2);
+ bool NUW = match(GEP.getOperand(1), m_NUWAddLike(m_Value(), m_Value()));
+ GEPNoWrapFlags NWFlags = GetPreservedNoWrapFlags(NUW);
auto *NewPtr =
Builder.CreateGEP(GEP.getSourceElementType(), GEP.getPointerOperand(),
- Idx1, "", IsInBounds);
- return replaceInstUsesWith(
- GEP, Builder.CreateGEP(GEP.getSourceElementType(), NewPtr, Idx2, "",
- IsInBounds));
+ Idx1, "", NWFlags);
+ return replaceInstUsesWith(GEP,
+ Builder.CreateGEP(GEP.getSourceElementType(),
+ NewPtr, Idx2, "", NWFlags));
}
ConstantInt *C;
if (match(GEP.getOperand(1), m_OneUse(m_SExtLike(m_OneUse(m_NSWAdd(
@@ -3123,51 +3156,20 @@ 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);
+ bool NUW = match(GEP.getOperand(1),
+ m_NNegZExt(m_NUWAddLike(m_Value(), m_Value())));
+ GEPNoWrapFlags NWFlags = GetPreservedNoWrapFlags(NUW);
auto *NewPtr = Builder.CreateGEP(
GEP.getSourceElementType(), GEP.getPointerOperand(),
- Builder.CreateSExt(Idx1, GEP.getOperand(1)->getType()), "",
- IsInBounds);
+ Builder.CreateSExt(Idx1, GEP.getOperand(1)->getType()), "", NWFlags);
return replaceInstUsesWith(
GEP,
Builder.CreateGEP(GEP.getSourceElementType(), NewPtr,
Builder.CreateSExt(C, GEP.getOperand(1)->getType()),
- "", IsInBounds));
+ "", NWFlags));
}
}
- if (!GEP.isInBounds()) {
- unsigned IdxWidth =
- DL.getIndexSizeInBits(PtrOp->getType()->getPointerAddressSpace());
- APInt BasePtrOffset(IdxWidth, 0);
- Value *UnderlyingPtrOp =
- PtrOp->stripAndAccumulateInBoundsConstantOffsets(DL,
- BasePtrOffset);
- bool CanBeNull, CanBeFreed;
- uint64_t DerefBytes = UnderlyingPtrOp->getPointerDereferenceableBytes(
- DL, CanBeNull, CanBeFreed);
- if (!CanBeNull && !CanBeFreed && DerefBytes != 0) {
- if (GEP.accumulateConstantOffset(DL, BasePtrOffset) &&
- BasePtrOffset.isNonNegative()) {
- APInt AllocSize(IdxWidth, DerefBytes);
- if (BasePtrOffset.ule(AllocSize)) {
- return GetElementPtrInst::CreateInBounds(
- GEP.getSourceElementType(), PtrOp, Indices, GEP.getName());
- }
- }
- }
- }
-
- // nusw + nneg -> nuw
- if (GEP.hasNoUnsignedSignedWrap() && !GEP.hasNoUnsignedWrap() &&
- all_of(GEP.indices(), [&](Value *Idx) {
- return isKnownNonNegative(Idx, SQ.getWithInstruction(&GEP));
- })) {
- GEP.setNoWrapFlags(GEP.getNoWrapFlags() | GEPNoWrapFlags::noUnsignedWrap());
- return &GEP;
- }
-
if (Instruction *R = foldSelectGEP(GEP, Builder))
return R;
diff --git a/llvm/test/Transforms/InstCombine/array.ll b/llvm/test/Transforms/InstCombine/array.ll
index a09b66273368c..dd4725cfb1db3 100644
--- a/llvm/test/Transforms/InstCombine/array.ll
+++ b/llvm/test/Transforms/InstCombine/array.ll
@@ -122,12 +122,11 @@ define ptr @gep_inbounds_nuwaddlike(ptr %ptr, i64 %a, i64 %b) {
ret ptr %gep
}
-; FIXME: Preserve "inbounds nuw".
define ptr @gep_inbounds_add_nuw(ptr %ptr, i64 %a, i64 %b) {
; CHECK-LABEL: define ptr @gep_inbounds_add_nuw(
; CHECK-SAME: ptr [[PTR:%.*]], i64 [[A:%.*]], i64 [[B:%.*]]) {
-; CHECK-NEXT: [[TMP1:%.*]] = getelementptr i32, ptr [[PTR]], i64 [[A]]
-; CHECK-NEXT: [[GEP:%.*]] = getelementptr i32, ptr [[TMP1]], i64 [[B]]
+; CHECK-NEXT: [[TMP1:%.*]] = getelementptr inbounds nuw i32, ptr [[PTR]], i64 [[A]]
+; CHECK-NEXT: [[GEP:%.*]] = getelementptr inbounds nuw i32, ptr [[TMP1]], i64 [[B]]
; CHECK-NEXT: ret ptr [[GEP]]
;
%add = add nuw i64 %a, %b
@@ -135,12 +134,11 @@ define ptr @gep_inbounds_add_nuw(ptr %ptr, i64 %a, i64 %b) {
ret ptr %gep
}
-; FIXME: Preserve "nusw nuw".
define ptr @gep_inbounds_add_nusw_nuw(ptr %ptr, i64 %a, i64 %b) {
; CHECK-LABEL: define ptr @gep_inbounds_add_nusw_nuw(
; CHECK-SAME: ptr [[PTR:%.*]], i64 [[A:%.*]], i64 [[B:%.*]]) {
-; CHECK-NEXT: [[TMP1:%.*]] = getelementptr i32, ptr [[PTR]], i64 [[A]]
-; CHECK-NEXT: [[GEP:%.*]] = getelementptr i32, ptr [[TMP1]], i64 [[B]]
+; CHECK-NEXT: [[TMP1:%.*]] = getelementptr nusw nuw i32, ptr [[PTR]], i64 [[A]]
+; CHECK-NEXT: [[GEP:%.*]] = getelementptr nusw nuw i32, ptr [[TMP1]], i64 [[B]]
; CHECK-NEXT: ret ptr [[GEP]]
;
%add = add nuw i64 %a, %b
@@ -148,12 +146,11 @@ define ptr @gep_inbounds_add_nusw_nuw(ptr %ptr, i64 %a, i64 %b) {
ret ptr %gep
}
-; FIXME: Preserve "nuw".
define ptr @gep_add_nuw(ptr %ptr, i64 %a, i64 %b) {
; CHECK-LABEL: define ptr @gep_add_nuw(
; CHECK-SAME: ptr [[PTR:%.*]], i64 [[A:%.*]], i64 [[B:%.*]]) {
-; CHECK-NEXT: [[TMP1:%.*]] = getelementptr i32, ptr [[PTR]], i64 [[A]]
-; CHECK-NEXT: [[GEP:%.*]] = getelementptr i32, ptr [[TMP1]], i64 [[B]]
+; CHECK-NEXT: [[TMP1:%.*]] = getelementptr nuw i32, ptr [[PTR]], i64 [[A]]
+; CHECK-NEXT: [[GEP:%.*]] = getelementptr nuw i32, ptr [[TMP1]], i64 [[B]]
; CHECK-NEXT: ret ptr [[GEP]]
;
%add = add nuw i64 %a, %b
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