#13282: Introduce fast path through simplifier for static bindings -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: feature | Status: new request | Priority: normal | Milestone: Component: Compiler | Version: 8.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Compile-time Unknown/Multiple | performance bug Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- It's not uncommon for early simplifier runs to float out a large number of "static data" bindings from a user program to the top-level. Here we will consider a top-level binding to be "static" if its RHS consists of a data constructor applied to zero or more other static bindings. This floating is quite helpful as static top-levels are represented easily as static code in object code. It also opens an interesting possibility: we know (with a few potential caveats discussed later) no further simplification of these bindings is possible. However, the simplifier currently does not take advantage of this latter fact: currently the simplifier will dutifully rebuild all bindings on every iteration. This work is wasted effort. I think it would be helpful to track the "static-ness" of top-level bindings and teach the simplifier and various analyses to ignore bindings so-marked. Also, there is one caveat here: it is currently possible for users to write rules whose LHSs are headed by a data constructor. This means that further simplification of the bindings which we deemed above as "static" **is** possible. There are two ways of dealing with this, a. Forbidding data cons in the head of a RULE's LHS b. Check the rule-base for matching rules matching a datacon as "static" -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13282 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler