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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/97623] [9/10/11 Regression] Extremely slow O2 compile (>>O(n^2)) Date: Fri, 30 Oct 2020 12:35:39 +0000 [thread overview] Message-ID: <bug-97623-4-lnSyb1jwEP@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-97623-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97623 --- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> --- OK, so we have PRE and hoist insertion exposing new opportunities to each other, making things tickle up the CFG. Then, the way hoist insertion works it would be better suited to a bottom-up walk since hoist inserts may expose new hoist candidates - but a bottom-up walk makes updating AVAIL_OUT sets harder. The following pattern requires N hoist insert iterations for example: void baz(); int tem; void foo (int a, int b, int c, int d, int e, int x, int y) { if (a) { if (b) { if (c) { tem = x + y; } else { if (d) baz (); tem = x + y; } } else { if (d) baz (); tem = x + y; } } else { if (d) baz (); tem = x + y; } } now, due to PRE insertion and hoist insertion going in different directions the cascading cannot be avoided in general. But I think we can improve things by first doing hoist insertion backwards (no need to propagate NEW sets there) and then doing PRE insertion forward, propagating NEW sets on the fly. That makes the above testcase take 2 iterations and your original testcase "only" 94. As said, the back-to-back cannot really be avoided but the wrong order hoist insertion can be fixed.
next prev parent reply other threads:[~2020-10-30 12:35 UTC|newest] Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-10-29 2:02 [Bug c++/97623] New: " wsnyder at wsnyder dot org 2020-10-29 2:03 ` [Bug c++/97623] " wsnyder at wsnyder dot org 2020-10-29 7:17 ` [Bug tree-optimization/97623] [9/10/11 Regression] " rguenth at gcc dot gnu.org 2020-10-29 7:18 ` rguenth at gcc dot gnu.org 2020-10-30 12:35 ` rguenth at gcc dot gnu.org [this message] 2020-10-30 12:35 ` rguenth at gcc dot gnu.org 2020-10-30 13:25 ` cvs-commit at gcc dot gnu.org 2020-10-30 13:28 ` rguenth at gcc dot gnu.org 2020-10-30 13:55 ` wsnyder at wsnyder dot org 2020-11-03 14:16 ` rguenth at gcc dot gnu.org 2020-11-03 15:23 ` cvs-commit at gcc dot gnu.org 2020-11-06 1:50 ` wsnyder at wsnyder dot org 2020-11-06 9:52 ` rguenther at suse dot de 2020-11-06 12:37 ` wsnyder at wsnyder dot org 2020-11-06 13:00 ` rguenth at gcc dot gnu.org 2020-11-06 13:19 ` marxin at gcc dot gnu.org 2020-11-06 13:28 ` rguenth at gcc dot gnu.org 2020-11-06 13:45 ` rguenth at gcc dot gnu.org 2020-11-11 11:51 ` cvs-commit at gcc dot gnu.org 2020-11-11 16:11 ` tschwinge at gcc dot gnu.org 2020-11-11 17:17 ` cvs-commit at gcc dot gnu.org 2020-12-07 13:03 ` [Bug tree-optimization/97623] [9/10 " rguenth at gcc dot gnu.org 2021-01-11 13:37 ` cvs-commit at gcc dot gnu.org 2021-01-11 13:37 ` cvs-commit at gcc dot gnu.org 2021-01-11 13:39 ` [Bug tree-optimization/97623] [9 " rguenth at gcc dot gnu.org 2021-06-01 8:18 ` rguenth at gcc dot gnu.org 2022-05-27 8:56 ` rguenth at gcc dot gnu.org
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