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From: "aldyh at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug middle-end/106495] [13 Regression] Build fails gcc/tree-ssa-threadbackward.cc:22: gcc/vec.h:890:19: error: array subscript 4294967294 is above array bounds of 'basic_block_def* [1]' [-Werror=array-bounds] Date: Mon, 01 Aug 2022 13:58:08 +0000 [thread overview] Message-ID: <bug-106495-4-NlNQDrJGuO@http.gcc.gnu.org/bugzilla/> (raw) In-Reply-To: <bug-106495-4@http.gcc.gnu.org/bugzilla/> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106495 --- Comment #9 from Aldy Hernandez <aldyh at gcc dot gnu.org> --- (In reply to Richard Biener from comment #7) > So in this case we have > > (gdb) p *path->m_vec->m_vecdata[0] > $106 = {e = <edge 0xf4819a40 (5 -> 7)>, type = EDGE_COPY_SRC_BLOCK} > (gdb) p *path->m_vec->m_vecdata[1] > $107 = {e = <edge 0xf48199a0 (7 -> 9)>, type = EDGE_COPY_SRC_BLOCK} > (gdb) p *path->m_vec->m_vecdata[2] > $108 = {e = <edge 0xf48197e0 (9 -> 10)>, type = EDGE_NO_COPY_SRC_BLOCK} > > and the last edge (9 -> 10) is known to be never executed: > > <bb 9> [local count: 435262723]: > _3 = MEM <struct vec> [(struct basic_block_def * const &)_21].m_vecdata[_2]; > _4 = iftmp.22_23 + 4294967295; > if (_4 >= _20) > goto <bb 10>; [0.00%] > > we've isolated a quite "unlikely" combo here. We could go for generalizing > the earlier patch, disqualifying the path if any of the edges involved. > > Note that profitable_path_p only gets to see 5->7->9, strangely not the > final ->10? It look like only maybe_register_path () via find_taken_edge > will ask profitable_path_p _again_ (but with taken_edge now set)!? profitable_path_p gets called during path discovery (find_paths_to_names), so we don't have complete info. The idea is that if a path so far is unprofitable, no sense looking further in that particular direction. In reality Jeff and I ran into a testcase where a partial path was not profitable, but a path with some extra blocks was. There's a PR somewhere for it, but it happened so infrequent, that this heuristic was good enough. > > So the "cheapest" way to tackle this particular case is look at taken_edge > in profitable_path_p. I would've prefered putting everything in your previous patch, since it would be shared between both threaders, though I suppose the forward threader is slowly dying ;-).
next prev parent reply other threads:[~2022-08-01 13:58 UTC|newest] Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-08-01 6:29 [Bug middle-end/106495] New: " slyfox at gcc dot gnu.org 2022-08-01 8:38 ` [Bug middle-end/106495] " pinskia at gcc dot gnu.org 2022-08-01 9:22 ` rguenth at gcc dot gnu.org 2022-08-01 11:51 ` rguenth at gcc dot gnu.org 2022-08-01 12:17 ` rguenth at gcc dot gnu.org 2022-08-01 12:21 ` rguenth at gcc dot gnu.org 2022-08-01 12:33 ` rguenth at gcc dot gnu.org 2022-08-01 12:58 ` rguenth at gcc dot gnu.org 2022-08-01 13:04 ` rguenth at gcc dot gnu.org 2022-08-01 13:58 ` aldyh at gcc dot gnu.org [this message] 2022-08-02 6:35 ` cvs-commit at gcc dot gnu.org 2022-08-02 6:35 ` rguenth at gcc dot gnu.org
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