https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113789
--- Comment #8 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The trunk branch has been updated by Marek Polacek <mpola...@gcc.gnu.org>: https://gcc.gnu.org/g:254ff3d0e34835b4de93d5e5763a7366dc7d989d commit r14-9034-g254ff3d0e34835b4de93d5e5763a7366dc7d989d Author: Marek Polacek <pola...@redhat.com> Date: Wed Feb 14 17:53:52 2024 -0500 c++: implicit move with throw [PR113853] Here we have template<class T> auto is_throwable(T t) -> decltype(throw t, true) { ... } where we didn't properly mark 't' as IMPLICIT_RVALUE_P, which caused the wrong overload to have been chosen. Jason figured out it's because we don't correctly implement [expr.prim.id.unqual]#4.2, which post-P2266 says that an id-expression is move-eligible if "the id-expression (possibly parenthesized) is the operand of a throw-expression, and names an implicitly movable entity that belongs to a scope that does not contain the compound-statement of the innermost lambda-expression, try-block, or function-try-block (if any) whose compound-statement or ctor-initializer contains the throw-expression." I worked out that it's trying to say that given struct X { X(); X(const X&); X(X&&) = delete; }; the following should fail: the scope of the throw is an sk_try, and it's also x's scope S, and S "does not contain the compound-statement of the *try-block" so x is move-eligible, so we move, so we fail. void f () try { X x; throw x; // use of deleted function } catch (...) { } Whereas here: void g (X x) try { throw x; } catch (...) { } the throw is again in an sk_try, but x's scope is an sk_function_parms which *does* contain the {} of the *try-block, so x is not move-eligible, so we don't move, so we use X(const X&), and the code is fine. The current code also doesn't seem to handle void h (X x) { void z (decltype(throw x, true)); } where there's no enclosing lambda or sk_try so we should move. I'm not doing anything about lambdas because we shouldn't reach the code at the end of the function: the DECL_HAS_VALUE_EXPR_P check shouldn't let us go further. PR c++/113789 PR c++/113853 gcc/cp/ChangeLog: * typeck.cc (treat_lvalue_as_rvalue_p): Update code to better reflect [expr.prim.id.unqual]#4.2. gcc/testsuite/ChangeLog: * g++.dg/cpp0x/sfinae69.C: Remove dg-bogus. * g++.dg/cpp0x/sfinae70.C: New test. * g++.dg/cpp0x/sfinae71.C: New test. * g++.dg/cpp0x/sfinae72.C: New test. * g++.dg/cpp2a/implicit-move4.C: New test.
