[clang] Emit nuw GEPs for array subscript expressions #103088
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Generate nuw GEPs for array subscript expressions where the base address points to the base of a constant size array and the index is unsigned.
llvmbot
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clang
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@llvm/pr-subscribers-clang-codegen @llvm/pr-subscribers-clang Author: Hari Limaye (hazzlim) ChangesGenerate nuw GEPs for array subscript expressions where the base address points to the base of a constant size array and the index is unsigned. Patch is 20.26 KiB, truncated to 20.00 KiB below, full version: https://github.com/llvm/llvm-project/pull/103088.diff 7 Files Affected:
diff --git a/clang/lib/CodeGen/CGBuilder.h b/clang/lib/CodeGen/CGBuilder.h
index 08730a6a6672a1..b8036cf6e6a306 100644
--- a/clang/lib/CodeGen/CGBuilder.h
+++ b/clang/lib/CodeGen/CGBuilder.h
@@ -14,6 +14,7 @@
#include "CodeGenTypeCache.h"
#include "llvm/Analysis/Utils/Local.h"
#include "llvm/IR/DataLayout.h"
+#include "llvm/IR/GEPNoWrapFlags.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/Type.h"
@@ -334,9 +335,10 @@ class CGBuilderTy : public CGBuilderBaseTy {
Address CreateGEP(Address Addr, ArrayRef<llvm::Value *> IdxList,
llvm::Type *ElementType, CharUnits Align,
- const Twine &Name = "") {
+ const Twine &Name = "",
+ llvm::GEPNoWrapFlags NW = llvm::GEPNoWrapFlags::none()) {
llvm::Value *Ptr = emitRawPointerFromAddress(Addr);
- return RawAddress(CreateGEP(Addr.getElementType(), Ptr, IdxList, Name),
+ return RawAddress(CreateGEP(Addr.getElementType(), Ptr, IdxList, Name, NW),
ElementType, Align);
}
diff --git a/clang/lib/CodeGen/CGExpr.cpp b/clang/lib/CodeGen/CGExpr.cpp
index f93f8dda0bd29a..74fa7594baeb9e 100644
--- a/clang/lib/CodeGen/CGExpr.cpp
+++ b/clang/lib/CodeGen/CGExpr.cpp
@@ -3959,13 +3959,13 @@ static llvm::Value *emitArraySubscriptGEP(CodeGenFunction &CGF,
static Address emitArraySubscriptGEP(CodeGenFunction &CGF, Address addr,
ArrayRef<llvm::Value *> indices,
llvm::Type *elementType, bool inbounds,
- bool signedIndices, SourceLocation loc,
- CharUnits align,
+ bool nuw, bool signedIndices,
+ SourceLocation loc, CharUnits align,
const llvm::Twine &name = "arrayidx") {
if (inbounds) {
return CGF.EmitCheckedInBoundsGEP(addr, indices, elementType, signedIndices,
CodeGenFunction::NotSubtraction, loc,
- align, name);
+ align, name, nuw);
} else {
return CGF.Builder.CreateGEP(addr, indices, elementType, align, name);
}
@@ -4060,7 +4060,7 @@ static bool IsPreserveAIArrayBase(CodeGenFunction &CGF, const Expr *ArrayBase) {
static Address emitArraySubscriptGEP(CodeGenFunction &CGF, Address addr,
ArrayRef<llvm::Value *> indices,
- QualType eltType, bool inbounds,
+ QualType eltType, bool inbounds, bool nuw,
bool signedIndices, SourceLocation loc,
QualType *arrayType = nullptr,
const Expr *Base = nullptr,
@@ -4091,7 +4091,7 @@ static Address emitArraySubscriptGEP(CodeGenFunction &CGF, Address addr,
if (!LastIndex ||
(!CGF.IsInPreservedAIRegion && !IsPreserveAIArrayBase(CGF, Base))) {
addr = emitArraySubscriptGEP(CGF, addr, indices,
- CGF.ConvertTypeForMem(eltType), inbounds,
+ CGF.ConvertTypeForMem(eltType), inbounds, nuw,
signedIndices, loc, eltAlign, name);
return addr;
} else {
@@ -4214,7 +4214,7 @@ LValue CodeGenFunction::EmitArraySubscriptExpr(const ArraySubscriptExpr *E,
QualType EltType = LV.getType()->castAs<VectorType>()->getElementType();
Addr = emitArraySubscriptGEP(*this, Addr, Idx, EltType, /*inbounds*/ true,
- SignedIndices, E->getExprLoc());
+ /*nuw=*/false, SignedIndices, E->getExprLoc());
return MakeAddrLValue(Addr, EltType, LV.getBaseInfo(),
CGM.getTBAAInfoForSubobject(LV, EltType));
}
@@ -4245,7 +4245,7 @@ LValue CodeGenFunction::EmitArraySubscriptExpr(const ArraySubscriptExpr *E,
Addr = emitArraySubscriptGEP(*this, Addr, Idx, vla->getElementType(),
!getLangOpts().isSignedOverflowDefined(),
- SignedIndices, E->getExprLoc());
+ /*nuw=*/false, SignedIndices, E->getExprLoc());
} else if (const ObjCObjectType *OIT = E->getType()->getAs<ObjCObjectType>()){
// Indexing over an interface, as in "NSString *P; P[4];"
@@ -4332,10 +4332,20 @@ LValue CodeGenFunction::EmitArraySubscriptExpr(const ArraySubscriptExpr *E,
// Propagate the alignment from the array itself to the result.
QualType arrayType = Array->getType();
- Addr = emitArraySubscriptGEP(
- *this, ArrayLV.getAddress(), {CGM.getSize(CharUnits::Zero()), Idx},
- E->getType(), !getLangOpts().isSignedOverflowDefined(), SignedIndices,
- E->getExprLoc(), &arrayType, E->getBase());
+
+ bool Inbounds = !getLangOpts().isSignedOverflowDefined();
+ // (ISO/IEC 9899:TC3, 6.5.6.8) / (C++ expr.add 4.2)
+ // If A in A[i] is the base of a constant size array, then the addition of
+ // the index to the base pointer cannot wrap in an unsigned sense without
+ // violating the inbounds constraint.
+ bool NUW = !SignedIndices && Inbounds &&
+ (getLangOpts().C99 || getLangOpts().CPlusPlus) &&
+ getContext().getAsConstantArrayType(arrayType);
+
+ Addr = emitArraySubscriptGEP(*this, ArrayLV.getAddress(),
+ {CGM.getSize(CharUnits::Zero()), Idx},
+ E->getType(), Inbounds, NUW, SignedIndices,
+ E->getExprLoc(), &arrayType, E->getBase());
EltBaseInfo = ArrayLV.getBaseInfo();
EltTBAAInfo = CGM.getTBAAInfoForSubobject(ArrayLV, E->getType());
} else {
@@ -4345,8 +4355,8 @@ LValue CodeGenFunction::EmitArraySubscriptExpr(const ArraySubscriptExpr *E,
QualType ptrType = E->getBase()->getType();
Addr = emitArraySubscriptGEP(*this, Addr, Idx, E->getType(),
!getLangOpts().isSignedOverflowDefined(),
- SignedIndices, E->getExprLoc(), &ptrType,
- E->getBase());
