From patchwork Sat Aug 6 18:13:13 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Marek Polacek X-Patchwork-Id: 56578 Return-Path: X-Original-To: patchwork@sourceware.org Delivered-To: patchwork@sourceware.org Received: from server2.sourceware.org (localhost [IPv6:::1]) by sourceware.org (Postfix) with ESMTP id 9928E385842B for ; Sat, 6 Aug 2022 18:13:50 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 9928E385842B DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org; s=default; t=1659809630; bh=z3BJnGfmPFWT6WgXsJIWxc24tsKqsRSTY2ZM4MmLpHo=; h=To:Subject:Date:List-Id:List-Unsubscribe:List-Archive:List-Post: List-Help:List-Subscribe:From:Reply-To:From; b=ZszRLDJw8BqxS3SNAqx0j2ZTQZsItpRmSc8S8aTNSZIylR6L1PY8LcvOv7euTLW9y 3tzToQMO9g0JJxwvNLe1LdYcoutfCfVl1yHY/vx+mJZoEIU29iexWrbaeWHew9mJ+L 0itoo/z55YvhZ11l+gaXFyP5HR3hG+J/kQgHd66E= X-Original-To: gcc-patches@gcc.gnu.org Delivered-To: gcc-patches@gcc.gnu.org Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by sourceware.org (Postfix) with ESMTPS id 424553858D28 for ; Sat, 6 Aug 2022 18:13:20 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 424553858D28 Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-66-BaQYdP61MRSDPIRx0uJ7wA-1; Sat, 06 Aug 2022 14:13:18 -0400 X-MC-Unique: BaQYdP61MRSDPIRx0uJ7wA-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.rdu2.redhat.com [10.11.54.1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 3A73F101A586 for ; Sat, 6 Aug 2022 18:13:18 +0000 (UTC) Received: from pdp-11.redhat.com (unknown [10.22.8.16]) by smtp.corp.redhat.com (Postfix) with ESMTP id 164AC400E88D; Sat, 6 Aug 2022 18:13:18 +0000 (UTC) To: GCC Patches , Jason Merrill Subject: [PATCH] c++: Extend -Wredundant-move for const-qual objects [PR90428] Date: Sat, 6 Aug 2022 14:13:13 -0400 Message-Id: <20220806181313.337246-1-polacek@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.11.54.1 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com X-Spam-Status: No, score=-12.5 required=5.0 tests=BAYES_00, DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, GIT_PATCH_0, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_NONE, TXREP, T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org X-BeenThere: gcc-patches@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-Patchwork-Original-From: Marek Polacek via Gcc-patches From: Marek Polacek Reply-To: Marek Polacek Errors-To: gcc-patches-bounces+patchwork=sourceware.org@gcc.gnu.org Sender: "Gcc-patches" In this PR, Jon suggested extending the -Wredundant-move warning to warn when the user is moving a const object as in: struct T { }; T f(const T& t) { return std::move(t); } where the std::move is redundant, because T does not have a T(const T&&) constructor (which is very unlikely). Even with the std::move, T(T&&) would not be used because it would mean losing the const. Instead, T(const T&) will be called. I had to restructure the function a bit, but it's better now. This patch depends on my other recent patches to maybe_warn_pessimizing_move. Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk? PR c++/90428 gcc/cp/ChangeLog: * typeck.cc (maybe_warn_pessimizing_move): Extend the -Wredundant-move warning to warn about std::move on a const-qualified object. gcc/testsuite/ChangeLog: * g++.dg/cpp0x/Wredundant-move1.C: Adjust dg-warning. * g++.dg/cpp0x/Wredundant-move9.C: Likewise. * g++.dg/cpp0x/Wredundant-move10.C: New test. --- gcc/cp/typeck.cc | 157 +++++++++++------- gcc/testsuite/g++.dg/cpp0x/Wredundant-move1.C | 3 +- .../g++.dg/cpp0x/Wredundant-move10.C | 61 +++++++ gcc/testsuite/g++.dg/cpp0x/Wredundant-move9.C | 3 +- 4 files changed, 162 insertions(+), 62 deletions(-) create mode 100644 gcc/testsuite/g++.dg/cpp0x/Wredundant-move10.C base-commit: 36e96748edef21eecfe8ffc51dba8ec06e8533ec prerequisite-patch-id: f4862bc588ce5fed1d21016fecc4b61feb71eba5 prerequisite-patch-id: ce490c3c0b991fa7f27315387949c145c66223a4 prerequisite-patch-id: bf551f0fe75fa8f6775fe53469b61ae94d8cab81 diff --git a/gcc/cp/typeck.cc b/gcc/cp/typeck.cc index 70a5efc45de..802bc9c43fb 100644 --- a/gcc/cp/typeck.cc +++ b/gcc/cp/typeck.cc @@ -10411,72 +10411,109 @@ maybe_warn_pessimizing_move (tree expr, tree type, bool return_p) return; } - /* We're looking for *std::move ((T &) &arg). */ - if (REFERENCE_REF_P (expr) - && TREE_CODE (TREE_OPERAND (expr, 0)) == CALL_EXPR) - { - tree fn = TREE_OPERAND (expr, 0); - if (is_std_move_p (fn)) - { - tree arg = CALL_EXPR_ARG (fn, 0); - tree moved; - if (TREE_CODE (arg) != NOP_EXPR) - return; - arg = TREE_OPERAND (arg, 0); - if (TREE_CODE (arg) != ADDR_EXPR) - return; - arg = TREE_OPERAND (arg, 0); - arg = convert_from_reference (arg); - if (can_do_rvo_p (arg, type)) - { - auto_diagnostic_group d; - if (!warning_suppressed_p (expr, OPT_Wpessimizing_move) - && warning_at (loc, OPT_Wpessimizing_move, - "moving a temporary object prevents copy " - "elision")) - inform (loc, "remove % call"); - } - /* The rest of the warnings is only relevant for when we are - returning from a function. */ - else if (!return_p) - return; - /* Warn if we could do copy elision were it not for the move. */ - else if (can_do_nrvo_p (arg, type)) + /* First, check if this is a call to std::move. */ + if (!REFERENCE_REF_P (expr) + || TREE_CODE (TREE_OPERAND (expr, 0)) != CALL_EXPR) + return; + tree fn = TREE_OPERAND (expr, 0); + if (!is_std_move_p (fn)) + return; + tree arg = CALL_EXPR_ARG (fn, 0); + if (TREE_CODE (arg) != NOP_EXPR) + return; + /* If we're looking at *std::move ((T &) &arg), do the pessimizing N/RVO + and implicitly-movable warnings. */ + if (TREE_CODE (TREE_OPERAND (arg, 0)) == ADDR_EXPR) + { + arg = TREE_OPERAND (arg, 0); + arg = TREE_OPERAND (arg, 0); + arg = convert_from_reference (arg); + if (can_do_rvo_p (arg, type)) + { + auto_diagnostic_group d; + if (!warning_suppressed_p (expr, OPT_Wpessimizing_move) + && warning_at (loc, OPT_Wpessimizing_move, + "moving a temporary object prevents copy elision")) + inform (loc, "remove % call"); + } + /* The rest of the warnings is only relevant for when we are returning + from a function. */ + if (!return_p) + return; + + tree moved; + /* Warn if we could do copy elision were it not for the move. */ + if (can_do_nrvo_p (arg, type)) + { + auto_diagnostic_group d; + if (!warning_suppressed_p (expr, OPT_Wpessimizing_move) + && warning_at (loc, OPT_Wpessimizing_move, + "moving a local object in a return statement " + "prevents copy elision")) + inform (loc, "remove % call"); + } + /* Warn if the move is redundant. It is redundant when we would + do maybe-rvalue overload resolution even without std::move. */ + else if (warn_redundant_move + && !warning_suppressed_p (expr, OPT_Wredundant_move) + && (moved = treat_lvalue_as_rvalue_p (arg, /*return*/true))) + { + /* Make sure that overload resolution would actually succeed + if we removed the std::move call. */ + tree t = convert_for_initialization (NULL_TREE, type, + moved, + (LOOKUP_NORMAL + | LOOKUP_ONLYCONVERTING + | LOOKUP_PREFER_RVALUE), + ICR_RETURN, NULL_TREE, 0, + tf_none); + /* If this worked, implicit rvalue would work, so the call to + std::move is redundant. */ + if (t != error_mark_node + /* Trying to move something const will never succeed unless + there's T(const T&&), which it almost never is, and if + so, T wouldn't be error_mark_node now. So do warn. */ + || (CP_TYPE_CONST_P (TREE_TYPE (arg)) + && same_type_ignoring_top_level_qualifiers_p + (TREE_TYPE (arg), type))) { auto_diagnostic_group d; - if (!warning_suppressed_p (expr, OPT_Wpessimizing_move) - && warning_at (loc, OPT_Wpessimizing_move, - "moving a local object in a return statement " - "prevents copy elision")) + if (warning_at (loc, OPT_Wredundant_move, + "redundant move in return statement")) inform (loc, "remove % call"); } - /* Warn if the move is redundant. It is redundant when we would - do maybe-rvalue overload resolution even without