#5954: Performance regression 7.0 -> 7.2 (still in 7.4)
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Reporter: simonmar | Owner: simonpj
Type: bug | Status: new
Priority: high | Milestone: 7.4.2
Component: Compiler | Version: 7.4.1
Keywords: | Os: Unknown/Multiple
Architecture: Unknown/Multiple | Failure: Runtime performance bug
Difficulty: Unknown | Testcase:
Blockedby: | Blocking:
Related: |
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Comment(by simonmar):
Further on this: we discovered that there are two things going on, neither
of which is #5623.
* Some fusion isn't happening on a `map f [x,y..z]` because the list is
being floated out before the RULE can fire. Simon is looking into
declaring `enumFromTo` and friends as `CONLIKE`, which might fix this
problem. (this regression first appeared in 7.0; the fusion ''did''
happen in 6.12.3)
* There is an opportunity for CSE which 7.0 spots but later versions
don't. It is probably a bug in `blackscholes.hs` itself:
{{{
nofXd1 = cndf xD1
nofXd2 = cndf xD1
}}}
Regardless, we don't know why CSE is not catching this any more, and we
plan to look into it.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5954#comment:4>
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