+ /*nuw=*/false, SignedIndices, E->getExprLoc(),
+ &ptrType, E->getBase());
}
LValue LV = MakeAddrLValue(Addr, E->getType(), EltBaseInfo, EltTBAAInfo);
@@ -4543,6 +4553,7 @@ LValue CodeGenFunction::EmitArraySectionExpr(const ArraySectionExpr *E,
Idx = Builder.CreateNSWMul(Idx, NumElements);
EltPtr = emitArraySubscriptGEP(*this, Base, Idx, VLA->getElementType(),
!getLangOpts().isSignedOverflowDefined(),
+ /*nuw=*/false,
/*signedIndices=*/false, E->getExprLoc());
} else if (const Expr *Array = isSimpleArrayDecayOperand(E->getBase())) {
// If this is A[i] where A is an array, the frontend will have decayed the
@@ -4563,6 +4574,7 @@ LValue CodeGenFunction::EmitArraySectionExpr(const ArraySectionExpr *E,
EltPtr = emitArraySubscriptGEP(
*this, ArrayLV.getAddress(), {CGM.getSize(CharUnits::Zero()), Idx},
ResultExprTy, !getLangOpts().isSignedOverflowDefined(),
+ /*nuw=*/false,
/*signedIndices=*/false, E->getExprLoc());
BaseInfo = ArrayLV.getBaseInfo();
TBAAInfo = CGM.getTBAAInfoForSubobject(ArrayLV, ResultExprTy);
@@ -4572,7 +4584,8 @@ LValue CodeGenFunction::EmitArraySectionExpr(const ArraySectionExpr *E,
ResultExprTy, IsLowerBound);
EltPtr = emitArraySubscriptGEP(*this, Base, Idx, ResultExprTy,
!getLangOpts().isSignedOverflowDefined(),
- /*signedIndices=*/false, E->getExprLoc());
+ /*signedIndices=*/false, /*nuw=*/false,
+ E->getExprLoc());
}
return MakeAddrLValue(EltPtr, ResultExprTy, BaseInfo, TBAAInfo);
diff --git a/clang/lib/CodeGen/CGExprScalar.cpp b/clang/lib/CodeGen/CGExprScalar.cpp
index 84392745ea6144..c9014cb68b06eb 100644
--- a/clang/lib/CodeGen/CGExprScalar.cpp
+++ b/clang/lib/CodeGen/CGExprScalar.cpp
@@ -35,6 +35,7 @@
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/FixedPointBuilder.h"
#include "llvm/IR/Function.h"
+#include "llvm/IR/GEPNoWrapFlags.h"
#include "llvm/IR/GetElementPtrTypeIterator.h"
#include "llvm/IR/GlobalVariable.h"
#include "llvm/IR/Intrinsics.h"
@@ -5713,13 +5714,18 @@ static GEPOffsetAndOverflow EmitGEPOffsetInBytes(Value *BasePtr, Value *GEPVal,
return {TotalOffset, OffsetOverflows};
}
-Value *
-CodeGenFunction::EmitCheckedInBoundsGEP(llvm::Type *ElemTy, Value *Ptr,
- ArrayRef<Value *> IdxList,
- bool SignedIndices, bool IsSubtraction,
- SourceLocation Loc, const Twine &Name) {
+Value *CodeGenFunction::EmitCheckedInBoundsGEP(llvm::Type *ElemTy, Value *Ptr,
+ ArrayRef<Value *> IdxList,
+ bool SignedIndices,
+ bool IsSubtraction,
+ SourceLocation Loc,
+ const Twine &Name, bool NUW) {
llvm::Type *PtrTy = Ptr->getType();
- Value *GEPVal = Builder.CreateInBoundsGEP(ElemTy, Ptr, IdxList, Name);
+
+ llvm::GEPNoWrapFlags NWFlags = llvm::GEPNoWrapFlags::inBounds();
+ if (NUW)
+ NWFlags |= llvm::GEPNoWrapFlags::noUnsignedWrap();
+ Value *GEPVal = Builder.CreateGEP(ElemTy, Ptr, IdxList, Name, NWFlags);
// If the pointer overflow sanitizer isn't enabled, do nothing.
