#12915: cmmImplementSwitchPlans creates duplicate blocks -------------------------------------+------------------------------------- Reporter: alexbiehl | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by Ben Gamari <ben@…>): In [changeset:"d5c4d46a62ce6a0cfa6440344f707136eff18119/ghc" d5c4d46a/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="d5c4d46a62ce6a0cfa6440344f707136eff18119" 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 }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12915#comment:11> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler