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From: "rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/104543] [12 Regression] wrong code at -O3 on x86_64-linux-gnu Date: Tue, 15 Feb 2022 10:02:04 +0000 [thread overview] Message-ID: <bug-104543-4-7vNGKoyGUP@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-104543-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104543 Richard Biener <rguenth at gcc dot gnu.org> changed: What |Removed |Added ---------------------------------------------------------------------------- Status|NEW |ASSIGNED Assignee|unassigned at gcc dot gnu.org |rguenth at gcc dot gnu.org --- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> --- The issue is that we call do_rpo_vn without having SSA form updated and thus we see <bb 5> [local count: 90350471]: # c.4_22 = PHI <0(4), _40(24)> _8 = a[c.4_22]; _9 = _8 ^ 1; a[c.4_22] = _9; _10 = c.4_22 + 1; <bb 6> [local count: 11166912]: _16 = 3; _12 = b.6_23 + 1; <bb 22> [local count: 11166912]: # b.6_33 = PHI <_12(20)> <bb 23> [local count: 90350471]: # c.4_35 = PHI <c.4_22(22)> _37 = a[c.4_35]; _38 = _37 ^ 1; a[c.4_35] = _38; _40 = c.4_35 + 1; if (_40 <= 2) goto <bb 24>; [89.00%] else goto <bb 25>; [11.00%] but I think the PHI use in bb 23 will be _10 after updating SSA. Though need_ssa_update_p is false - tree_unroll_loop will call update SSA. Ah, after unroll but before fuse we have <bb 5> [local count: 90350471]: # c.4_22 = PHI <_10(10), 0(4)> and <bb 23> [local count: 90350471]: # c.4_35 = PHI <0(22), _40(24)> we've changed how CFG copying may alter PHI args. fuse_loops does /* The PHI nodes of the second body (single-argument now) need adjustments to use the right values: either directly the value of the corresponding PHI in the first copy or the one leaving the first body which unrolling did for us. See also unroll_jam_possible_p() for further possibilities. */ gphi_iterator psi_first, psi_second; e = single_pred_edge (next->header); for (psi_first = gsi_start_phis (loop->header), psi_second = gsi_start_phis (next->header); !gsi_end_p (psi_first); gsi_next (&psi_first), gsi_next (&psi_second)) { that we can iterate PHI args in lock-step this way is not guaranteed.
next prev parent reply other threads:[~2022-02-15 10:02 UTC|newest] Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-02-15 6:56 [Bug tree-optimization/104543] New: " zhendong.su at inf dot ethz.ch 2022-02-15 6:57 ` [Bug tree-optimization/104543] " zhendong.su at inf dot ethz.ch 2022-02-15 7:06 ` [Bug tree-optimization/104543] [12 Regression] " pinskia at gcc dot gnu.org 2022-02-15 7:14 ` pinskia at gcc dot gnu.org 2022-02-15 8:28 ` rguenth at gcc dot gnu.org 2022-02-15 10:02 ` rguenth at gcc dot gnu.org [this message] 2022-02-15 11:26 ` rguenth at gcc dot gnu.org 2022-02-15 12:22 ` cvs-commit at gcc dot gnu.org 2022-02-15 12:22 ` rguenth at gcc dot gnu.org 2022-02-15 12:23 ` [Bug tree-optimization/104543] [9/10/11 " rguenth at gcc dot gnu.org 2022-02-15 12:53 ` rguenth at gcc dot gnu.org 2022-02-15 12:54 ` rguenth at gcc dot gnu.org 2022-02-15 14:47 ` matz at gcc dot gnu.org 2022-05-27 9:47 ` [Bug tree-optimization/104543] [10/11 " rguenth at gcc dot gnu.org 2022-06-28 10:48 ` jakub at gcc dot gnu.org 2022-07-15 10:51 ` marxin at gcc dot gnu.org 2023-07-07 10:42 ` [Bug tree-optimization/104543] [11 " rguenth at gcc dot gnu.org
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