[{"id":3679785,"web_url":"http://patchwork.ozlabs.org/comment/3679785/","msgid":"","list_archive_url":null,"date":"2026-04-21T09:57:27","subject":"Re: [PATCH] libstdc++: Implement P4012R1 while reverting P3844R2\n (consteval simd broadcast)","submitter":{"id":4329,"url":"http://patchwork.ozlabs.org/api/people/4329/","name":"Jonathan Wakely","email":"jwakely.gcc@gmail.com"},"content":"On Mon, 20 Apr 2026 at 16:52, Matthias Kretz wrote:\n>\n> Tested on x86_64-linux-gnu (unix/-march=native and unix/-m32/-march=i686).\n>\n> OK for trunk?\n\nOK, thanks\n\n\n>\n> -------- 8< ---------\n>\n> From: Matthias Kretz \n>\n> P3844R2 added consteval conversion for value-preserving conversion from\n> constants. It had been approved by LEWG in Kona. Therefore, the current\n> implementation has the consteval broadcast constructor. In Croydon, LEWG\n> reversed the decision but changed the overload set to keep the design\n> space open for C++29.\n>\n> This patch implements the removal of the consteval constructor and\n> changes the broadcast constructor according to P4012R1, to keep the\n> design space open.\n>\n> libstdc++-v3/ChangeLog:\n>\n> * include/bits/simd_details.h (__value_preserving_cast): Remove.\n> * include/bits/simd_mask.h (basic_mask): Replace plain 0 and 1\n> literals with cw<0> and cw<1>. Replace explicit basic_vec\n> construction from 0 and 1 with default init and broadcast from\n> _Up(1).\n> (_M_to_uint): Replace 1 with cw<1>.\n> * include/bits/simd_vec.h (basic_vec): Remove consteval\n> broadcast overload. Remove explicit broadcast from\n> non-value-preserving types.\n> * testsuite/std/simd/arithmetic.cc: Replace ill-formed integer\n> literals with explicit cast to T or use cw.\n> * testsuite/std/simd/mask.cc: Likewise.\n> * testsuite/std/simd/simd_alg.cc: Likewise.\n> * testsuite/std/simd/traits_common.cc: Adjust for resulting\n> traits changes.\n> * testsuite/std/simd/traits_math.cc: Likewise.\n>\n> Signed-off-by: Matthias Kretz \n> ---\n> libstdc++-v3/include/bits/simd_details.h | 9 --------\n> libstdc++-v3/include/bits/simd_mask.h | 17 +++++++-------\n> libstdc++-v3/include/bits/simd_vec.h | 22 ++++---------------\n> libstdc++-v3/testsuite/std/simd/arithmetic.cc | 17 +++++++-------\n> libstdc++-v3/testsuite/std/simd/mask.cc | 6 ++---\n> libstdc++-v3/testsuite/std/simd/simd_alg.cc | 5 ++---\n> .../testsuite/std/simd/traits_common.cc | 4 ++--\n> .../testsuite/std/simd/traits_math.cc | 2 +-\n> 8 files changed, 30 insertions(+), 52 deletions(-)\n>\n>\n> --\n> ──────────────────────────────────────────────────────────────────────────\n> Dr. Matthias Kretz https://mattkretz.github.io\n> GSI Helmholtz Center for Heavy Ion Research https://gsi.de\n> std::simd\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 (2048-bit key;\n unprotected) header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256\n header.s=20251104 header.b=EgjE20aw;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=gcc.gnu.org\n (client-ip=38.145.34.32; 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Tue, 21 Apr 2026\n 02:57:39 -0700 (PDT)","MIME-Version":"1.0","References":"<15809688.uLZWGnKmhe@vir-laptop>","In-Reply-To":"<15809688.uLZWGnKmhe@vir-laptop>","From":"Jonathan Wakely ","Date":"Tue, 21 Apr 2026 10:57:27 +0100","X-Gm-Features":"AQROBzCv-T4iy2qrXdtIuj3_v7dHaPT66Kz4PKE31TeQf7-kn-ZK6OfkHjCzFow","Message-ID":"\n ","Subject":"Re: [PATCH] libstdc++: Implement P4012R1 while reverting P3844R2\n (consteval simd broadcast)","To":"Matthias Kretz ","Cc":"libstdc++@gcc.gnu.org, gcc-patches@gcc.gnu.org","Content-Type":"text/plain; charset=\"UTF-8\"","Content-Transfer-Encoding":"quoted-printable","X-BeenThere":"gcc-patches@gcc.gnu.org","X-Mailman-Version":"2.1.30","Precedence":"list","List-Id":"Gcc-patches mailing list ","List-Unsubscribe":",\n ","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n ","Errors-To":"gcc-patches-bounces~incoming=patchwork.ozlabs.org@gcc.gnu.org"}},{"id":3679855,"web_url":"http://patchwork.ozlabs.org/comment/3679855/","msgid":"<14238149.nUPlyArG6x@vir-laptop>","list_archive_url":null,"date":"2026-04-21T12:33:50","subject":"Re: [PATCH] libstdc++: Implement P4012R1 while reverting P3844R2\n (consteval simd broadcast)","submitter":{"id":73288,"url":"http://patchwork.ozlabs.org/api/people/73288/","name":"Matthias Kretz","email":"m.kretz@gsi.de"},"content":"Jonathan Wakely [Tuesday, 21 April 2026, 11:57:27 CEST]:\n> On Mon, 20 Apr 2026 at 16:52, Matthias Kretz wrote:\n> \n> \n> > Tested on x86_64-linux-gnu (unix/-march=native and unix/-m32/-march=i686).\n> > \n> > OK for trunk?\n> \n> OK, thanks\n\nSorry, my v2 patch for this issue got stuck in my outbox. The additional \nchanges in the v2 patch are (they are needed for -ffast-math tests and even \nthen it still doesn't compile because of missing 'fabs'):\n\nin arithmetic.cc:\n\n@@ -259,10 +260,10 @@ struct Tests\n ADD_TEST(divide0, std::is_floating_point_v && !is_iec559) {\n std::tuple{T(2), init_vec},\n [](auto& t, V x, V y) {\n-\tt.verify_equal_to_ulp(x / x, V(T(1)), 1);\n-\tt.verify_equal_to_ulp(T(3) / x, V(T(3) / T(2)), 1);\n-\tt.verify_equal_to_ulp(x / T(3), V(T(2) / T(3)), 1);\n-\tt.verify_equal_to_ulp(y / x, init_vec, \n1);\n+\tt.verify_equal_to_ulp(x / x, V(T(1)), std::cw<1>);\n+\tt.verify_equal_to_ulp(T(3) / x, V(T(3) / T(2)), std::cw<1>);\n+\tt.verify_equal_to_ulp(x / T(3), V(T(2) / T(3)), std::cw<1>);\n+\tt.verify_equal_to_ulp(y / x, init_vec, \nstd::cw<1>);\n }\n };\n \n@@ -272,18 +273,18 @@ struct Tests\n [](auto& t, V a) {\n \tV b = std::cw<2>;\n \tV ref([&](int i) { return a[i] / 2; });\n-\tt.verify_equal_to_ulp(a / b, ref, 1);\n+\tt.verify_equal_to_ulp(a / b, ref, std::cw<1>);\n \ta = select(a == std::cw<0>, T(1), a);\n \t// -freciprocal-math together with flush-to-zero makes\n \t// the following range restriction necessary (i.e.\n \t// 1/|a| must be >= min). Intel vrcpps and vrcp14ps\n \t// need some extra slack (use 1.1 instead of 1).