if (!SanOpts.has(SanitizerKind::PointerOverflow))
@@ -5833,12 +5839,16 @@ CodeGenFunction::EmitCheckedInBoundsGEP(llvm::Type *ElemTy, Value *Ptr,
Address CodeGenFunction::EmitCheckedInBoundsGEP(
Address Addr, ArrayRef<Value *> IdxList, llvm::Type *elementType,
bool SignedIndices, bool IsSubtraction, SourceLocation Loc, CharUnits Align,
- const Twine &Name) {
- if (!SanOpts.has(SanitizerKind::PointerOverflow))
- return Builder.CreateInBoundsGEP(Addr, IdxList, elementType, Align, Name);
-
- return RawAddress(
- EmitCheckedInBoundsGEP(Addr.getElementType(), Addr.emitRawPointer(*this),
- IdxList, SignedIndices, IsSubtraction, Loc, Name),
- elementType, Align);
+ const Twine &Name, bool NUW) {
+ if (!SanOpts.has(SanitizerKind::PointerOverflow)) {
+ llvm::GEPNoWrapFlags NWFlags = llvm::GEPNoWrapFlags::inBounds();
+ if (NUW)
+ NWFlags |= llvm::GEPNoWrapFlags::noUnsignedWrap();
+ return Builder.CreateGEP(Addr, IdxList, elementType, Align, Name, NWFlags);
+ }
+
+ return RawAddress(EmitCheckedInBoundsGEP(
+ Addr.getElementType(), Addr.emitRawPointer(*this),
+ IdxList, SignedIndices, IsSubtraction, Loc, Name, NUW),
+ elementType, Align);
}
diff --git a/clang/lib/CodeGen/CodeGenFunction.h b/clang/lib/CodeGen/CodeGenFunction.h
index 19a7feeb69d820..f5aa8606e06323 100644
--- a/clang/lib/CodeGen/CodeGenFunction.h
+++ b/clang/lib/CodeGen/CodeGenFunction.h
@@ -5057,17 +5057,18 @@ class CodeGenFunction : public CodeGenTypeCache {
/// \p SignedIndices indicates whether any of the GEP indices are signed.
/// \p IsSubtraction indicates whether the expression used to form the GEP
/// is a subtraction.
+ /// \p NUW indicates whether the GEP is nuw.
llvm::Value *EmitCheckedInBoundsGEP(llvm::Type *ElemTy, llvm::Value *Ptr,
ArrayRef<llvm::Value *> IdxList,
- bool SignedIndices,
- bool IsSubtraction,
+ bool SignedIndices, bool IsSubtraction,
SourceLocation Loc,
- const Twine &Name = "");
+ const Twine &Name = "", bool NUW = false);
Address EmitCheckedInBoundsGEP(Address Addr, ArrayRef<llvm::Value *> IdxList,
llvm::Type *elementType, bool SignedIndices,
bool IsSubtraction, SourceLocation Loc,
- CharUnits Align, const Twine &Name = "");
+ CharUnits Align, const Twine &Name = "",
+ bool NUW = false);
/// Specifies which type of sanitizer check to apply when handling a
/// particular builtin.
diff --git a/clang/test/CodeGen/PowerPC/ppc-emmintrin.c b/clang/test/CodeGen/PowerPC/ppc-emmintrin.c
index a3650beec625f2..4c4d0dfce05eaf 100644
--- a/clang/test/CodeGen/PowerPC/ppc-emmintrin.c
+++ b/clang/test/CodeGen/PowerPC/ppc-emmintrin.c
@@ -1012,14 +1012,14 @@ test_shuffle() {
// CHECK: %[[SHR:[0-9a-zA-Z_.]+]] = ashr i32 %{{[0-9a-zA-Z_.]+}}, 6
// CHECK: %[[AND4:[0-9a-zA-Z_.]+]] = and i32 %[[SHR]], 3
// CHECK: sext i32 %[[AND4]] to i64
-// CHECK: getelementptr inbounds [4 x i32], ptr @_mm_shuffle_epi32.__permute_selectors, i64 0, i64 %{{[0-9a-zA-Z_.]+}}
+// CHECK: getelementptr inbounds nuw [4 x i32], ptr @_mm_shuffle_epi32.__permute_selectors, i64 0, i64 %{{[0-9a-zA-Z_.]+}}
