https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89780
--- Comment #9 from CVS 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:6602a2b2dee16af6e2d451c704789356042b5881 commit r13-2096-g6602a2b2dee16af6e2d451c704789356042b5881 Author: Marek Polacek <pola...@redhat.com> Date: Wed Aug 3 19:47:30 2022 -0400 c++: Tweak for -Wpessimizing-move in templates [PR89780] In my previous patches I've been extending our std::move warnings, but this tweak actually dials it down a little bit. As reported in bug 89780, it's questionable to warn about expressions in templates that were type-dependent, but aren't anymore because we're instantiating the template. As in, template <typename T> Dest withMove() { T x; return std::move(x); } template Dest withMove<Dest>(); // #1 template Dest withMove<Source>(); // #2 Saying that the std::move is pessimizing for #1 is not incorrect, but it's not useful, because removing the std::move would then pessimize #2. So the user can't really win. At the same time, disabling the warning just because we're in a template would be going too far, I still want to warn for template <typename> Dest withMove() { Dest x; return std::move(x); } because the std::move therein will be pessimizing for any instantiation. So I'm using the suppress_warning machinery to that effect. Problem: I had to add a new group to nowarn_spec_t, otherwise suppressing the -Wpessimizing-move warning would disable a whole bunch of other warnings, which we really don't want. PR c++/89780 gcc/cp/ChangeLog: * pt.cc (tsubst_copy_and_build) <case CALL_EXPR>: Maybe suppress -Wpessimizing-move. * typeck.cc (maybe_warn_pessimizing_move): Don't issue warnings if they are suppressed. (check_return_expr): Disable -Wpessimizing-move when returning a dependent expression. gcc/ChangeLog: * diagnostic-spec.cc (nowarn_spec_t::nowarn_spec_t): Handle OPT_Wpessimizing_move and OPT_Wredundant_move. * diagnostic-spec.h (nowarn_spec_t): Add NW_REDUNDANT enumerator. gcc/testsuite/ChangeLog: * g++.dg/cpp0x/Wpessimizing-move3.C: Remove dg-warning. * g++.dg/cpp0x/Wredundant-move2.C: Likewise.