\n \ta = select(fabs(a) >= T(1.1) / norm_min, T(1), a);\n-\tt.verify_equal_to_ulp(a / a, V(1), 1)(\"\\na = \", a);\n+\tt.verify_equal_to_ulp(a / a, V(std::cw<1>), std::cw<1>)(\"\\na = \", a);\n \tref = V([&](int i) { return 2 / a[i]; });\n-\tt.verify_equal_to_ulp(b / a, ref, 1)(\"\\na = \", a);\n-\tt.verify_equal_to_ulp(b /= a, ref, 1);\n-\tt.verify_equal_to_ulp(b, ref, 1);\n+\tt.verify_equal_to_ulp(b / a, ref, std::cw<1>)(\"\\na = \", a);\n+\tt.verify_equal_to_ulp(b /= a, ref, std::cw<1>);\n+\tt.verify_equal_to_ulp(b, ref, std::cw<1>);\n }\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 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 dmarc=pass (p=none dis=none) header.from=gsi.de","sourceware.org; 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The additional\n> changes in the v2 patch are (they are needed for -ffast-math tests and even\n> then it still doesn't compile because of missing 'fabs'):\n\nStill OK for trunk then.\n\n>\n> in arithmetic.cc:\n>\n> @@ -259,10 +260,10 @@ struct Tests\n> ADD_TEST(divide0, std::is_floating_point_v && !is_iec559) {\n> std::tuple{T(2), init_vec},\n> [](auto& t, V x, V y) {\n> - t.verify_equal_to_ulp(x / x, V(T(1)), 1);\n> - t.verify_equal_to_ulp(T(3) / x, V(T(3) / T(2)), 1);\n> - t.verify_equal_to_ulp(x / T(3), V(T(2) / T(3)), 1);\n> - t.verify_equal_to_ulp(y / x, init_vec,\n> 1);\n> + t.verify_equal_to_ulp(x / x, V(T(1)), std::cw<1>);\n> + t.verify_equal_to_ulp(T(3) / x, V(T(3) / T(2)), std::cw<1>);\n> + t.verify_equal_to_ulp(x / T(3), V(T(2) / T(3)), std::cw<1>);\n> + t.verify_equal_to_ulp(y / x, init_vec,\n> std::cw<1>);\n> }\n> };\n>\n> @@ -272,18 +273,18 @@ struct Tests\n> [](auto& t, V a) {\n> V b = std::cw<2>;\n> V ref([&](int i) { return a[i] / 2; });\n> - t.verify_equal_to_ulp(a / b, ref, 1);\n> + t.verify_equal_to_ulp(a / b, ref, std::cw<1>);\n> a = select(a == std::cw<0>, T(1), a);\n> // -freciprocal-math together with flush-to-zero makes\n> // the following range restriction necessary (i.e.\n> // 1/|a| must be >= min). Intel vrcpps and vrcp14ps\n> // need some extra slack (use 1.1 instead of 1).\n> a = select(fabs(a) >= T(1.1) / norm_min, T(1), a);\n> - t.verify_equal_to_ulp(a / a, V(1), 1)(\"\\na = \", a);\n> + t.verify_equal_to_ulp(a / a, V(std::cw<1>), std::cw<1>)(\"\\na = \", a);\n> ref = V([&](int i) { return 2 / a[i]; });\n> - t.verify_equal_to_ulp(b / a, ref, 1)(\"\\na = \", a);\n> - t.verify_equal_to_ulp(b /= a, ref, 1);\n> - t.verify_equal_to_ulp(b, ref, 1);\n> + t.verify_equal_to_ulp(b / a, ref, std::cw<1>)(\"\\na = \", a);\n> + t.verify_equal_to_ulp(b /= a, ref, std::cw<1>);\n> + t.verify_equal_to_ulp(b, ref, std::cw<1>);\n> }\n> };\n>\n> --\n> ──────────────────────────────────────────────────────────────────────────\n> Dr. Matthias Kretz https://mattkretz.github.io\n> GSI Helmholtz Center for Heavy Ion Research https://gsi.de\n> std::simd\n> ──────────────────────────────────────────────────────────────────────────\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=Lx/OKJgz;\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; 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