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From: "mikael at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/111293] [14 Regression] Missed Dead Code Elimination since r14-3414-g0cfc9c953d0 Date: Tue, 09 Apr 2024 09:38:09 +0000 [thread overview] Message-ID: <bug-111293-4-qS5J6kEz6N@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-111293-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111293 Mikael Morin <mikael at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |mikael at gcc dot gnu.org --- Comment #3 from Mikael Morin <mikael at gcc dot gnu.org> --- pre replaces usages of the 'e' global with a set of 'pretmp' and 'prephitmp' ssa registers. With gcc-13, the value of 'e' is reloaded directly after the call to 'foo', and that value is joined with a phi in the next bb: <bb 10> [local count: 7761689018]: foo (); pretmp_25 = e; goto <bb 15>; [100.00%] ... <bb 15> [local count: 8963573811]: # j_28 = PHI <1(10), j_30(24), 1(22), j_30(25), 1(26), j_30(20)> # i_29 = PHI <i_20(10), 0(24), i_19(22), 0(25), i_21(26), 0(20)> # prephitmp_38 = PHI <pretmp_25(10), prephitmp_26(24), prephitmp_26(22), prephitmp_26(25), prephitmp_26(26), prephitmp_26(20)> d.7_22 = d; _23 = d.7_22 + 1; d = _23; if (_23 != 0) goto <bb 27>; [94.50%] else goto <bb 18>; [5.50%] With gcc-14, the value of 'e' is reloaded later in the next bb, causing a dependency on 'e', even on paths not calling 'foo': <bb 5> [local count: 7761689018]: foo (); goto <bb 8>; [100.00%] ... <bb 8> [local count: 8963573796]: # i_28 = PHI <i_13(5), 0(12), i_13(15)> d.7_22 = d; _23 = d.7_22 + 1; d = _23; pretmp_10 = e; if (_23 != 0) goto <bb 17>; [94.50%] else goto <bb 11>; [5.50%] Later on this prevents copyprop from simplifying the 'pretmp' and 'prephitmp' values to 3 and remove the branch calling 'foo'.
next prev parent reply other threads:[~2024-04-09 9:38 UTC|newest] Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top 2023-09-05 15:01 [Bug tree-optimization/111293] New: " theodort at inf dot ethz.ch 2023-09-05 17:25 ` [Bug tree-optimization/111293] " pinskia at gcc dot gnu.org 2023-09-05 17:40 ` pinskia at gcc dot gnu.org 2023-09-05 17:40 ` pinskia at gcc dot gnu.org 2023-11-24 15:56 ` amacleod at redhat dot com 2024-03-07 23:21 ` law at gcc dot gnu.org 2024-04-09 9:38 ` mikael at gcc dot gnu.org [this message] 2024-04-09 9:47 ` mikael at gcc dot gnu.org 2024-05-07 7:41 ` [Bug tree-optimization/111293] [14/15 " rguenth at gcc dot gnu.org
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