Re: [creduce-dev] A reduction attempt that creduce handled poorly, where delta was able to make progress

[John Regehr <regehr@cs.utah.edu>]

> Ah. I should have mentioned that I needed to use delta's -in_place
> option to get delta to work. Does creduce have an equivalent or do I
> have to manually do the backups and restoration on any build or test
> failure?

To support parallelism I removed C-Reduce's ability to reduce in place, 
you'll need to manually copy variants to whatever directory they should 
be in.

> With some iterations of delta, manually removing unused functions, and
> speculatively removing different arguments or calls I was able to get
> a copy of SLPVectorizer.cpp down to 102 lines (though still
> #include'ing 5 of the llvm headers) that gives the known-good result
> with the good switch and segfaults with the bad, but it might also be
> so small or full of UB that it isn't meaningful to determine what's
> getting miscompiled. I'm not sure at this point.
>
> Maybe if creduce had something like an in-place option to automate
> this type of situation where there's an external build system that has
> an absolute path to the file hard-coded, I would have gotten more
> mileage out of it here.

Maybe!  But basically it's very difficult to reduce a file that is part 
of something like a compiler in a sensible way.  It may be better to 
approach this problem another way.

John