#4081: Strict constructor fields inspected in loop
---------------------------------+------------------------------------------
Reporter: rl | Owner:
Type: bug | Status: new
Priority: normal | Milestone: 7.0.2
Component: Compiler | Version: 6.13
Keywords: | Testcase:
Blockedby: | Difficulty:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: Runtime performance bug
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Comment(by simonpj):
I'm pretty certain we can fix this. My plan is simply to extend the let-
floater to float out `(case x of I# y -> ...)`, where x is known to be
evaluated. (Of course, for any product type, not just Int.)
How might x be known to be evaluated? The usual way is by an enclosing
'case', but that won't happen here because the inner case would simply
vanish. No, it'll be because you pattern match on a strict constructor
{{{
case v of
C x -> ....(case x of I# y -> ...) ...
}}}
where
{{{
data C a = C !a
}}}
I believe that these strict constructors are the cases you are concerned
about, correct?
Simon
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4081#comment:7>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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