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[24.43.233.8]) by smtp.gmail.com with ESMTPSA id cq10-20020a05622a424a00b00397e97baa96sm7034638qtb.0.2022.11.07.14.59.14 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 07 Nov 2022 14:59:14 -0800 (PST) Message-ID: <491a628b-9113-fdf4-bb43-1c6356e3043b@redhat.com> Date: Mon, 7 Nov 2022 12:59:12 -1000 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.4.2 Subject: Re: [PATCH] c++: Tweaks for -Wredundant-move [PR107363] To: Marek Polacek , GCC Patches References: <20221028204233.409310-1-polacek@redhat.com> From: Jason Merrill In-Reply-To: <20221028204233.409310-1-polacek@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-12.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,GIT_PATCH_0,NICE_REPLY_A,RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H2,SPF_HELO_NONE,SPF_NONE,TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: On 10/28/22 10:42, Marek Polacek wrote: > Two things here: > > 1) when we're pointing out that std::move on a constant object is > redundant, don't say "in return statement" when we aren't in a > return statement; > 2) suppress the warning when the std::move call was dependent, because > removing the std::move may not be correct for a different > instantiation of the original template. > > Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk? OK. I'd probably do #2 with a warning_sentinel in tsubst_copy_and_build/CALL_EXPR, but this way makes sense, too. > PR c++/107363 > > gcc/cp/ChangeLog: > > * semantics.cc (finish_call_expr): Suppress OPT_Wpessimizing_move. > * typeck.cc (maybe_warn_pessimizing_move): Check warn_redundant_move > and warning_suppressed_p. Adjust a message depending on return_p. > (check_return_expr): Don't suppress OPT_Wpessimizing_move here. > > gcc/testsuite/ChangeLog: > > * g++.dg/cpp0x/Wredundant-move13.C: New test. > --- > gcc/cp/semantics.cc | 4 ++ > gcc/cp/typeck.cc | 16 ++--- > .../g++.dg/cpp0x/Wredundant-move13.C | 61 +++++++++++++++++++ > 3 files changed, 73 insertions(+), 8 deletions(-) > create mode 100644 gcc/testsuite/g++.dg/cpp0x/Wredundant-move13.C > > diff --git a/gcc/cp/semantics.cc b/gcc/cp/semantics.cc > index 36aa9c4499f..caaa40fde19 100644 > --- a/gcc/cp/semantics.cc > +++ b/gcc/cp/semantics.cc > @@ -2738,6 +2738,10 @@ finish_call_expr (tree fn, vec **args, bool disallow_virtual, > result = build_min_nt_call_vec (orig_fn, *args); > SET_EXPR_LOCATION (result, cp_expr_loc_or_input_loc (fn)); > KOENIG_LOOKUP_P (result) = koenig_p; > + /* Disable the std::move warnings since this call was dependent > + (c++/89780, c++/107363). This also suppresses the > + -Wredundant-move warning. */ > + suppress_warning (result, OPT_Wpessimizing_move); > if (is_overloaded_fn (fn)) > fn = get_fns (fn); > > diff --git a/gcc/cp/typeck.cc b/gcc/cp/typeck.cc > index 2e0fd8fbf17..5f5fb2a212b 100644 > --- a/gcc/cp/typeck.cc > +++ b/gcc/cp/typeck.cc > @@ -10885,7 +10885,9 @@ maybe_warn_pessimizing_move (tree expr, tree type, bool return_p) > and where the std::move does nothing if T does not have a T(const T&&) > constructor, because the argument is const. It will not use T(T&&) > because that would mean losing the const. */ > - else if (TYPE_REF_P (TREE_TYPE (arg)) > + else if (warn_redundant_move > + && !warning_suppressed_p (expr, OPT_Wredundant_move) > + && TYPE_REF_P (TREE_TYPE (arg)) > && CP_TYPE_CONST_P (TREE_TYPE (TREE_TYPE (arg)))) > { > tree rtype = TREE_TYPE (TREE_TYPE (arg)); > @@ -10901,8 +10903,11 @@ maybe_warn_pessimizing_move (tree expr, tree type, bool return_p) > return; > } > auto_diagnostic_group d; > - if (warning_at (loc, OPT_Wredundant_move, > - "redundant move in return statement")) > + if (return_p > + ? warning_at (loc, OPT_Wredundant_move, > + "redundant move in return statement") > + : warning_at (loc, OPT_Wredundant_move, > + "redundant move in initialization")) > inform (loc, "remove % call"); > } > } > @@ -11126,11 +11131,6 @@ check_return_expr (tree retval, bool *no_warning) > /* We don't know if this is an lvalue or rvalue use, but > either way we can mark it as read. */ > mark_exp_read (retval); > - /* Disable our std::move warnings when we're returning > - a dependent expression (c++/89780). */ > - if (retval && TREE_CODE (retval) == CALL_EXPR) > - /* This also suppresses -Wredundant-move. */ > - suppress_warning (retval, OPT_Wpessimizing_move); > return retval; > } > > diff --git a/gcc/testsuite/g++.dg/cpp0x/Wredundant-move13.C b/gcc/testsuite/g++.dg/cpp0x/Wredundant-move13.C > new file mode 100644 > index 00000000000..80e7d80cd02 > --- /dev/null > +++ b/gcc/testsuite/g++.dg/cpp0x/Wredundant-move13.C > @@ -0,0 +1,61 @@ > +// PR c++/107363 > +// { dg-do compile { target c++11 } } > +// { dg-options "-Wredundant-move" } > + > +// Define std::move. > +namespace std { > + template > + struct remove_reference > + { typedef _Tp type; }; > + > + template > + struct remove_reference<_Tp&> > + { typedef _Tp type; }; > + > + template > + struct remove_reference<_Tp&&> > + { typedef _Tp type; }; > + > + template > + constexpr typename std::remove_reference<_Tp>::type&& > + move(_Tp&& __t) noexcept > + { return static_cast::type&&>(__t); } > +} > + > +template > +struct Optional { > + U &value(); > + T release_value() { > + T t = std::move (value ()); > + return t; > + } > +}; > + > +struct Foo {}; > +void test(Optional o) { o.release_value(); } > + > +struct F { > + F(const F&); > + F(F&&) = delete; > +}; > + > +struct Z { > + Z(const Z&) = delete; > + Z(Z&&) = delete; > + Z(const Z&&); > +}; > + > +const F& constfref(); > +const Z& constzref(); > + > +void > +g () > +{ > + // Will call F::F(const F&) w/ and w/o std::move. So it's redundant. > + F f = std::move (constfref()); // { dg-warning "redundant move in initialization" } > + (void) f; > + // Will call Z::Z(const Z&&) w/ std::move, and Z::Z(const Z&) w/o. > + // So it's not redundant. > + Z z = std::move (constzref()); > + (void) z; > +} > > base-commit: e583c86f49b9ef6991b25308a0ad60de9697f24a