1. 28 Feb, 2017 1 commit
    • rwbarton's avatar
      When floating, don't box an expression that's okay for speculation (#13338) · d0508ef0
      rwbarton authored
      Commit 432f952e (Float unboxed expressions by boxing) lets the float-out pass
      turn, for example,
      
          ... (-# (remInt# x# 100000#) i#) ...
      
      into
      
          let lvl :: Int
              lvl = case remInt# x# 100000# of v { __DEFAULT__ -> I# v }
          in ... (-# (case lvl of { I# v -> v }) i#) ...
      
      But when, as in the example above, the expression that was floated out was
      the argument of an application, the resulting application may no longer
      satisfy the let/app invariant, because exprOkForSpeculation doesn't look
      far enough inside the definition of lvl.
      
      Solution: When the expression we floated out was okay for speculation, don't
      bother boxing it. It will be evaluated earlier, and that's okay by assumption.
      Fixes the let/app invariant and is cheaper too.
      
      Test Plan: make slowtest TEST=T13338
      
      Reviewers: austin, bgamari, simonpj
      
      Reviewed By: bgamari, simonpj
      
      Subscribers: thomie
      
      Differential Revision: https://phabricator.haskell.org/D3217
      d0508ef0