From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 48) id 7B1743858005; Wed, 19 Jul 2023 09:03:46 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org 7B1743858005 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org; s=default; t=1689757426; bh=LBt+oj7UavaPmZa6UTPX/N+z/UCWuhVTQWM5jPYaylM=; h=From:To:Subject:Date:From; b=ivZqRrnIpVab7Jw7KCPaGLFKp1mRn53/QKCsdDJWnQFIAvCIQmU022N0YrILqIUlc jM1/x8VES4qUs6LPm2DJilp4GqUdTpKCLoDzaEyd0Z5iIA9IDqZZkAeeXtLZgyl87/ UYwF8ee4U0oUiGhs6zKCltDY4QM+i4i/YrQQceIM= From: "shaohua.li at inf dot ethz.ch" To: gcc-bugs@gcc.gnu.org Subject: [Bug c/110738] New: GCC trunk failed to do some optimizations since GCC-8 Date: Wed, 19 Jul 2023 09:03:45 +0000 X-Bugzilla-Reason: CC X-Bugzilla-Type: new X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: gcc X-Bugzilla-Component: c X-Bugzilla-Version: 14.0 X-Bugzilla-Keywords: X-Bugzilla-Severity: normal X-Bugzilla-Who: shaohua.li at inf dot ethz.ch X-Bugzilla-Status: UNCONFIRMED X-Bugzilla-Resolution: X-Bugzilla-Priority: P3 X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org X-Bugzilla-Target-Milestone: --- X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: bug_id short_desc product version bug_status bug_severity priority component assigned_to reporter target_milestone Message-ID: 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=3D110738 Bug ID: 110738 Summary: GCC trunk failed to do some optimizations since GCC-8 Product: gcc Version: 14.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c Assignee: unassigned at gcc dot gnu.org Reporter: shaohua.li at inf dot ethz.ch Target Milestone: --- For the following test case, gcc trunk at -O3 emits a relatively large asse= mbly code since GCC-8. Clang can remove all the code. Compiler explorer: https://godbolt.org/z/hzf8Pr484 The test case is adapted from an official GCC test case: https://github.com/gcc-mirror/gcc/blob/ae862e0e47cb2d62d7c624ab999a3bd8bd29= 14ef/gcc/testsuite/gcc.dg/strncmp-3.c I only changed `int neg=3D0` to `int neg=3D1`.=20 $ gcc-tk -O3 -S -o trunk.s a.c $ gcc-7.4 -O3 -S -o old.s a.c $ wc trunk.s old.s 217 654 5999 trunk.s 11 19 175 old.s 228 673 6174 total $ $ cat a.c #define AB_D "ab\0d" #define ABCDEF_H "abcdef\0h" #define ABCDEFGHIJKLMN_P "abcdefghijklmn\0p" char ab_d[] =3D AB_D; char abcdef_h[] =3D ABCDEF_H; extern int strncmp (const char*, const char*, __SIZE_TYPE__); __attribute__((noipa)) void sink (const void *p, ...) { (void)&p; } #define strncmp(a, b, n) (sink (a, b), strncmp (a, b, n)) int main (void) { int zero =3D 0; zero +=3D strncmp (ab_d, AB_D,1); zero +=3D strncmp (ab_d, AB_D,2); zero +=3D strncmp (ab_d, AB_D,3); zero +=3D strncmp (ab_d, AB_D,4); zero +=3D strncmp (ab_d, AB_D,5); zero +=3D strncmp (ab_d, ABCDEF_H,1); zero +=3D strncmp (ab_d, ABCDEF_H,2); zero +=3D strncmp (abcdef_h, AB_D,2); zero +=3D strncmp (abcdef_h, ABCDEF_H,2); zero +=3D strncmp (abcdef_h, ABCDEF_H,3); zero +=3D strncmp (abcdef_h, ABCDEF_H,4); zero +=3D strncmp (abcdef_h, ABCDEF_H,5); zero +=3D strncmp (abcdef_h, ABCDEF_H,6); zero +=3D strncmp (abcdef_h, ABCDEF_H,7); zero +=3D strncmp (abcdef_h, ABCDEF_H,8); zero +=3D strncmp (abcdef_h, ABCDEF_H,9); if (zero !=3D 0) __builtin_abort (); int neg =3D 1; neg -=3D strncmp (ab_d, ABCDEF_H,3) <0; neg -=3D strncmp (ab_d, ABCDEF_H,4) <0; neg -=3D strncmp (ab_d, ABCDEF_H,5) <0; neg -=3D strncmp (ab_d, ABCDEF_H,6) <0; neg -=3D strncmp (ab_d, ABCDEF_H,7) <0; neg -=3D strncmp (ab_d, ABCDEF_H,8) <0; neg -=3D strncmp (ab_d, ABCDEF_H,9) <0; if (neg !=3D-7){ __builtin_abort (); } } $ $ gcc-tk -v Using built-in specs. COLLECT_GCC=3Dgcc-tk COLLECT_LTO_WRAPPER=3D/zdata/shaoli/compilers/ccbuilder-compilers/gcc-ec842= 611618c9f8a50f3326d42c51961de8b28a5/libexec/gcc/x86_64-pc-linux-gnu/14.0.0/= lto-wrapper Target: x86_64-pc-linux-gnu Configured with: ../configure --disable-multilib --disable-bootstrap --enable-languages=3Dc,c++ --prefix=3D/zdata/shaoli/compilers/ccbuilder-compilers/gcc-ec842611618c9f8a= 50f3326d42c51961de8b28a5 Thread model: posix Supported LTO compression algorithms: zlib gcc version 14.0.0 20230719 (experimental) (GCC)=20 $=