This adds an -enable-memcpyopt-memoryssa option that currently does nothing apart from requiring MSSA as a dependency. The tests are split to run both with the option disabled and enabled. I went with this rather than the separate directory DSE uses, as I found it convenient to have a direct side-by-side comparison of differences.
(The context is D90281)
Is this work in progress, meaning there are more patches coming adding coverage? So for example, in Transforms/MemCpyOpt/vscale-memset.ll, there's no NO_MSSA check right now, but there will be later, is that correct?
If D90281 applies, could you comment there about your scenario (i.e. had --check-prefixes been strict, how would this work have been impacted)? Thanks!
Also - could you take a look at http://lists.llvm.org/pipermail/llvm-dev/2020-October/146162.html, especially at the tests list - thanks!