std::move. */ - else if (warn_redundant_move - && !warning_suppressed_p (expr, OPT_Wredundant_move) - && (moved = treat_lvalue_as_rvalue_p (arg, /*return*/true))) - { - /* Make sure that overload resolution would actually succeed - if we removed the std::move call. */ - tree t = convert_for_initialization (NULL_TREE, type, - moved, - (LOOKUP_NORMAL - | LOOKUP_ONLYCONVERTING - | LOOKUP_PREFER_RVALUE), - ICR_RETURN, NULL_TREE, 0, - tf_none); - /* If this worked, implicit rvalue would work, so the call to - std::move is redundant. */ - if (t != error_mark_node) - { - auto_diagnostic_group d; - if (warning_at (loc, OPT_Wredundant_move, - "redundant move in return statement")) - inform (loc, "remove % call"); - } - } } } + /* Also try to warn about redundant std::move in code such as + T f (const T& t) + { + return std::move(t); + } + for which EXPR will be something like + *std::move ((const struct T &) (const struct T *) t) + 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 (TREE_CODE (TREE_TYPE (arg)) == REFERENCE_TYPE + && CP_TYPE_CONST_P (TREE_TYPE (TREE_TYPE (arg)))) + { + tree rtype = TREE_TYPE (TREE_TYPE (arg)); + if (!same_type_ignoring_top_level_qualifiers_p (rtype, type)) + return; + /* Check for the unlikely case there's T(const T&&) (we don't care if + it's deleted). */ + for (tree fn : ovl_range (CLASSTYPE_CONSTRUCTORS (rtype))) + if (move_fn_p (fn)) + { + tree t = TREE_VALUE (FUNCTION_FIRST_USER_PARMTYPE (fn)); + if (UNLIKELY (CP_TYPE_CONST_P (TREE_TYPE (t)))) + return; + } + auto_diagnostic_group d; + if (warning_at (loc, OPT_Wredundant_move, + "redundant move in return statement")) + inform (loc, "remove % call"); + } } /* Check that returning RETVAL from the current function is valid. diff --git a/gcc/testsuite/g++.dg/cpp0x/Wredundant-move1.C b/gcc/testsuite/g++.dg/cpp0x/Wredundant-move1.C index ce4087b476f..c227019cce1 100644 --- a/gcc/testsuite/g++.dg/cpp0x/Wredundant-move1.C +++ b/gcc/testsuite/g++.dg/cpp0x/Wredundant-move1.C @@ -60,7 +60,8 @@ fn4 (const T t) { // t is const: will decay into copy despite std::move, so it's redundant. // We used to warn about this, but no longer since c++/87378. - return std::move (t); // { dg-warning "redundant move" "" { target c++20 } } + // Now we warn again since c++/90428. + return std::move (t); // { dg-warning "redundant move" } } int diff --git a/gcc/testsuite/g++.dg/cpp0x/Wredundant-move10.C b/gcc/testsuite/g++.dg/cpp0x/Wredundant-move10.C new file mode 100644 index 00000000000..a215a4774d6 --- /dev/null +++ b/gcc/testsuite/g++.dg/cpp0x/Wredundant-move10.C @@ -0,0 +1,61 @@ +// PR c++/90428 +// { 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); } +} + +struct T { T(); T(const T&); T(T&&) = delete; }; +struct S : T { }; +struct W { W(const W&); W(W&&) = delete; W(const W&&); }; + +T f1(T t) +{ + const T& rt = t; + return std::move(rt); // { dg-warning "redundant move" } +} + +T f2(const T& t) +{ + return std::move(t); // { dg-warning "redundant move" } +} + +W f3(const W& w) +{ + return std::move(w); +} + +T f4(const S& s) +{ + return std::move(s); +} + +T f5(const T t) +{ + return std::move(t); // { dg-warning "redundant move" } +} + +struct S1 { S1(S1 &&) = delete; S1(const S1&); }; +struct S2: S1 {}; + +S1 f3(const S2 s) +{ + return std::move(s); // { dg-warning "redundant move" "" { target c++20 } } +} diff --git a/gcc/testsuite/g++.dg/cpp0x/Wredundant-move9.C b/gcc/testsuite/g++.dg/cpp0x/Wredundant-move9.C index ca1e23b7a4b..489ecd2b9c9 100644 --- a/gcc/testsuite/g++.dg/cpp0x/Wredundant-move9.C +++ b/gcc/testsuite/g++.dg/cpp0x/Wredundant-move9.C @@ -61,7 +61,8 @@ fn4 (const T t) { // t is const: will decay into copy despite std::move, so it's redundant. // We used to warn about this, but no longer since c++/87378. - return std::move (t); // { dg-warning "redundant move" "" { target c++20 } } + // Now we warn again since c++/90428. + return std::move (t); // { dg-warning "redundant move" } } int