[Bug gcov-profile/67937] gcov gives wrong results when negative counts are involved

[Bug gcov-profile/67937] gcov gives wrong results when negative counts are involved

[Pidgeot18 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67937

--- Comment #1 from Joshua Cranmer <Pidgeot18 at gmail dot com> ---
Created attachment 36485
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=36485&action=edit
test-case.gcda

(It's a 4.7 test case, but the file format can still be read with trunk gcov
the last I checked. Since the originating issue comes from "compile Firefox", I
haven't tried preparing .gcda/.gcno files from newer gcc).

[Bug gcov-profile/67937] gcov gives wrong results when negative counts are involved

[Pidgeot18 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67937

--- Comment #2 from Joshua Cranmer <Pidgeot18 at gmail dot com> ---
Created attachment 36486
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=36486&action=edit
test-case.gcno

And the corresponding .gcno file.

The testcase was minimized by bisecting the original .gcda/.gcno files by
dropping functions and seeing where my attempt to write a new implementation
that matched gcov's output failed. The attempt (I did several!) that failed
this time was using Boost graph library's hawick_circuits detector, which
matched the input incorrectly since this is double-counting loop edges if one
of them is negative.

[Bug gcov-profile/67937] gcov gives wrong results when negative counts are involved

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67937

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
Most interesting would be a C testcase that produces the CFG with the bogus
counters ;)