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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/99966] Bounds check not eliminated by assert Date: Tue, 11 Jan 2022 18:59:33 +0000 [thread overview] Message-ID: <bug-99966-4-2zvytVquVQ@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-99966-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99966 Andrew Macleod <amacleod at redhat dot com> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |amacleod at redhat dot com --- Comment #2 from Andrew Macleod <amacleod at redhat dot com> --- looking at VRP2: the initial assert provides: Relational : (start_4(D) < end_5(D)) Relational : (_16 > start_4(D)) Relational : (end_5(D) <= _16) unfortunately, the loop back edge is: i_12 = i_17 + 1; if (end_5(D) != i_12) goto <bb 5>; [89.00%] else goto <bb 8>; [11.00%] so it only registers what it knows from the branch: Relational : (i_12 != end_5(D)) so when it gets to the bounds check at: if (i_12 >= _16) goto <bb 6>; [0.04%] else goto <bb 10>; [99.96%] It doesn't really know the answer. If the loop branch had remained if (i_12 < end_5) instead of being changed, then we would instead get the relation: Relational : (i_12 < end_5(D)) which combined with the earlier Relational : (end_5(D) <= _16), should register the transitive relation (i_12 < _16), and enable removal of the check. This is transformed in ivopts, which runs after vrp1. A quick check shows at VRP1 time, the bounds are still using the < format... In fact... running with --param=vrp1-mode=ranger registers this exact transitive relation, and produces: Relational : (i_2 < _16) Relational : (i_2 < end_5(D)) <bb 6> [local count: 952547451]: if (0 != 0) goto <bb 7>; [0.04%] else goto <bb 8>; [99.96%] and eliminates the bounds check. So we can close this PR when we turn ranger on by default for VRP1.
next prev parent reply other threads:[~2022-01-11 18:59 UTC|newest] Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-04-08 1:23 [Bug tree-optimization/99966] New: " jmuizelaar at mozilla dot com 2021-04-08 7:19 ` [Bug tree-optimization/99966] " rguenth at gcc dot gnu.org 2022-01-11 18:59 ` amacleod at redhat dot com [this message] 2022-11-03 19:31 ` amacleod at redhat dot com 2022-11-28 22:09 ` pinskia at gcc dot gnu.org
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