// CHECK: insertelement <4 x i32> %{{[0-9a-zA-Z_.]+}}, i32 %{{[0-9a-zA-Z_.]+}}, i32 0
-// CHECK: getelementptr inbounds [4 x i32], ptr @_mm_shuffle_epi32.__permute_selectors, i64 0, i64 %{{[0-9a-zA-Z_.]+}}
+// CHECK: getelementptr inbounds nuw [4 x i32], ptr @_mm_shuffle_epi32.__permute_selectors, i64 0, i64 %{{[0-9a-zA-Z_.]+}}
// CHECK: insertelement <4 x i32> %{{[0-9a-zA-Z_.]+}}, i32 %{{[0-9a-zA-Z_.]+}}, i32 1
-// CHECK: getelementptr inbounds [4 x i32], ptr @_mm_shuffle_epi32.__permute_selectors, i64 0, i64 %{{[0-9a-zA-Z_.]+}}
+// CHECK: getelementptr inbounds nuw [4 x i32], ptr @_mm_shuffle_epi32.__permute_selectors, i64 0, i64 %{{[0-9a-zA-Z_.]+}}
// CHECK: %[[ADD:[0-9a-zA-Z_.]+]] = add i32 %{{[0-9a-zA-Z_.]+}}, 269488144
// CHECK: insertelement <4 x i32> %{{[0-9a-zA-Z_.]+}}, i32 %[[ADD]], i32 2
-// CHECK: getelementptr inbounds [4 x i32], ptr @_mm_shuffle_epi32.__permute_selectors, i64 0, i64 %{{[0-9a-zA-Z_.]+}}
+// CHECK: getelementptr inbounds nuw [4 x i32], ptr @_mm_shuffle_epi32.__permute_selectors, i64 0, i64 %{{[0-9a-zA-Z_.]+}}
// CHECK: add i32 %{{[0-9a-zA-Z_.]+}}, 269488144
// CHECK: call <4 x i32> @vec_perm(int vector[4], int vector[4], unsigned char vector[16])
@@ -1050,7 +1050,7 @@ test_shuffle() {
// CHECK: sext i32 %[[AND4]] to i64
// CHECK-LE: store <2 x i64> <i64 1663540288323457296, i64 0>, ptr %{{[0-9a-zA-Z_.]+}}, align 16
// CHECK-BE: store <2 x i64> <i64 1157726452361532951, i64 0>, ptr %{{[0-9a-zA-Z_.]+}}, align 16
-// CHECK-COUNT-4: getelementptr inbounds [4 x i16], ptr @_mm_shufflehi_epi16.__permute_selectors, i64 0, i64 {{[0-9a-zA-Z_%.]+}}
+// CHECK-COUNT-4: getelementptr inbounds nuw [4 x i16], ptr @_mm_shufflehi_epi16.__permute_selectors, i64 0, i64 {{[0-9a-zA-Z_%.]+}}
// CHECK: call <2 x i64> @vec_perm(unsigned long long vector[2], unsigned long long vector[2], unsigned char vector[16])
// CHECK-LABEL: define available_externally <2 x i64> @_mm_shufflelo_epi16
@@ -1067,7 +1067,7 @@ test_shuffle() {
// CHECK: sext i32 %[[AND4]] to i64
// CHECK-LE: store <2 x i64> <i64 0, i64 2242261671028070680>, ptr %{{[0-9a-zA-Z_.]+}}, align 16
// CHECK-BE: store <2 x i64> <i64 0, i64 1736447835066146335>, ptr %{{[0-9a-zA-Z_.]+}}, align 16
-// CHECK-COUNT-4: getelementptr inbounds [4 x i16], ptr @_mm_shufflelo_epi16.__permute_selectors, i64 0, i64 {{[0-9a-zA-Z_%.]+}}
+// CHECK-COUNT-4: getelementptr inbounds nuw [4 x i16], ptr @_mm_shufflelo_epi16.__permute_selectors, i64 0, i64 {{[0-9a-zA-Z_%.]+}}
// CHECK: call <2 x i64> @vec_perm(unsigned long long vector[2], unsigned long long vector[2], unsigned char vector[16])
void __attribute__((noinline))
diff --git a/clang/test/CodeGen/PowerPC/ppc-xmmintrin.c b/clang/test/CodeGen/PowerPC/ppc-xmmintrin.c
index 95dfd1202f1575..4a15fa9f76ceea 100644
--- a/clang/test/CodeGen/PowerPC/ppc-xmmintrin.c
+++ b/clang/test/CodeGen/PowerPC/ppc-xmmintrin.c
@@ -894,16 +894,16 @@ test_shuffle() {
// CHECK: %[[SHR3:[0-9a-zA-Z_.]+]] = ashr i32 %{{[0-9a-zA-Z_.]+}}, 6
// CHECK: %[[AND4:[0-9a-zA-Z_.]+]] = and i32 %[[SHR3]], 3
// CHECK: sext i32 %[[AND4]] to i64
