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From: "marxin at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug gcov-profile/91601] gcov: ICE in handle_cycle, at gcov.c:699 happen which get code coverage with lcov.
Date: Mon, 19 Oct 2020 12:17:33 +0000	[thread overview]
Message-ID: <bug-91601-4-ilfRt7gbl7@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-91601-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91601

--- Comment #18 from Martin Liška <marxin at gcc dot gnu.org> ---
(In reply to Fangrui Song from comment #17)
> The algorithm is Donald B. Johnson's "Finding all the elementary circuits of
> a directed graph" (1975). (Hawick and James's just implemented the same
> algorithm by changing the representation of graphs).
> 
> I am wondering why we enumerate every elementary cycle, find the minimum
> edge, reduce edge weighs, and repeat the process.

I basically taken the original patch submission and finished it.

> 
> What do we lose if we don't use the costly algorithm? (The time complexity
> is O(n*e*(c+1)). However, many implementations (Boost and gcov.c) do not use
> a hash set for the blocked list, and thus I suspect the actual complexity is
> higher). Do we have other low-cost approaches? (e.g. repeatedly finding
> strongly connected components and reducing)

Do you have a test-case where it is significant?
Feel free to provide a patch which can make it faster, I'll appreciate and
review it.

      parent reply	other threads:[~2020-10-19 12:17 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <bug-91601-4@http.gcc.gnu.org/bugzilla/>
2020-03-27 19:28 ` mpolacek at gcc dot gnu.org
2020-03-29 14:19 ` marxin at gcc dot gnu.org
2020-03-29 17:19 ` cvs-commit at gcc dot gnu.org
2020-03-29 17:20 ` marxin at gcc dot gnu.org
2020-09-16  1:09 ` i at maskray dot me
2020-10-19 12:17 ` marxin at gcc dot gnu.org [this message]

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