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
