-
Simon Peyton Jones authored
Triggered by #12150, and the knock-on effects of join points, I did a major refactoring of the Simplifier. This is a big patch that change a lot of Simplify.hs: I did a lot of other re-organisation. The main event ~~~~~~~~~~~~~~ Since the dawn of time we have had simplExpr :: SimplEnv -> InExpr -> SimplCont -> SimplM (SimplEnv, OutExpr) What's that SimplEnv in the result? When simplifying an expression the simplifier add floated let-bindings to the SimplEnv, extending the in-scope set appropriately, and hence needs to resturn the SimplEnv at the end. The mode, flags, substitution in the returned SimplEnv were all irrelevant: it was just the floating bindings. It's strange to accumulate part of the /result/ in the /environment/ argument! And indeed its leads to all manner of mysterious calls to zapFloats and transferring of floats from one SimplEnv to another. It got worse with join points, so I finally bit the bullet and refactored. Now we have simplExpr :: SimplEnv -> InExpr -> SimplCont -> SimplM (SimplFloats, OutExpr) -- See Note [The big picture] and the SimplEnv no longer has floats in it. The code is no shorter, but it /is/ easier to understand. Main changes * Remove seLetFloats field from SimplEnv * Define new data type SimplFloats, and functions over it * Change the types of simplExpr, simplBind, and their many variants, to follow the above plan Bottoming bindings ~~~~~~~~~~~~~~~~~~ I made one other significant change in SimplUtils (not just refactoring), related to Trac #12150 comment:16. Given x = <rhs> where <rhs> turns out to be a bottoming expression, propagate that information to x's IdInfo immediately. That's always good, because it makes x be inlined less (we don't inline bottoming things), and it allows (case x of ...) to drop the dead alterantives immediately. Moreover, we are doing the analysis anyway, in tryEtaExpandRhs, which calls CoreArity.findRhsArity, which already does simple bottom analysis. So we are generating the information; all we need do is to atach the bottoming info to the IdInfo. See Note [Bottoming bindings] Smaller refactoring ~~~~~~~~~~~~~~~~~~~ * Rename SimplifierMode to SimplMode * Put DynFlags as a new field in SimplMode, to make fewer monadic calls to getDynFlags. * Move the code in addPolyBind into abstractFloats * Move the "don't eta-expand join points" into tryEtaExpandRhs
33452dfc