From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id 240AF385800A; Wed, 19 Jul 2023 11:50:11 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 240AF385800A DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org; s=default; t=1689767411; bh=GVSzdVP91v/Ejw3Ny3CwO8H4y3Jfb43/R1WgTfuk6hY=; h=From:To:Subject:Date:In-Reply-To:References:From; b=RSVxSF0QxiOXqYSFlqEx2dFSzGv4XInNMmkOahqes1E9ptKaimtPVrHbzI9eSqT5M jp23FkJsi7Wji86TP2I8dabNLTOmwBMuOo/xAQJfkWjpimd3oTX5poiUETDDABuVnG 6q9RBH5hWd8lUJmiMRRvRXGTCtA/j4NJalN6vL6E= From: "cvs-commit at gcc dot gnu.org" To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/110731] [11/12/13/14 Regression] Wrong-code because of wide-int division since r5-424 Date: Wed, 19 Jul 2023 11:50:10 +0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: tree-optimization X-Bugzilla-Version: 14.0 X-Bugzilla-Keywords: wrong-code X-Bugzilla-Severity: normal X-Bugzilla-Who: cvs-commit at gcc dot gnu.org X-Bugzilla-Status: NEW X-Bugzilla-Resolution: X-Bugzilla-Priority: P2 X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org X-Bugzilla-Target-Milestone: 11.5 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 List-Id: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110731 --- Comment #3 from CVS Commits --- The master branch has been updated by Jakub Jelinek : https://gcc.gnu.org/g:ece799607c841676f4e00c2fea98bbec6976da3f commit r14-2642-gece799607c841676f4e00c2fea98bbec6976da3f Author: Jakub Jelinek Date: Wed Jul 19 13:48:53 2023 +0200 wide-int: Fix up wi::divmod_internal [PR110731] As the following testcase shows, wi::divmod_internal doesn't handle correctly signed division with precision > 64 when the dividend (and li= kely divisor as well) is the type's minimum and the precision isn't divisible by 64. A few lines above what the patch hunk changes is: /* Make the divisor and dividend positive and remember what we did. */ if (sgn =3D=3D SIGNED) { if (wi::neg_p (dividend)) { neg_dividend =3D -dividend; dividend =3D neg_dividend; dividend_neg =3D true; } if (wi::neg_p (divisor)) { neg_divisor =3D -divisor; divisor =3D neg_divisor; divisor_neg =3D true; } } i.e. we negate negative dividend or divisor and remember those. But, after we do that, when unpacking those values into b_dividend and b_divisor we need to always treat the wide_ints as UNSIGNED, because divmod_internal_2 performs an unsigned division only. Now, if precision <=3D 64, we don't reach here at all, earlier code handles it. If dividend or divisor aren't the most negative values, the negation clears their most significant bit, so it doesn't really matter if we unpack SIGNED or UNSIGNED. And if precision is multiple of HOST_BITS_PER_WIDE_INT, there is no difference in behavior, while -0x80000000000000000000000000000000 negates to -0x80000000000000000000000000000000 the unpacking of it as SIGNED or UNSIGNED works the same. In the testcase, we have signed precision 119 and the dividend is val =3D { 0, 0xffc0000000000000 }, len =3D 2, precision =3D 119 both before and after negation. Divisor is val =3D { 2 }, len =3D 1, precision =3D 119 But we really want to divide 0x400000000000000000000000000000 by 2 unsigned and then negate at the end. If it is unsigned precision 119 division 0x400000000000000000000000000000 by 2 dividend is val =3D { 0, 0xffc0000000000000 }, len =3D 2, precision =3D 119 but as we unpack it UNSIGNED, it is unpacked into 0, 0, 0, 0x00400000 The following patch fixes it by always using UNSIGNED unpacking because we've already negated negative values at that point if sgn =3D=3D SIGNED and so most negative constants should be treated as positive. 2023-07-19 Jakub Jelinek PR tree-optimization/110731 * wide-int.cc (wi::divmod_internal): Always unpack dividend and divisor as UNSIGNED regardless of sgn. * gcc.dg/pr110731.c: New test.=