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From: "steven at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug target/56309] -O3 optimizer generates conditional moves instead of compare and branch resulting in almost 2x slower code Date: Thu, 14 Feb 2013 17:10:00 -0000 [thread overview] Message-ID: <bug-56309-4-DUSLWf5IZi@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-56309-4@http.gcc.gnu.org/bugzilla/> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56309 --- Comment #12 from Steven Bosscher <steven at gcc dot gnu.org> 2013-02-14 17:10:02 UTC --- A bit more clear with insn 195 added: 195: flags:CC=cmp(r124:DI,r235:DI) 197: r116:DI={(gtu(flags:CC,0))?r125:DI:r233:DI} 199: {r110:DI=r110:DI+0x1;clobber flags:CC;} 201: flags:CC=cmp(r124:DI,r235:DI) 202: r221:DI={(gtu(flags:CC,0))?r126:DI:r124:DI} insns 195 and 201 compute the same condition but GCC can't eliminate the comparison in insns 201 because insn 199 clobbers the flags (i.e. destroys the result from insn 195). As for speed, of course I can measure that myself: --- by-val-O3.s.orig 2013-02-14 18:06:56.000000000 +0100 +++ by-val-O3.s 2013-02-14 18:07:23.000000000 +0100 @@ -357,9 +357,8 @@ shrq $32, %rdi cmpq %r8, %rdx cmovbe %r11, %rdi - addq $1, %rax - cmpq %r8, %rdx cmovbe %rdx, %rcx + addq $1, %rax cmpq %rbp, %rax movq %rcx, -8(%rsi,%rax,8) jne .L50 unmodified: Took 14.31 seconds total. modified: Took 13.04 seconds total. So re. comment #9: it's not the problem but it'd be a small improvement.
next prev parent reply other threads:[~2013-02-14 17:10 UTC|newest] Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top 2013-02-13 20:21 [Bug middle-end/56309] New: " arturomdn at gmail dot com 2013-02-13 20:23 ` [Bug middle-end/56309] " arturomdn at gmail dot com 2013-02-13 20:26 ` [Bug target/56309] " pinskia at gcc dot gnu.org 2013-02-13 20:29 ` arturomdn at gmail dot com 2013-02-14 8:16 ` ubizjak at gmail dot com 2013-02-14 8:22 ` ubizjak at gmail dot com 2013-02-14 8:28 ` ubizjak at gmail dot com 2013-02-14 14:49 ` ysrumyan at gmail dot com 2013-02-14 15:53 ` arturomdn at gmail dot com 2013-02-14 16:01 ` arturomdn at gmail dot com 2013-02-14 16:44 ` arturomdn at gmail dot com 2013-02-14 16:59 ` steven at gcc dot gnu.org 2013-02-14 17:10 ` steven at gcc dot gnu.org [this message] 2013-02-14 17:26 ` [Bug tree-optimization/56309] " steven at gcc dot gnu.org 2013-02-14 17:31 ` arturomdn at gmail dot com 2013-02-14 17:34 ` ubizjak at gmail dot com 2013-02-14 17:43 ` arturomdn at gmail dot com 2013-02-14 17:50 ` ubizjak at gmail dot com 2013-02-14 18:23 ` ubizjak at gmail dot com 2013-02-14 18:35 ` [Bug target/56309] " ubizjak at gmail dot com 2013-02-14 22:18 ` steven at gcc dot gnu.org 2013-02-15 6:50 ` izamyatin at gmail dot com 2013-02-15 7:15 ` jakub at gcc dot gnu.org 2013-02-15 9:33 ` rguenth at gcc dot gnu.org 2013-02-15 9:36 ` rguenth at gcc dot gnu.org 2013-02-17 8:35 ` [Bug target/56309] conditional moves instead of compare and branch result " ubizjak at gmail dot com 2013-02-17 8:38 ` ubizjak at gmail dot com 2013-02-17 10:10 ` ubizjak at gmail dot com 2013-09-22 6:37 ` icegood1980 at gmail dot com 2013-10-18 9:12 ` jakub at gcc dot gnu.org 2013-10-18 10:06 ` ubizjak at gmail dot com 2015-08-06 9:35 ` ysrumyan at gmail dot com 2021-09-04 20:24 ` peter at cordes dot ca 2021-09-04 20:26 ` peter at cordes dot ca
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