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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug middle-end/106892] [11/12/13 Regression] Wrong code at -O3 on x86_64-linux-gnu since r11-963-g80d6f89e78fc3b77 Date: Fri, 09 Sep 2022 09:31:11 +0000 [thread overview] Message-ID: <bug-106892-4-PyVBwEOpsR@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-106892-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106892 --- Comment #9 from Richard Biener <rguenth at gcc dot gnu.org> --- So the reason is that we have # RANGE [-2147483643, 2] _137 = 4 - prephitmp_80; f[_137] = _139; which makes us conclude the f[_137] access is constrained to f[0..2]. When we see _75 = MEM[(int *)_20 + 16B]; we then disambiguate because iff _20 points into 'f' then with offset 16 it's beyond that constrained access. _But_! # RANGE [18446744065119617028, 18446744073709551608] _5 = _39 * -4U; # PT = anything _20 = &f + _5; _20 is actually _before_ 'f' which we consider invalid. Now here's what the frontend presents us with: f[4 - d] = f[4 - d] ^ 3; which we eventually gimplify to _5 = 4 - d.1_4; _6 = f[_5]; but then predictive commoning comes along: Load motion chain 0x43bb3d0 inits MEM[(int *)_20 + 16B] references: f[_2] (id 0) offset 0 distance 0 f[_2] (id 1, write) offset 0 distance 0 Executing predictive commoning without unrolling <bb 36> [local count: 35740571]: + _39 = (sizetype) prephitmp_80; + _5 = _39 * 18446744073709551612; + _20 = &f + _5; + _75 = MEM[(int *)_20 + 16B]; <bb 11> [local count: 289173710]: # ivtmp_48 = PHI <ivtmp_68(22), 7(36)> + # f_I_lsm0.27_12 = PHI <f_I_lsm0.27_1(22), _75(36)> _2 = 4 - prephitmp_80; - _3 = f[_2]; + _3 = f_I_lsm0.27_12; introducing this kind of problem. We have a "opt-out" with using TARGET_MEM_REF which is exempt from this rule because IVOPTs also likes to break it.
next prev parent reply other threads:[~2022-09-09 9:31 UTC|newest] Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-09-08 21:37 [Bug c/106892] New: Wrong code at -O3 on x86_64-linux-gnu shaohua.li at inf dot ethz.ch 2022-09-08 22:02 ` [Bug c/106892] " jakub at gcc dot gnu.org 2022-09-09 7:40 ` rguenth at gcc dot gnu.org 2022-09-09 7:53 ` shaohua.li at inf dot ethz.ch 2022-09-09 8:15 ` rguenth at gcc dot gnu.org 2022-09-09 8:20 ` marxin at gcc dot gnu.org 2022-09-09 8:20 ` jakub at gcc dot gnu.org 2022-09-09 8:31 ` [Bug c/106892] [11/12/13 Regression] Wrong code at -O3 on x86_64-linux-gnu since r11-963-g80d6f89e78fc3b77 rguenth at gcc dot gnu.org 2022-09-09 8:32 ` [Bug middle-end/106892] " rguenth at gcc dot gnu.org 2022-09-09 9:05 ` rguenth at gcc dot gnu.org 2022-09-09 9:31 ` rguenth at gcc dot gnu.org [this message] 2022-09-09 10:04 ` rguenth at gcc dot gnu.org 2022-09-09 12:43 ` rguenth at gcc dot gnu.org 2022-09-10 13:14 ` [Bug middle-end/106892] [11/12 " mikpelinux at gmail dot com 2022-09-12 7:53 ` marxin at gcc dot gnu.org 2022-10-11 12:06 ` cvs-commit at gcc dot gnu.org 2022-10-17 13:28 ` [Bug middle-end/106892] [11 " cvs-commit at gcc dot gnu.org 2022-10-17 13:29 ` rguenth at gcc dot gnu.org
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