Misc. progress

• Rename TightAssociative to MonoidReduce.
• Lower phis, reads, and writes in RT backend.
• Allow fork fission to not take in an explicit data label - in this case, implicitly the fission point is between the parallel section and the reduction cycle (this is the most common case).
• CleanMonoidReduces pass which makes outer forks around monoid reductions more easily parallelizable after fission.
• Fix GCM behavior w/ primitive constants / undefs.
• Make SimplifyCFG more aggressive with removing reduces (motivated by fission).
• Add UnforkifyOne pass, which only unforkifies the first loop it sees - useful for unforkifying outer loops.
• Multi-core dot product test that uses a bunch of the stuff in this MR.
• A whole bunch of fixes.

assigned to @rarbore2

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• 5a1fa18b - Lower read and write in rt backend

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• 85ce14bd - enough rt backend stuff for multi-threaded dot

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marked this merge request as ready

changed title from Draft: CPU Vector backend to Misc. progress

changed the description

requested review from @aaronjc4

merged

mentioned in commit 410e0ec7