Author: Richard Smith Date: 2022-04-18T11:11:21-07:00 New Revision: e43c93dd63cca295ef26ab69cd305816a71d45fd
URL: https://github.com/llvm/llvm-project/commit/e43c93dd63cca295ef26ab69cd305816a71d45fd DIFF: https://github.com/llvm/llvm-project/commit/e43c93dd63cca295ef26ab69cd305816a71d45fd.diff LOG: Don't treat 'T &forward(T&&)' as builtin. This allows the standard library to diagnose it properly. Suppress warning in libc++ testsuite for unused result of call to std::forward. Added: Modified: clang/lib/Sema/SemaTemplateInstantiateDecl.cpp clang/test/SemaCXX/builtin-std-move.cpp libcxx/test/std/utilities/utility/forward/forward.fail.cpp Removed: ################################################################################ diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp index 8b0147fc66c36..f11a1748e5c68 100644 --- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp +++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp @@ -621,6 +621,20 @@ static bool isRelevantAttr(Sema &S, const Decl *D, const Attr *A) { return true; } + if (const auto *BA = dyn_cast<BuiltinAttr>(A)) { + // Do not treat 'std::forward' as a builtin if it takes an rvalue reference + // type and returns an lvalue reference type. The library implementation + // will produce an error in this case; don't get in its way. + if (BA->getID() == Builtin::BIforward) { + const FunctionDecl *FD = dyn_cast<FunctionDecl>(D); + if (FD && FD->getNumParams() >= 1 && + FD->getParamDecl(0)->getType()->isRValueReferenceType() && + FD->getReturnType()->isLValueReferenceType()) { + return false; + } + } + } + return true; } diff --git a/clang/test/SemaCXX/builtin-std-move.cpp b/clang/test/SemaCXX/builtin-std-move.cpp index a53e57c86c14c..7f1b01e43d788 100644 --- a/clang/test/SemaCXX/builtin-std-move.cpp +++ b/clang/test/SemaCXX/builtin-std-move.cpp @@ -30,11 +30,18 @@ namespace std { template<typename T> struct remove_reference<T&> { using type = T; }; template<typename T> struct remove_reference<T&&> { using type = T; }; + template<typename T> struct is_lvalue_reference { static constexpr bool value = false; }; + template<typename T> struct is_lvalue_reference<T&> { static constexpr bool value = true; }; + template<typename T> CONSTEXPR T &&forward(typename remove_reference<T>::type &x) { static_assert(T::moveable, "instantiated forward"); // expected-error {{no member named 'moveable' in 'B'}} // expected-error@-1 {{no member named 'moveable' in 'C'}} return static_cast<T&&>(x); } + template<typename T> CONSTEXPR T &&forward(typename remove_reference<T>::type &&x) { + static_assert(!is_lvalue_reference<T>::value, "should not forward rval as lval"); // expected-error {{static_assert failed}} + return static_cast<T&&>(x); + } template<typename T> CONSTEXPR const T &as_const(T &x) { static_assert(T::moveable, "instantiated as_const"); // expected-error {{no member named 'moveable' in 'B'}} @@ -76,6 +83,11 @@ static_assert(f({}), "should be constexpr"); // expected-note@#call {{}} #endif +A &forward_rval_as_lval() { + std::forward<A&&>(A()); // expected-warning {{const attribute}} + return std::forward<A&>(A()); // expected-note {{instantiation of}} +} + struct B {}; B &&(*pMove)(B&) = std::move; // #1 expected-note {{instantiation of}} B &&(*pMoveIfNoexcept)(B&) = &std::move_if_noexcept; // #2 expected-note {{instantiation of}} diff --git a/libcxx/test/std/utilities/utility/forward/forward.fail.cpp b/libcxx/test/std/utilities/utility/forward/forward.fail.cpp index 4d7790a751481..f913b835c2248 100644 --- a/libcxx/test/std/utilities/utility/forward/forward.fail.cpp +++ b/libcxx/test/std/utilities/utility/forward/forward.fail.cpp @@ -22,7 +22,7 @@ const A csource() {return A();} int main(int, char**) { { - std::forward<A&>(source()); // expected-note {{requested here}} + (void)std::forward<A&>(source()); // expected-note {{requested here}} // expected-error-re@*:* 1 {{static_assert failed{{.*}} "cannot forward an rvalue as an lvalue"}} } { _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
