This revision was landed with ongoing or failed builds.
This revision was automatically updated to reflect the committed changes.
Closed by commit rG31b0be4eba9e: [Clang] Add lifetimebound attribute to
std::move/std::forward (authored by alexander-shaposhnikov).
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D141744/new/
https://reviews.llvm.org/D141744
Files:
clang/docs/LanguageExtensions.rst
clang/docs/ReleaseNotes.rst
clang/lib/Sema/SemaDecl.cpp
clang/test/SemaCXX/attr-lifetimebound.cpp
clang/test/SemaCXX/builtin-std-move.cpp
clang/test/SemaCXX/builtins.cpp
Index: clang/test/SemaCXX/builtins.cpp
===================================================================
--- clang/test/SemaCXX/builtins.cpp
+++ clang/test/SemaCXX/builtins.cpp
@@ -40,7 +40,7 @@
struct U { int n : 5; } u;
int *pbf = __builtin_addressof(u.n); // expected-error {{address of bit-field requested}}
- S *ptmp = __builtin_addressof(S{}); // expected-error {{taking the address of a temporary}}
+ S *ptmp = __builtin_addressof(S{}); // expected-error {{taking the address of a temporary}} expected-warning {{temporary whose address is used as value of local variable 'ptmp' will be destroyed at the end of the full-expression}}
}
namespace function_start {
Index: clang/test/SemaCXX/builtin-std-move.cpp
===================================================================
--- clang/test/SemaCXX/builtin-std-move.cpp
+++ clang/test/SemaCXX/builtin-std-move.cpp
@@ -85,7 +85,7 @@
A &forward_rval_as_lval() {
std::forward<A&&>(A()); // expected-warning {{const attribute}}
- return std::forward<A&>(A()); // expected-note {{instantiation of}}
+ return std::forward<A&>(A()); // expected-note {{instantiation of}} expected-warning {{returning reference}}
}
struct B {};
Index: clang/test/SemaCXX/attr-lifetimebound.cpp
===================================================================
--- clang/test/SemaCXX/attr-lifetimebound.cpp
+++ clang/test/SemaCXX/attr-lifetimebound.cpp
@@ -113,3 +113,77 @@
std::map<std::string, std::string> m;
const std::string &v = findOrDefault(m, "foo"s, "bar"s); // expected-warning {{temporary bound to local reference 'v'}}
}
+
+// definitions for std::move, std::forward et al.
+namespace std {
+inline namespace foo {
+
+template <class T> struct remove_reference {
+ typedef T type;
+};
+template <class T> struct remove_reference<T &> {
+ typedef T type;
+};
+template <class T> struct remove_reference<T &&> {
+ typedef T type;
+};
+
+template <class T> constexpr typename remove_reference<T>::type &&move(T &&t) {
+ return static_cast<typename remove_reference<T>::type>(t);
+}
+
+template <class T>
+constexpr T &&forward(typename remove_reference<T>::type &t) {
+ return static_cast<T &&>(t);
+}
+
+template <class T>
+constexpr T &&forward(typename remove_reference<T>::type &&t) {
+ return static_cast<T &&>(t);
+}
+
+template <class T> constexpr const T &as_const(T &x) { return x; }
+
+template <class T, bool RValueRef> struct PickRef {
+ using type = typename remove_reference<T>::type &;
+};
+template <class T> struct PickRef<T, true> {
+ using type = typename remove_reference<T>::type &&;
+};
+
+template <class T>
+auto move_if_noexcept(T &t) ->
+ typename PickRef<T, noexcept(T(static_cast<T &&>(t)))>::type {
+ return static_cast<
+ typename PickRef<T, noexcept(T(static_cast<T &&>(t)))>::type>(t);
+}
+
+template <class T> T *addressof(T &arg) {
+ return reinterpret_cast<T *>(
+ &const_cast<char &>(reinterpret_cast<const volatile char &>(arg)));
+}
+
+} // namespace foo
+} // namespace std
+
+namespace move_forward_et_al_examples {
+ struct S {
+ S &self() [[clang::lifetimebound]] { return *this; }
+ };
+
+ S &&Move = std::move(S{}); // expected-warning {{temporary bound to local reference 'Move' will be destroyed at the end of the full-expression}}
+ S MoveOk = std::move(S{});
+
+ S &&Forward = std::forward<S &&>(S{}); // expected-warning {{temporary bound to local reference 'Forward' will be destroyed at the end of the full-expression}}
+ S ForwardOk = std::forward<S &&>(S{});
+
+ const S &Const = std::as_const(S{}.self()); // expected-warning {{temporary bound to local reference 'Const' will be destroyed at the end of the full-expression}}
+ const S ConstOk = std::as_const(S{}.self());
+
+ S &&MoveIfNoExcept = std::move_if_noexcept(S{}.self()); // expected-warning {{temporary bound to local reference 'MoveIfNoExcept' will be destroyed at the end of the full-expression}}
+ S MoveIfNoExceptOk = std::move_if_noexcept(S{}.self());
+
+ S *AddressOf = std::addressof(S{}.self()); // expected-warning {{temporary whose address is used as value of local variable 'AddressOf' will be destroyed at the end of the full-expression}}
+ S X;
+ S *AddressOfOk = std::addressof(X);
+} // namespace move_forward_et_al_examples
Index: clang/lib/Sema/SemaDecl.cpp
===================================================================
--- clang/lib/Sema/SemaDecl.cpp
+++ clang/lib/Sema/SemaDecl.cpp
@@ -16182,6 +16182,24 @@
default:
break;
}
+
+ // Add lifetime attribute to std::move, std::fowrard et al.
+ switch (BuiltinID) {
+ case Builtin::BIaddressof:
+ case Builtin::BI__addressof:
+ case Builtin::BI__builtin_addressof:
+ case Builtin::BIas_const:
+ case Builtin::BIforward:
+ case Builtin::BImove:
+ case Builtin::BImove_if_noexcept:
+ if (ParmVarDecl *P = FD->getParamDecl(0u);
+ !P->hasAttr<LifetimeBoundAttr>())
+ P->addAttr(
+ LifetimeBoundAttr::CreateImplicit(Context, FD->getLocation()));
+ break;
+ default:
+ break;
+ }
}
AddKnownFunctionAttributesForReplaceableGlobalAllocationFunction(FD);
Index: clang/docs/ReleaseNotes.rst
===================================================================
--- clang/docs/ReleaseNotes.rst
+++ clang/docs/ReleaseNotes.rst
@@ -458,6 +458,9 @@
only when ``x`` is a string literal.
- Clang will now reject the GNU extension address of label in coroutines explicitly.
This fixes `Issue 56436 <https://github.com/llvm/llvm-project/issues/56436>`_.
+- Clang now automatically adds ``[[clang::lifetimebound]]`` to the parameters of
+ ``std::move, std::forward`` et al, this enables Clang to diagnose more cases
+ where the returned reference outlives the object.
Non-comprehensive list of changes in this release
-------------------------------------------------
Index: clang/docs/LanguageExtensions.rst
===================================================================
--- clang/docs/LanguageExtensions.rst
+++ clang/docs/LanguageExtensions.rst
@@ -2933,7 +2933,8 @@
``__builtin_addressof`` performs the functionality of the built-in ``&``
operator, ignoring any ``operator&`` overload. This is useful in constant
expressions in C++11, where there is no other way to take the address of an
-object that overloads ``operator&``.
+object that overloads ``operator&``. Clang automatically adds
+``[[clang::lifetimebound]]`` to the parameter of ``__builtin_addressof``.
**Example of use**:
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