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[TBAA] Refine pointer-tbaa for void pointers by pointer depth #126047

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Merged
merged 4 commits into from
Feb 20, 2025
Merged

[TBAA] Refine pointer-tbaa for void pointers by pointer depth #126047

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f516639
[TBAA] Refine pointer-tbaa for void pointers by pointer depth
brunodf-snps Feb 6, 2025
aa4ccd6
CodeGenTBAA: getAnyPtr: add extra comment describing AnyPtrs
brunodf-snps Feb 6, 2025
8068c5b
CodeGenTBAA: getTypeInfoHelper: also use pointer depth in conservativ…
brunodf-snps Feb 10, 2025
ffa0edc
CodeGenTBAA: getAnyPtr: further extend description in comment based o…
brunodf-snps Feb 11, 2025
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33 changes: 27 additions & 6 deletions clang/lib/CodeGen/CodeGenTBAA.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -80,6 +80,28 @@ llvm::MDNode *CodeGenTBAA::getChar() {
return Char;
}

llvm::MDNode *CodeGenTBAA::getAnyPtr(unsigned PtrDepth) {
assert(PtrDepth >= 1 && "Pointer must have some depth");

// Populate at least PtrDepth elements in AnyPtrs. These are the type nodes
// for "any" pointers of increasing pointer depth, and are organized in the
// hierarchy: any pointer <- any p2 pointer <- any p3 pointer <- ...
if (AnyPtrs.size() < PtrDepth) {
AnyPtrs.reserve(PtrDepth);
auto Size = Module.getDataLayout().getPointerSize();
// Populate first element.
if (AnyPtrs.empty())
AnyPtrs.push_back(createScalarTypeNode("any pointer", getChar(), Size));
// Populate further elements.
for (size_t Idx = AnyPtrs.size(); Idx < PtrDepth; ++Idx) {
auto Name = ("any p" + llvm::Twine(Idx + 1) + " pointer").str();
AnyPtrs.push_back(createScalarTypeNode(Name, AnyPtrs[Idx - 1], Size));
}
}

return AnyPtrs[PtrDepth - 1];
}

static bool TypeHasMayAlias(QualType QTy) {
// Tagged types have declarations, and therefore may have attributes.
if (auto *TD = QTy->getAsTagDecl())
Expand Down Expand Up @@ -202,9 +224,8 @@ llvm::MDNode *CodeGenTBAA::getTypeInfoHelper(const Type *Ty) {
// they involve a significant representation difference. We don't
// currently do so, however.
if (Ty->isPointerType() || Ty->isReferenceType()) {
llvm::MDNode *AnyPtr = createScalarTypeNode("any pointer", getChar(), Size);
if (!CodeGenOpts.PointerTBAA)
return AnyPtr;
return getAnyPtr();
// C++ [basic.lval]p11 permits objects to accessed through an l-value of
// similar type. Two types are similar under C++ [conv.qual]p2 if the
// decomposition of the types into pointers, member pointers, and arrays has
Expand Down Expand Up @@ -232,7 +253,7 @@ llvm::MDNode *CodeGenTBAA::getTypeInfoHelper(const Type *Ty) {
// common idioms and there is no good alternative to re-write the code
// without strict-aliasing violations.
if (Ty->isVoidType())
return AnyPtr;
return getAnyPtr(PtrDepth);

assert(!isa<VariableArrayType>(Ty));
// When the underlying type is a builtin type, we compute the pointee type
Expand All @@ -256,7 +277,7 @@ llvm::MDNode *CodeGenTBAA::getTypeInfoHelper(const Type *Ty) {
// similar-types rule.
const auto *RT = Ty->getAs<RecordType>();
if (!RT)
return AnyPtr;
return getAnyPtr();

// For unnamed structs or unions C's compatible types rule applies. Two
// compatible types in different compilation units can have different
Expand All @@ -270,7 +291,7 @@ llvm::MDNode *CodeGenTBAA::getTypeInfoHelper(const Type *Ty) {
// compatibility rule, but it doesn't matter because you can never have a
// pointer to an anonymous struct or union.
if (!RT->getDecl()->getDeclName())
return AnyPtr;
return getAnyPtr();