-// CHECK: getelementptr inbounds [4 x i16], ptr @_mm_shuffle_pi16.__permute_selectors, i64 0, i64 %{{[0-9a-zA-Z_.]+}}
+// CHECK: getelementptr inbounds nuw [4 x i16], ptr @_mm_shuffle_pi16.__permute_selectors, i64 0, i64 %{{[0-9a-zA-Z_.]+}}
// CHECK-LE: getelementptr inbounds [4 x i16], ptr %{{[0-9a-zA-Z_.]+}}, i64 0, i64 0
// CHECK-BE: getelementptr inbounds [4 x i16], ptr %{{[0-9a-zA-Z_.]+}}, i64 0, i64 3
-// CHECK: getelementptr inbounds [4 x i16], ptr @_mm_shuffle_pi16.__permute_selectors, i64 0, i64 %{{[0-9a-zA-Z_.]+}}
+// CHECK: getelementptr inbounds nuw [4 x i16], ptr @_mm_shuffle_pi16.__permute_selectors, i64 0, i64 %{{[0-9a-zA-Z_.]+}}
// CHECK-LE: getelementptr inbounds [4 x i16], ptr %{{[0-9a-zA-Z_.]+}}, i64 0, i64 1
// CHECK-BE: getelementptr inbounds [4 x i16], ptr %{{[0-9a-zA-Z_.]+}}, i64 0, i64 2
-// CHECK: getelementptr inbounds [4 x i16], ptr @_mm_shuffle_pi16.__permute_selectors, i64 0, i64 %{{[0-9a-zA-Z_.]+}}
+// CHECK: getelementptr inbounds nuw [4 x i16], ptr @_mm_shuffle_pi16.__permute_selectors, i64 0, i64 %{{[0-9a-zA-Z_.]+}}
// CHECK-LE: getelementptr inbounds [4 x i16], ptr %{{[0-9a-zA-Z_.]+}}, i64 0, i64 2
// CHECK-BE: getelementptr inbounds [4 x i16], ptr %{{[0-9a-zA-Z_.]+}}, i64 0, i64 1
-// CHECK: getelementptr inbounds [4 x i16], ptr @_mm_shuffle_pi16.__permute_selectors, i64 0, i64 %{{[0-9a-zA-Z_.]+}}
+// CHECK: getelementptr inbounds nuw [4 x i16], ptr @_mm_shuffle_pi16.__permute_selectors, i64 0, i64 %{{[0-9a-zA-Z_.]+}}
// CHECK-LE: getelementptr inbounds [4 x i16], ptr %{{[0-9a-zA-Z_.]+}}, i64 0, i64 3
// CHECK-BE: getelementptr inbounds [4 x i16], ptr %{{[0-9a-zA-Z_.]+}}, i64 0, i64 0
// CHECK: call <2 x i64> @vec_splats(unsigned long long)
@@ -923,14 +923,14 @@ test_shuffle() {
// CHECK: %[[SHR3:[0-9a-zA-Z_.]+]] = ashr i32 %{{[0-9a-zA-Z_.]+}}, 6
// CHECK: %[[AND4:[0-9a-zA-Z_.]+]] = and i32 %[[SHR3]], 3
// CHECK: sext i32 %[[AND4]] to i64
-// CHECK: getelementptr inbounds [4 x i32], ptr @_mm_shuffle_ps.__permute_selectors, i64 0, i64
+// CHECK: getelementptr inbounds nuw [4 x i32], ptr @_mm_shuffle_ps.__permute_selectors, i64 0, i64
// CHECK: insertelement <4 x i32> %{{[0-9a-zA-Z_.]+}}, i32 %{{[0-9a-zA-Z_.]+}}, i32 0
-// CHECK: getelementptr inbounds [4 x i32], ptr @_mm_shuffle_ps.__permute_selectors, i64 0, i64
+// CHECK: getelementptr inbounds nuw [4 x i32], ptr @_mm_shuffle_ps.__permute_selectors, i64 0, i64
// CHECK: insertelement <4 x i32> %{{[0-9a-zA-Z_.]+}}, i32 %{{[0-9a-zA-Z_.]+}}, i32 1
-// CHECK: getelementptr inbounds [4 x i32], ptr @_mm_shuffle_ps.__permute_selectors, i64 0, i64
+// CHECK: getelementptr inbounds nuw [4 x i32], ptr @_mm_shuffle_ps.__permute_selectors, i64 0, i64
// CHECK: %[[ADD:[0-9a-zA-Z_.]+]] = add i32 %{{[0-9a-zA-Z_.]+}}, 269488144
// CHECK: insertelement <4 x i32> %{{[0-9a-zA-Z_.]+}}, i32 %[[ADD]], i32 2
-// CHECK: getelementptr inbounds [4 x i32], ptr @_mm_shuffle_ps.__permute_selectors, i64 0, i64
+// CHECK: getelementptr inbounds nuw [4 x i32], ptr @_mm_shuffle_ps.__permute_selectors, i64 0, i64
