#15001: Add strict product field demands to lambda binders -------------------------------------+------------------------------------- Reporter: sgraf | Owner: (none) Type: task | Status: new Priority: normal | Milestone: ⊥ Component: Compiler | Version: 8.5 Keywords: DmdAnal | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): D4244 | Wiki Page: -------------------------------------+------------------------------------- This is a follow-up on the first improvement in [Phab:D4244#126311]. Consider the following two functions with identical semantics: {{{ module Foo where {-# LANGUAGE BangPatterns #-} data Complex a = !a :+ !a foo :: Complex Double -> Int -> Complex Double foo !x 0 = x foo (a :+ b) _ = b :+ a bar :: Complex Double -> Int -> Complex Double bar x 0 = x bar (a :+ b) _ = b :+ a }}} In the corresponding simplified Core, `x` gets strictness `S(SS)` for `foo`, but only `S` for `bar`. We could do better by looking at `x`s type and see that its a product type with strict fields. This is because currently only case binders get [https://github.com/ghc/ghc/blob/72b5f649ede82ab3bb429aa72ee1c572f415b0eb/com... special treatment] for strict product fields through `addDataConStrictness`. This ticket tracks if the same is worthwhile for lambda binders, as in `bar` above. Note that intuitively, this shouldn't make any difference because when we eventually unleash an `S` demand on a `Complex` constructor, we add `seqDmd` on strict fields anyway, amounting to `S(SS)`. So this is only a matter of recording things early because some parts of the analysis code might not be smart enough to add strict field demands by themselves. Also note that this doesn't touch impliciations on usage analysis at all, where unleashing the same `seqDmd` twice might mean we accidentally make some product field lose its single-entrieness. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15001 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler