From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id 383A0383E82A; Thu, 28 Jan 2021 21:23:54 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 383A0383E82A From: "cvs-commit at gcc dot gnu.org" To: gcc-bugs@gcc.gnu.org Subject: [Bug c++/94775] [8/9/10/11 Regression] ICE in strip_typedefs, at cp/tree.c:1734 since r8-4668-g8a5ee94a082b3d48 Date: Thu, 28 Jan 2021 21:23:53 +0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: c++ X-Bugzilla-Version: 10.0 X-Bugzilla-Keywords: ice-on-valid-code X-Bugzilla-Severity: normal X-Bugzilla-Who: cvs-commit at gcc dot gnu.org X-Bugzilla-Status: ASSIGNED X-Bugzilla-Resolution: X-Bugzilla-Priority: P2 X-Bugzilla-Assigned-To: mpolacek at gcc dot gnu.org X-Bugzilla-Target-Milestone: 8.5 X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: Message-ID: In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/ Auto-Submitted: auto-generated MIME-Version: 1.0 X-BeenThere: gcc-bugs@gcc.gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Gcc-bugs mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 28 Jan 2021 21:23:54 -0000 https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D94775 --- Comment #18 from CVS Commits --- The master branch has been updated by Marek Polacek : https://gcc.gnu.org/g:513ee7d2cd9a60339a50dc9c4cba39a8f1c707f0 commit r11-6963-g513ee7d2cd9a60339a50dc9c4cba39a8f1c707f0 Author: Marek Polacek Date: Thu Jan 28 16:21:50 2021 -0500 tree: Don't reuse types if TYPE_USER_ALIGN differ [PR94775] A year ago I submitted this patch: ~~ Here we trip on the TYPE_USER_ALIGN (t) assert in strip_typedefs: it gets "const d[0]" with TYPE_USER_ALIGN=3D0 but the result built by build_cplus_array_type is "const char[0]" with TYPE_USER_ALIGN=3D1. When we strip_typedefs the element of the array "const d", we see it's a typedef_variant_p, so we look at its DECL_ORIGINAL_TYPE, which is char, but we need to add the const qualifier, so we call cp_build_qualified_type -> build_qualified_type where get_qualified_type checks to see if we already have such a type by walking the variants list, which in this case is: char -> c -> const char -> const char -> d -> const d Because check_base_type only checks TYPE_ALIGN and not TYPE_USER_ALIGN, we choose the first const char, which has TYPE_USER_ALIGN set. If the element type of an array has TYPE_USER_ALIGN, the array type gets it to= o. So we can make check_base_type stricter. I was afraid that it might ma= ke us reuse types less often, but measuring showed that we build the same amount of types with and without the patch, while bootstrapping. ~~ However, the patch broke a few tests on STRICT_ALIGNMENT platforms and had to be reverted. This is another try. The original patch is kept unchanged, but I added the finalize_type_size hunk that ought to fix the STRICT_ALIGNMENT issues. The problem is that finalize_type_size can clear TYPE_USER_ALIGN on the main variant of a type, but doesn't clear it on any of the variants. Then we end up with types which share the same TYPE_MAIN_VARIANT, but their TYPE_CANONICAL differs and then the usual "canonical types differ for identical types" follows. I've created alignas19.C to exercise this scenario. What happens is: - when parsing the class S we create a type S in xref_tag, - we see alignas(8) so common_handle_aligned_attribute sets T_U_A in S, - we parse the member function fn and build_memfn_type creates a copy of S to add const; this variant has T_U_A set, - we finish_struct S which calls layout_class_type -> finish_record_type -> finalize_size_type where we reset T_U_A in S (but const S keeps it= ), - finish_non_static_data_member for arr calls maybe_dummy_object with type =3D S, - maybe_dummy_object calls same_type_ignoring_top_level_qualifiers_p to check if S and TREE_TYPE (current_class_ref), which is const S, are the same, - same_type_ignoring_top_level_qualifiers_p creates cv-unqualified versions of the passed types. Previously we'd use our main variant S when stripping "const S" of const, but since the T_U_A flags don't match (check_base_type), we create a new variant S'. Then we crash in comptypes because S and S' have the same TYPE_MAIN_VARIANT but different TYPE_CANONICALs. With my patch we'll clear T_U_A for S's variants too, and then instead of S' we'll just use S. gcc/ChangeLog: PR c++/94775 * stor-layout.c (finalize_type_size): If we reset TYPE_USER_ALI= GN in the main variant, maybe reset it in its variants too. * tree.c (check_base_type): Return true only if TYPE_USER_ALIGN match. (check_aligned_type): Check if TYPE_USER_ALIGN match. gcc/testsuite/ChangeLog: PR c++/94775 * g++.dg/cpp0x/alignas19.C: New test. * g++.dg/warn/Warray-bounds15.C: New test.=