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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
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