|Version 13 (modified by nomeata, 18 months ago) (diff)|
This is nomeata’s notepad about the nested CPR information:
- #1600 Main tickets where I mention progress.
Tickets with stuff that would make nested CPR better:
- #8598 CPR after IO (partly done)
- Everything in source:testsuite/tests/stranal/sigs/
- Does Nick Frisby’s late λ-lifting alleviate problems when CPR’ing join-points?
- Paper-Writeup of CPR
- Shouldn’t nested CPR help a lot with Complex-heavy code? Is there something in nofib?
- Try passing CPR information from the scrunitee to the pattern variables. For that: Reverse flow of analysis for complex scrunitees (for simple, we want the demand coming from the body, for complex, this is not so important.)
- Use ticky-profiling to learn more about the effects of nested CPR.
- Look at DmdAnal-related [SLPJ-Tickets] and see which ones are affected by nested-cpr.
- Do not destroy join points (see below).
- Can we make sure more stuff gets the Converging flag, e.g. after a case of an unboxed value? Should case binders get the Converging flag? What pattern match variables in strict data constructors? Unboxed values?
CPR can kill join points.
Idea to fix this, and possibly more general benefits: http://www.haskell.org/pipermail/ghc-devs/2013-December/003481.html; prototype in branch wip/common-context.
- On its own, improvements are present but very small: http://www.haskell.org/pipermail/ghc-devs/2013-December/003500.html
- Enabling CPR for sum types in non-top-level-bindings (which is currently disabled due to worries abut lost join points) yields mixed results (min -3.8%, mean -0.0%, max 3.4%).
- Enabling sum types inside nested CPR: Also yields mixed, not very promising results (-6.9% / +0.0% / +11.3%).
Alternative: Detect join points during dmdAnal and make sure that their CPR info is not greater than that of the expression they are a join-point for. Would also fix #5075, see 5075#comment:19 for benchmark numbers.
- On its own, no changes.
- Enabling CPR for sumtypes: (min -3.8%, mean -0.0%, max 1.7%) (slightly better than with Common Context)
- Enabling sum types inside nested CPR: TBD