[{"id":3680583,"web_url":"http://patchwork.ozlabs.org/comment/3680583/","msgid":"","list_archive_url":null,"date":"2026-04-22T12:14:23","subject":"Re: [PATCH v2] libstdc++: Mandate power of two alignment for\n std::is_sufficiently_aligned.","submitter":{"id":48004,"url":"http://patchwork.ozlabs.org/api/people/48004/","name":"Jonathan Wakely","email":"jwakely@redhat.com"},"content":"On Wed, 22 Apr 2026 at 12:51, Tomasz Kamiński wrote:\n>\n> This implements LWG4290. Missing Mandates clauses on is_sufficiently_aligned.\n>\n> libstdc++-v3/ChangeLog:\n>\n> * include/bits/align.h (is_sufficiently_aligned): Mandate\n> that _Align is power of two.\n> * testsuite/20_util/is_sufficiently_aligned/2_neg.cc: New test.\n> ---\n> v2 replaces a test file used for chrono::format compilation time\n> testing, with actual test for is_sufficiently_aligned.\n>\n> The test was included in previous run. OK for trunk?\n\nOK\n\n\n>\n> libstdc++-v3/include/bits/align.h | 5 ++++-\n> .../20_util/is_sufficiently_aligned/2_neg.cc | 12 ++++++++++++\n> 2 files changed, 16 insertions(+), 1 deletion(-)\n> create mode 100644 libstdc++-v3/testsuite/20_util/is_sufficiently_aligned/2_neg.cc\n>\n> diff --git a/libstdc++-v3/include/bits/align.h b/libstdc++-v3/include/bits/align.h\n> index 1a14e282216..3c8355d0e07 100644\n> --- a/libstdc++-v3/include/bits/align.h\n> +++ b/libstdc++-v3/include/bits/align.h\n> @@ -116,7 +116,10 @@ align(size_t __align, size_t __size, void*& __ptr, size_t& __space) noexcept\n> [[nodiscard,__gnu__::__always_inline__]]\n> inline bool\n> is_sufficiently_aligned(_Tp* __ptr)\n> - { return reinterpret_cast<__UINTPTR_TYPE__>(__ptr) % _Align == 0; }\n> + {\n> + static_assert(std::has_single_bit(_Align));\n> + return reinterpret_cast<__UINTPTR_TYPE__>(__ptr) % _Align == 0;\n> + }\n> #endif // __glibcxx_is_sufficiently_aligned\n>\n> _GLIBCXX_END_NAMESPACE_VERSION\n> diff --git a/libstdc++-v3/testsuite/20_util/is_sufficiently_aligned/2_neg.cc b/libstdc++-v3/testsuite/20_util/is_sufficiently_aligned/2_neg.cc\n> new file mode 100644\n> index 00000000000..9db69b67ef6\n> --- /dev/null\n> +++ b/libstdc++-v3/testsuite/20_util/is_sufficiently_aligned/2_neg.cc\n> @@ -0,0 +1,12 @@\n> +// { dg-do compile { target c++26 } }\n> +\n> +#include \n> +\n> +void\n> +test01(int* ptr)\n> +{\n> + (void)std::is_sufficiently_aligned<5>(ptr); // { dg-error \"here\" }\n> + (void)std::is_sufficiently_aligned<7>(ptr); // { dg-error \"here\" }\n> +}\n> +\n> +// { dg-error \"static assertion failed\" \"\" { target *-*-* } 0 }\n> --\n> 2.53.0\n>","headers":{"Return-Path":"","X-Original-To":["incoming@patchwork.ozlabs.org","gcc-patches@gcc.gnu.org"],"Delivered-To":["patchwork-incoming@legolas.ozlabs.org","gcc-patches@gcc.gnu.org"],"Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (1024-bit key;\n unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256\n header.s=mimecast20190719 header.b=UEM8geGH;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=gcc.gnu.org\n (client-ip=2620:52:6:3111::32; helo=vm01.sourceware.org;\n envelope-from=gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org;\n receiver=patchwork.ozlabs.org)","sourceware.org;\n\tdkim=pass (1024-bit key,\n unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256\n header.s=mimecast20190719 header.b=UEM8geGH","sourceware.org; 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