// CHECK: %[[ADD2:[0-9a-zA-Z_.]+]] = add i32 %{{[0-9a-zA-Z_.]+}}, 269488144
// CHECK: insertelement <4 x i32> %{{[0-9a-zA-Z_.]+}}, i32 %[[ADD2]], i32 3
// CHECK: call <4 x float> @vec_perm(float vector[4], float vector[4], unsigned char vector[16])
diff --git a/clang/test/CodeGenCXX/pr45964-decomp-transform.cpp b/clang/test/CodeGenCXX/pr45964-decomp-transform.cpp
index f7df110ec01298..bcb2d875dce663 100644
--- a/clang/test/CodeGenCXX/pr45964-decomp-transform.cpp
+++ b/clang/test/CodeGenCXX/pr45964-decomp-transform.cpp
@@ -16,7 +16,7 @@ void (*d)(){test_transform<0>};
// CHECK-NEXT: [[BODY]]:
// CHECK-NEXT: [[CUR:%.*]] = phi i64 [ 0, %[[ENTRY]] ], [ [[NEXT:%.*]], %[[BODY]] ]
// CHECK-NEXT: [[DEST:%.*]] = getelementptr inbounds i32, ptr [[BEGIN]], i64 [[CUR]]
-// CHECK-NEXT: [[SRC:%.*]] = getelementptr inbounds [1 x i32], ptr @...
[truncated]
|
|
This seems correct from my reading of the relevant parts of the C/C++ standard, regarding pointer arithmetic and array subscript expressions. It does actually seem like the restriction to unsigned indices here is actually unnecessary, and adding |
I don't understand how you think this would work; a-1 and a+-1 are required to produce the same result. |
nikic
reviewed
Aug 14, 2024
There was a problem hiding this comment.
As a high level comment: Do we need to pass through the nuw flag, rather than deriving it from signedIndices?
Basically, I think that we should be emitting nuw if and only if -fsanitize=undefined would perform a check for unsigned overflow for that gep, and the information to determine whether that is done should already be available in the relevant places.
(Unless we currently perform incorrect sanitizer checks in some cases -- in which case that needs to be fixed.)
| SignedIndices, E->getExprLoc(), &ptrType, | ||
| E->getBase()); | ||
| /*nuw=*/false, SignedIndices, E->getExprLoc(), | ||
| &ptrType, E->getBase()); |
There was a problem hiding this comment.
Why is the handling for arrays and pointers here different? Aren't they essentially semantically equivalent?
Abandoning this PR in favor of taking this approach in #105496 |
The thinking here RE signed indices was that in this special case, where the base address of the GEP is the start of an array, the index cannot be negative without violating the I wonder if others agree that this is valid or can see an issue with this? |
|
Oh, I see. If you can prove that it would be illegal to use a negative index with a particular pointer, you might be able to optimize... but I'm not sure how aggressive we want to be here. Even if the C standard technically disallows indexing past the beginning/end of a member array, it's not something we've historically checked or optimized, so it's likely to break code. |
|
Can this be closed in favor of #105496? |
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Generate nuw GEPs for array subscript expressions where the base address points to the base of a constant size array and the index is unsigned.