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From: "cvs-commit at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug rtl-optimization/106590] [12/13 Regression] x86-64 miscompilation starting with r12-8233-g1ceddd7497e15d w/ mtune=skylake Date: Mon, 15 Aug 2022 11:57:52 +0000 [thread overview] Message-ID: <bug-106590-4-4jMmcUAE3T@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-106590-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106590 --- Comment #8 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jakub Jelinek <jakub@gcc.gnu.org>: https://gcc.gnu.org/g:3a74a7bf62f47ed0d19866576378724be932ee17 commit r13-2042-g3a74a7bf62f47ed0d19866576378724be932ee17 Author: Jakub Jelinek <jakub@redhat.com> Date: Mon Aug 15 13:56:57 2022 +0200 ifcvt: Fix up noce_convert_multiple_sets [PR106590] The following testcase is miscompiled on x86_64-linux. The problem is in the noce_convert_multiple_sets optimization. We essentially have: if (g == 1) { g = 1; f = 23; } else { g = 2; f = 20; } and for each insn try to create a conditional move sequence. There is code to detect overlap with the regs used in the condition and the destinations, so we actually try to construct: tmp_g = g == 1 ? 1 : 2; f = g == 1 ? 23 : 20; g = tmp_g; which is fine. But, we actually try to create two different conditional move sequences in each case, seq1 with the whole (eq (reg/v:HI 82 [ g ]) (const_int 1 [0x1])) condition and seq2 with cc_cmp (eq (reg:CCZ 17 flags) (const_int 0 [0])) to rely on the earlier present comparison. In each case, we compare the rtx costs and choose the cheaper sequence (seq1 if both have the same cost). The problem is that with the skylake tuning, tmp_g = g == 1 ? 1 : 2; is actually expanded as tmp_g = (g == 1) + 1; in seq1 (which clobbers (reg 17 flags)) and as a cmov in seq2 (which doesn't). The tuning says both have the same cost, so we pick seq1. Next we check sequences for f = g == 1 ? 23 : 20; and here the seq2 cmov is cheaper, but it uses (reg 17 flags) which has been clobbered earlier. The following patch fixes that by detecting if we in the chosen sequence clobber some register mentioned in cc_cmp or rev_cc_cmp, and if yes, arranges for only seq1 (i.e. sequences that emit the comparison itself) to be used after that. 2022-08-15 Jakub Jelinek <jakub@redhat.com> PR rtl-optimization/106590 * ifcvt.cc (check_for_cc_cmp_clobbers): New function. (noce_convert_multiple_sets_1): If SEQ sets or clobbers any regs mentioned in cc_cmp or rev_cc_cmp, don't consider seq2 for any further conditional moves. * gcc.dg/torture/pr106590.c: New test.
next prev parent reply other threads:[~2022-08-15 11:57 UTC|newest] Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-08-12 4:23 [Bug target/106590] New: x86-64 miscompilation starting with "i386: Improve ix86_expand_int_movcc" " andres at anarazel dot de 2022-08-12 4:23 ` [Bug target/106590] " andres at anarazel dot de 2022-08-12 4:37 ` [Bug target/106590] [12/13 Regression] " pinskia at gcc dot gnu.org 2022-08-12 4:38 ` pinskia at gcc dot gnu.org 2022-08-12 4:52 ` [Bug rtl-optimization/106590] [12/13 Regression] x86-64 miscompilation starting with r12-8233-g1ceddd7497e15d " pinskia at gcc dot gnu.org 2022-08-12 4:53 ` pinskia at gcc dot gnu.org 2022-08-12 4:59 ` pinskia at gcc dot gnu.org 2022-08-12 6:40 ` rguenth at gcc dot gnu.org 2022-08-12 13:47 ` jakub at gcc dot gnu.org 2022-08-12 14:46 ` jakub at gcc dot gnu.org 2022-08-15 11:57 ` cvs-commit at gcc dot gnu.org [this message] 2022-08-15 12:00 ` jakub at gcc dot gnu.org 2022-08-29 10:05 ` cvs-commit at gcc dot gnu.org 2022-08-30 9:11 ` jakub at gcc dot gnu.org
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