#5615: ghc produces poor code for `div` with constant powers of 2.
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Reporter: Lennart | Owner: daniel.is.fischer
Type: bug | Status: new
Priority: normal | Milestone: 7.6.1
Component: Compiler | Version: 7.2.1
Keywords: | Os: Unknown/Multiple
Architecture: x86 | Failure: None/Unknown
Difficulty: Unknown | Testcase:
Blockedby: | Blocking:
Related: |
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Comment(by simonpj):
The trouble is that, as you can see above `divInt#` has a pretty big
unfolding, and inlining that at every call site is perhaps overkill. Mind
you, if the denominator is constant, at least some of that unfolding is
dead code. But there's also a test on the numerator too; `quotInt#` is
the primop I think (rightly or wrongly).
I wonder whether this numerator test stuff affects the correctness or
otherwise of replacing `divInt` with a shift?
Anyway, adding a RULE woudl be fine I think.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5615#comment:9>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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