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From: "amacleod at redhat dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug tree-optimization/103721] [12 regression] wrong code generated for loop with conditional since r12-4790-g4b3a325f07acebf4 Date: Thu, 20 Jan 2022 14:12:03 +0000 [thread overview] Message-ID: <bug-103721-4-JrPdZdpR7M@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-103721-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103721 --- Comment #14 from Andrew Macleod <amacleod at redhat dot com> --- (In reply to Aldy Hernandez from comment #11) > <bb 3> [local count: 1063004409]: > # j_17 = PHI <j_2(9), 0(2)> > # q_18 = PHI <prephitmp_16(9), &a(2)> > > <bb 5> [local count: 1063004409]: > # j_2 = PHI <j_8(4), 0(3)> > # prephitmp_16 = PHI <_14(4), &a(3)> > if (prephitmp_16 == q_18) > goto <bb 6>; [0.00%] > else > goto <bb 7>; [100.00%] > > <bb 9> [local count: 1052374367]: > goto <bb 3>; [100.00%] > > Even if we reset relations and clear the root oracle at the backedge (9->3), > we still get the _16 == _18 in BB3, followed by the DEF of _16 in BB5. Well, you cant add that relation either.. although you have cleared the existing relations when you traverse the back edge, you are then immediately adding another one FROM the backedge (9->3) which is a value from the previous iteration... so it cant be used. You need to also stipulate that if you are adding an equivalence from a PHI like that, it is not a back edge you are adding from. And I think it is probably safe to "reset" the root oracle to search for relations from top of the loop, assuming it dominates the latch it came from. Any new relations are going to now be dominated by this block.
next prev parent reply other threads:[~2022-01-20 14:12 UTC|newest] Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-12-14 22:19 [Bug tree-optimization/103721] New: [12 regression] wrong code generated for loop with conditional (jump threading?) sss@li-snyder.org 2021-12-14 22:21 ` [Bug tree-optimization/103721] " pinskia at gcc dot gnu.org 2021-12-14 23:03 ` pinskia at gcc dot gnu.org 2021-12-15 11:27 ` [Bug tree-optimization/103721] [12 regression] wrong code generated for loop with conditional since r12-4790-g4b3a325f07acebf4 marxin at gcc dot gnu.org 2022-01-04 11:16 ` rguenth at gcc dot gnu.org 2022-01-06 20:13 ` amacleod at redhat dot com 2022-01-18 4:02 ` law at gcc dot gnu.org 2022-01-18 18:49 ` amacleod at redhat dot com 2022-01-19 12:44 ` aldyh at gcc dot gnu.org 2022-01-19 16:40 ` aldyh at gcc dot gnu.org 2022-01-19 16:58 ` amacleod at redhat dot com 2022-01-19 22:51 ` law at gcc dot gnu.org 2022-01-20 0:10 ` amacleod at redhat dot com 2022-01-20 11:13 ` aldyh at gcc dot gnu.org 2022-01-20 11:14 ` aldyh at gcc dot gnu.org 2022-01-20 13:28 ` aldyh at gcc dot gnu.org 2022-01-20 14:12 ` amacleod at redhat dot com [this message] 2022-01-21 10:19 ` cvs-commit at gcc dot gnu.org 2022-01-21 10:30 ` aldyh at gcc dot gnu.org
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