// For non-builtin types use the mangled name of the canonical type.
llvm::raw_svector_ostream TyOut(TyName);
Expand All @@ -281,7 +302,7 @@ llvm::MDNode *CodeGenTBAA::getTypeInfoHelper(const Type *Ty) {
OutName += std::to_string(PtrDepth);
OutName += " ";
OutName += TyName;
return createScalarTypeNode(OutName, AnyPtr, Size);
return createScalarTypeNode(OutName, getAnyPtr(PtrDepth), Size);
}

// Accesses to arrays are accesses to objects of their element types.
Expand Down
5 changes: 5 additions & 0 deletions clang/lib/CodeGen/CodeGenTBAA.h
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Expand Up @@ -139,6 +139,7 @@ class CodeGenTBAA {

llvm::MDNode *Root;
llvm::MDNode *Char;
llvm::SmallVector<llvm::MDNode *, 4> AnyPtrs;

/// getRoot - This is the mdnode for the root of the metadata type graph
/// for this translation unit.
Expand All @@ -148,6 +149,10 @@ class CodeGenTBAA {
/// considered to be equivalent to it.
llvm::MDNode *getChar();

/// getAnyPtr - This is the mdnode for any pointer type of (at least) the
/// given pointer depth.
llvm::MDNode *getAnyPtr(unsigned PtrDepth = 1);

/// CollectFields - Collect information about the fields of a type for
/// !tbaa.struct metadata formation. Return false for an unsupported type.
bool CollectFields(uint64_t BaseOffset,
Expand Down
3 changes: 2 additions & 1 deletion clang/test/CXX/drs/cwg158.cpp
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Expand Up @@ -42,5 +42,6 @@ const int * h(const int * (*p)[10], int *(*q)[9]) {
}

// POINTER-TBAA: [[PTRARRAY_TBAA]] = !{[[PTRARRAY_TY:!.+]], [[PTRARRAY_TY]], i64 0}
// POINTER-TBAA: [[PTRARRAY_TY]] = !{!"p2 int", [[ANYPTR:!.+]], i64 0}
// POINTER-TBAA: [[PTRARRAY_TY]] = !{!"p2 int", [[ANYP2PTR:!.+]], i64 0}
// POINTER-TBAA: [[ANYP2PTR]] = !{!"any p2 pointer", [[ANYPTR:!.+]],
// POINTER-TBAA: [[ANYPTR]] = !{!"any pointer"
22 changes: 14 additions & 8 deletions clang/test/CodeGen/tbaa-pointers.c
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Expand Up @@ -208,8 +208,10 @@ int void_ptrs(void **ptr) {
// COMMON-LABEL: define i32 @void_ptrs(
// COMMON-SAME: ptr noundef [[PTRA:%.+]])
// COMMON: [[PTR_ADDR:%.+]] = alloca ptr, align 8
// COMMON-NEXT: store ptr [[PTRA]], ptr [[PTR_ADDR]], align 8, !tbaa [[ANYPTR]]
// COMMON-NEXT: [[L0:%.+]] = load ptr, ptr [[PTR_ADDR]], align 8, !tbaa [[ANYPTR]]
// DISABLE-NEXT: store ptr [[PTRA]], ptr [[PTR_ADDR]], align 8, !tbaa [[ANYPTR]]
// DEFAULT-NEXT: store ptr [[PTRA]], ptr [[PTR_ADDR]], align 8, !tbaa [[ANYP2:!.+]]
// DISABLE-NEXT: [[L0:%.+]] = load ptr, ptr [[PTR_ADDR]], align 8, !tbaa [[ANYPTR]]
// DEFAULT-NEXT: [[L0:%.+]] = load ptr, ptr [[PTR_ADDR]], align 8, !tbaa [[ANYP2]]
// COMMON-NEXT: [[L1:%.+]] = load ptr, ptr [[L0]], align 8, !tbaa [[ANYPTR]]
// COMMON-NEXT: [[BOOL:%.+]] = icmp ne ptr [[L1]], null
// COMMON-NEXT: [[BOOL_EXT:%.+]] = zext i1 [[BOOL]] to i64
Expand All @@ -220,25 +222,28 @@ int void_ptrs(void **ptr) {
}

