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Merged
merged 3 commits into from
Feb 21, 2025
Merged

Check for mutability better #127843

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7a919e2
Implement mutable check in Sema
DKLoehr Feb 20, 2025
2e9bafe
Add test
DKLoehr Feb 20, 2025
be54822
Make function static
DKLoehr Feb 21, 2025
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35 changes: 19 additions & 16 deletions clang/lib/Sema/SemaDecl.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -13440,6 +13440,23 @@ bool Sema::GloballyUniqueObjectMightBeAccidentallyDuplicated(
return true;
}

// Determine whether the object seems mutable for the purpose of diagnosing
// possible unique object duplication, i.e. non-const-qualified, and
// not an always-constant type like a function.
// Not perfect: doesn't account for mutable members, for example, or
// elements of container types.
// For nested pointers, any individual level being non-const is sufficient.
bool looksMutable(QualType T, const ASTContext &Ctx) {
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@zmodem zmodem Feb 20, 2025

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nit: make it static since it's local to this file

T = T.getNonReferenceType();
if (T->isFunctionType())
return false;
if (!T.isConstant(Ctx))
return true;
if (T->isPointerType())
return looksMutable(T->getPointeeType(), Ctx);
return false;
}

void Sema::DiagnoseUniqueObjectDuplication(const VarDecl *VD) {
// If this object has external linkage and hidden visibility, it might be
// duplicated when built into a shared library, which causes problems if it's
Expand All @@ -13454,24 +13471,10 @@ void Sema::DiagnoseUniqueObjectDuplication(const VarDecl *VD) {
!VD->isTemplated() &&
GloballyUniqueObjectMightBeAccidentallyDuplicated(VD)) {

// Check mutability. For pointers, ensure that both the pointer and the
// pointee are (recursively) const.
QualType Type = VD->getType().getNonReferenceType();
if (!Type.isConstant(VD->getASTContext())) {
QualType Type = VD->getType();
if (looksMutable(Type, VD->getASTContext())) {
Diag(VD->getLocation(), diag::warn_possible_object_duplication_mutable)
<< VD;
} else {
while (Type->isPointerType()) {
Type = Type->getPointeeType();
if (Type->isFunctionType())
break;
if (!Type.isConstant(VD->getASTContext())) {
Diag(VD->getLocation(),
diag::warn_possible_object_duplication_mutable)
<< VD;
break;
}
}
}

// To keep false positives low, only warn if we're certain that the
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3 changes: 3 additions & 0 deletions clang/test/SemaCXX/unique_object_duplication.h
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Expand Up @@ -99,6 +99,9 @@ inline void has_thread_local() {
thread_local int disallowedThreadLocal = 0; // hidden-warning {{'disallowedThreadLocal' may be duplicated when built into a shared library: it is mutable, has hidden visibility, and external linkage}}
}

// Functions themselves are always immutable, so referencing them is okay
inline auto& allowedFunctionReference = has_static_locals_external;

} // namespace StaticLocalTest

/******************************************************************************
Expand Down