[GHC] #1600: Optimisation: CPR the results of IO
GHC
ghc-devs at haskell.org
Mon Feb 20 09:19:25 UTC 2017
#1600: Optimisation: CPR the results of IO
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Reporter: simonmar | Owner: (none)
Type: task | Status: new
Priority: lowest | Milestone:
Component: Compiler | Version: 6.6.1
Resolution: | Keywords:
Operating System: Unknown/Multiple | Architecture:
Type of failure: Runtime | Unknown/Multiple
performance bug | Test Case:
Blocked By: | Blocking:
Related Tickets: #8598 | Differential Rev(s):
Wiki Page: |
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Comment (by simonpj):
> The main difference seems to come from this change...
Interesting! There are two changes in that commit:
* Making data con wrappers have `ug_unsat_ok = unSaturatedOk`. I buy
this. Can you try the effect of this change alone? It's entirely unrelated
to nested-CPR. It would be good to isolate that perf bump from the perf
changes due to nested CPR.
* Making data con wrapper have `ug_boring_ok = boringCxtOk`. I'm not sure
I buy this in full. In `Note [Inline data constructor wrappers
aggresively]` there's a claim that we get better nested-CPR info. That's
true if we have a polymorphic bang argument (e.g. `data T a = MkT !a`) but
for a monomorphic one like `data S = MkS !Int` we'll unpack it.
So I think the benefit comes only for polymorphic bangs. And there is a
cost to aggressive inlining, so we don't want to do it gratuitously.
--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/1600#comment:65>
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