// DEFAULT: [[P2INT_0]] = !{[[P2INT:!.+]], [[P2INT]], i64 0}
// DEFAULT: [[P2INT]] = !{!"p2 int", [[ANY_POINTER:!.+]], i64 0}
// DEFAULT: [[P2INT]] = !{!"p2 int", [[ANY_P2_POINTER:!.+]], i64 0}
// DEFAULT: [[ANY_P2_POINTER]] = !{!"any p2 pointer", [[ANY_POINTER:!.+]], i64 0}
// DISABLE: [[ANYPTR]] = !{[[ANY_POINTER:!.+]], [[ANY_POINTER]], i64 0}
// COMMON: [[ANY_POINTER]] = !{!"any pointer", [[CHAR:!.+]], i64 0}
// COMMON: [[CHAR]] = !{!"omnipotent char", [[TBAA_ROOT:!.+]], i64 0}
// COMMON: [[TBAA_ROOT]] = !{!"Simple C/C++ TBAA"}
// DEFAULT: [[P1INT_0]] = !{[[P1INT:!.+]], [[P1INT]], i64 0}
// DEFAULT: [[P1INT]] = !{!"p1 int", [[ANY_POINTER]], i64 0}
// DEFAULT: [[P3INT_0]] = !{[[P3INT:!.+]], [[P3INT]], i64 0}
// DEFAULT: [[P3INT]] = !{!"p3 int", [[ANY_POINTER]], i64 0}
// DEFAULT: [[P3INT]] = !{!"p3 int", [[ANY_P3_POINTER:!.+]], i64 0}
// DEFAULT: [[ANY_P3_POINTER]] = !{!"any p3 pointer", [[ANY_P2_POINTER]], i64 0}
// DEFAULT: [[P4CHAR_0]] = !{[[P4CHAR:!.+]], [[P4CHAR]], i64 0}
// DEFAULT: [[P4CHAR]] = !{!"p4 omnipotent char", [[ANY_POINTER]], i64 0}
// DEFAULT: [[P4CHAR]] = !{!"p4 omnipotent char", [[ANY_P4_POINTER:!.*]], i64 0}
// DEFAULT: [[ANY_P4_POINTER]] = !{!"any p4 pointer", [[ANY_P3_POINTER]], i64 0}
// DEFAULT: [[P3CHAR_0]] = !{[[P3CHAR:!.+]], [[P3CHAR]], i64 0}
// DEFAULT: [[P3CHAR]] = !{!"p3 omnipotent char", [[ANY_POINTER]], i64 0}
// DEFAULT: [[P3CHAR]] = !{!"p3 omnipotent char", [[ANY_P3_POINTER]], i64 0}
// DEFAULT: [[P2CHAR_0]] = !{[[P2CHAR:!.+]], [[P2CHAR]], i64 0}
// DEFAULT: [[P2CHAR]] = !{!"p2 omnipotent char", [[ANY_POINTER]], i64 0}
// DEFAULT: [[P2CHAR]] = !{!"p2 omnipotent char", [[ANY_P2_POINTER]], i64 0}
// DEFAULT: [[P1CHAR_0]] = !{[[P1CHAR:!.+]], [[P1CHAR]], i64 0}
// DEFAULT: [[P1CHAR]] = !{!"p1 omnipotent char", [[ANY_POINTER]], i64 0}
// DEFAULT: [[P2S1_TAG]] = !{[[P2S1:!.+]], [[P2S1]], i64 0}
// DEFAULT: [[P2S1]] = !{!"p2 _ZTS2S1", [[ANY_POINTER]], i64 0}
// DEFAULT: [[P2S1]] = !{!"p2 _ZTS2S1", [[ANY_P2_POINTER]], i64 0}
// DEFAULT: [[P1S1_TAG:!.+]] = !{[[P1S1:!.+]], [[P1S1]], i64 0}
// DEFAULT: [[P1S1]] = !{!"p1 _ZTS2S1", [[ANY_POINTER]], i64 0}
// DEFAULT: [[P1S2_TAG]] = !{[[P1S2:!.+]], [[P1S2]], i64 0}
Expand All @@ -251,3 +256,4 @@ int void_ptrs(void **ptr) {
// COMMON: [[INT_TAG]] = !{[[INT_TY:!.+]], [[INT_TY]], i64 0}
// COMMON: [[INT_TY]] = !{!"int", [[CHAR]], i64 0}
// DEFAULT: [[ANYPTR]] = !{[[ANY_POINTER]], [[ANY_POINTER]], i64 0}
// DEFAULT: [[ANYP2]] = !{[[ANY_P2_POINTER]], [[ANY_P2_POINTER]], i64 0}