[llvm-dev] Need help reproducing a bug

[Michael Zolotukhin via llvm-dev]

Thanks everyone! What are the best tools/techniques to expose such non-deterministic behavior? My hope is to reproduce it on a smaller test (e.g. use some sanitizer and thus make the compiler *fail* when building the test) - Currently these failures only tell me “there is some bug in your code” without any hints where to look for it.

Michael

> On Apr 18, 2018, at 9:18 PM, Steven Wu <stevenwu at apple.com> wrote:
> 
> 
> 
>> On Apr 18, 2018, at 9:11 AM, Roman Lebedev via llvm-dev <llvm-dev at lists.llvm.org> wrote:
>> 
>> On Wed, Apr 18, 2018 at 5:45 PM, Michael Zolotukhin via llvm-dev
>> <llvm-dev at lists.llvm.org> wrote:
>>> Hi,
>>> 
>>> Recently I committed a change (r330175) that passed all my testing, but
>>> failed on several bots. Namely, these are the failed ones:
>>> http://lab.llvm.org:8011/builders/clang-with-thin-lto-ubuntu/builds/9803
>>> http://lab.llvm.org:8011/builders/clang-with-lto-ubuntu/builds/8173
>>> http://lab.llvm.org:8011/builders/lld-x86_64-freebsd/builds/18082
>> Note what *specifically* failed:
>> * compare-compilers compare stage3 and stage4 compilers failed ( 0 secs )
>> * compare-tablegen-inc-files compare stage3 and stage4 Tablegen inc
>> files failed ( 1 secs )
>> 
>> I.e. it wasn't tests that failed.
> 
> Failing that tests means the compiler doesn't produce deterministic output because the stage3 and stage 4 compiler has to be the same.
> 
> Not sure about LLD test.
> 
> Steven
> 
>> 
>>> I reverted the change (r330180), but now I’m stuck with how to proceed with
>>> it, as I can’t reproduce any of these.
>>> 
>>> So far I’ve tried building clang with asan and using this sanitized clang to
>>> build clang and lld one more time and run make check - none of these failed
>>> on my machine. What else could I try to catch the issue?
>>> 
>>> In case you are interested in details and/or want to try to reproduce it,
>>> you’ll need to revert r330180 (and thus reapply r330175). The change is
>>> about using a new faster SSAUpdater in Jump Threading, more details are
>>> available in the phabricator: https://reviews.llvm.org/D44282.
>>> 
>>> Thanks,
>>> Michael
>>> 
>>> 
>>> 
>>> 
>>> _______________________________________________
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>>> llvm-dev at lists.llvm.org
>>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>> 
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