#2132: Optimise nested comparisons
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Reporter: simonpj | Owner: simonpj
Type: bug | Status: patch
Priority: low | Milestone: 7.4.1
Component: Compiler | Version: 6.8.2
Keywords: | Testcase:
Blockedby: | Difficulty: Unknown
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: Runtime performance bug
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Comment(by michalt):
Replying to [comment:17 basvandijk]:
> Would it be hard to extend the language of RULES so that a user can
perform
> this optimization instead of the compiler? ..
Note that this optimization goes a bit further than your example. For
instance, once it knows `x ># y` and `y >=# z` it can optimize away `x <#
z`.
Similarly knowing `x ># 100` and `y <# 10` it can get rid of `x ==# y`.
That would be probably quite difficult to do with rules (even extended).
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2132#comment:18>
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