[polly] r305633 - Add information about bisecting

[Davide Italiano via llvm-commits]

On Sat, Jun 17, 2017 at 1:04 AM, Davide Italiano <davide at freebsd.org> wrote:
> On Sat, Jun 17, 2017 at 12:45 AM, Tobias Grosser via llvm-commits
> <llvm-commits at lists.llvm.org> wrote:
>> Author: grosser
>> Date: Sat Jun 17 02:45:44 2017
>> New Revision: 305633
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=305633&view=rev
>> Log:
>> Add information about bisecting
>>
>> Modified:
>>     polly/trunk/docs/TipsAndTricks.rst
>>
>> Modified: polly/trunk/docs/TipsAndTricks.rst
>> URL: http://llvm.org/viewvc/llvm-project/polly/trunk/docs/TipsAndTricks.rst?rev=305633&r1=305632&r2=305633&view=diff
>> ==============================================================================
>> --- polly/trunk/docs/TipsAndTricks.rst (original)
>> +++ polly/trunk/docs/TipsAndTricks.rst Sat Jun 17 02:45:44 2017
>> @@ -37,3 +37,16 @@ Understanding which pass makes a particu
>>      - ``$ opt -O3 -polly -debug-pass=Arguments`` to get all passes that are run by default. ``-debug-pass=Arguments`` will list all passes that have run.
>>      - Bisect down to the pass that changes it.
>>
>> +
>> +Debugging regressions introduced at some unknown earlier point
>> +--------------------------------------------------------------
>> +
>> +In case of a regression in performance or correctness (e.g., an earlier version
>> +of Polly behaved as expected and a later version does not), bisecting over the
>> +version history is the standard approach to identify the commit that introduced
>> +the regression.
>> +
>> +LLVM has a single repository that contains all projects. It can be cloned at:
>> +`<https://github.com/llvm-project/llvm-project-20170507>`_. How to bisect on a
>> +git repository is explained here
>> +`<https://www.metaltoad.com/blog/beginners-guide-git-bisect-process-elimination`.
>>
>
> Hi Tobias,
> the article you link describes a semi-manual procedure for bisecting.
> I think something better can be done in case you have a test of what
> fails using `git bisect run`. I created a gist because I kept
> forgetting how to do it :) (in particular the return code being `125`
> in case of "dubious" revisions).
> https://gist.github.com/dcci/891cd98d80b1b95352a407d80914f7cf
>
> I also found this useful when reducing regressions:
> https://gcc.gnu.org/wiki/A_guide_to_testcase_reduction
>
> --
> Davide
>
> "There are no solved problems; there are only problems that are more
> or less solved" -- Henri Poincare

There's also another article from the same website:
https://www.metaltoad.com/blog/mechanizing-git-bisect-bug-hunting-lazy

-- 
Davide

"There are no solved problems; there are only problems that are more
or less solved" -- Henri Poincare