• Georgios Karachalias's avatar
    Adding flags: -ffull-guard-reasoning and too-many-guards · bec5350d
    Georgios Karachalias authored
    Introduction of two new flags, for more precise control over the new
    pattern match checker's behaviour when reasoning about guards. This is
    supposed to address #11195 (and maybe more performance bugs related to
    the NP-Hardness of coverage checking).
    Expected behaviour:
      * When `-ffull-guard-reasoning` is on, run the new pattern match
        checker in its full power
      * When `-ffull-guard-reasoning` is off (the default), for every
        match, check a metric to see whether pattern match checking for it
        has high probability of being non performant (at the the moment we
        check whether the number of guards is over 20 but I would like to
        use a more precise measure in the future). If the probability is
        - Oversimplify the guards (less expressive but more performant)
          and run the checker, and
        - Issue a warning about the simplification that happened.
    A new flag `-Wtoo-many-guards/-Wno-too-many-guards` suppresses the
    warning about the simplification (useful when combined with -Werror).
    Test Plan: validate
    Reviewers: goldfire, austin, hvr, bgamari
    Reviewed By: bgamari
    Subscribers: mpickering, thomie
    Differential Revision: https://phabricator.haskell.org/D1676
    GHC Trac Issues: #11195
OptCoercion.hs 32.5 KB