CmmPipeline: add a second pass of CmmCommonBlockElim
The sinking pass often gets rid of unnecessary registers registers/assignements exposing more opportunities for CBE, so this commit adds a second round of CBE after the sinking pass and should fix #12915 (and some examples in #14226). Nofib results: * Binary size: 0.9% reduction on average * Compile allocations: 0.7% increase on average * Runtime: noisy, two separate runs of nofib showed a tiny reduction on average, (~0.2-0.3%), but I think this is mostly noise * Compile time: very noisy, but generally within +/- 0.5% (one run faster, one slower) One interesting part of this change is that running CBE invalidates results of proc-point analysis. But instead of re-doing the whole analysis, we can use the map that CBE creates for replacing/comparing block labels (maps a redundant label to a useful one) to update the results of proc-point analysis. This lowers the overhead compared to the previous experiment in #12915. Signed-off-by:Michal Terepeta <michal.terepeta@gmail.com> Test Plan: ./validate Reviewers: bgamari, simonmar Reviewed By: simonmar Subscribers: rwbarton, thomie, carter GHC Trac Issues: #12915, #14226 Differential Revision: https://phabricator.haskell.org/D4417
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