Re: [GHC] #3744: Comparisons against minBound/maxBound not optimised
#3744: Comparisons against minBound/maxBound not optimised --+- Reporter: rl | Owner: Type: bug | Status: closed Priority: normal | Milestone: 7.2.1 Component: Compiler |Version: 6.13 Resolution: fixed| Keywords: Testcase: | Blockedby: Difficulty: | Os: Unknown/Multiple Blocking: | Architecture: Unknown/Multiple Failure: Runtime performance bug | --+- Comment(by michalt): Replying to [comment:10 simonpj]: The optimisation seems ok, but does this situation ever arise in practice? Who asks `x minBound`? Simon Well, I'm pretty sure I've never wrote something like that. ;) On the other hand the ticket has been around for a while with a comment or two, so I thought that the optimization might be useful for someone. But I don't really feel strongly about it. -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/3744#comment:11 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler ___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
Re: [GHC] #3744: Comparisons against minBound/maxBound not optimised
#3744: Comparisons against minBound/maxBound not optimised
--+-
Reporter: rl | Owner:
Type: bug | Status: new
Priority: normal | Milestone: 7.2.1
Component: Compiler |Version: 6.13
Resolution: | Keywords:
Testcase: | Blockedby:
Difficulty: | Os: Unknown/Multiple
Blocking: | Architecture: Unknown/Multiple
Failure: Runtime performance bug |
--+-
Changes (by rl):
* status: closed = new
* resolution: fixed =
Comment:
Replying to [comment:10 simonpj]:
The optimisation seems ok, but does this situation ever arise in
practice? Who asks `x minBound`?
Me! I jump through some hoops in vector to avoid the following problem.
{{{
foo :: Num a = a - a
{-# INLINE foo #-}
foo x | x 0 = error Negative argument
| otherwise = e
bar :: Word - Word
bar x = foo x + 1
}}}
I completely missed the patch, thanks a lot for this! Unfortunately, it
doesn't handle Int8/Int16/Word8/Word16 and Int32/Word32 on 64 bit systems.
It isn't very clear how to do this because we only have Int# and Word# in
Core. Also, the inlining of minBound/maxBound for 64 bit types on 32 bit
systems which this patch depends on doesn't work reliably. So this ticket
isn't quite fixed yet but this is good progress!
--
Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/3744#comment:12
GHC http://www.haskell.org/ghc/
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Re: [GHC] #3744: Comparisons against minBound/maxBound not optimised
#3744: Comparisons against minBound/maxBound not optimised --+- Reporter: rl | Owner: Type: bug | Status: closed Priority: normal | Milestone: 7.2.1 Component: Compiler |Version: 6.13 Resolution: fixed| Keywords: Testcase: | Blockedby: Difficulty: | Os: Unknown/Multiple Blocking: | Architecture: Unknown/Multiple Failure: Runtime performance bug | --+- Changes (by igloo): * status: patch = closed * resolution: = fixed Comment: Sorry for the delay. Now applied, thanks. -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/3744#comment:9 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler ___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
Re: [GHC] #3744: Comparisons against minBound/maxBound not optimised
#3744: Comparisons against minBound/maxBound not optimised --+- Reporter: rl | Owner: Type: bug | Status: closed Priority: normal | Milestone: 7.2.1 Component: Compiler |Version: 6.13 Resolution: fixed| Keywords: Testcase: | Blockedby: Difficulty: | Os: Unknown/Multiple Blocking: | Architecture: Unknown/Multiple Failure: Runtime performance bug | --+- Comment(by simonpj): The optimisation seems ok, but does this situation ever arise in practice? Who asks `x minBound`? Simon -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/3744#comment:10 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler ___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
Re: [GHC] #3744: Comparisons against minBound/maxBound not optimised
#3744: Comparisons against minBound/maxBound not optimised
-+--
Reporter: rl|Owner:
Type: bug | Status: new
Priority: normal|Milestone: 7.0.1
Component: Compiler | Version: 6.13
Keywords:| Testcase:
Blockedby:| Difficulty:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: Runtime performance bug
-+--
Changes (by michalt):
* cc: michal.terep...@… (added)
Comment:
I've created a patch with rules for PrelRules.lhs that detect comparisons
with
minBound and maxBound that are always true or always false (like in the
above
examples). And it seems to work just fine:
{{{
foo1, foo2, foo3, foo4 :: Int - Bool
foo1 n = n minBound
foo2 n = n maxBound
foo3 n = n = minBound
foo4 n = n = maxBound
}}}
gives now
{{{
Test.foo1 =
\ (n_aaD :: GHC.Types.Int) -
case n_aaD of _ { GHC.Types.I# _ - GHC.Bool.False }
Test.foo2 =
\ (n_ag0 :: GHC.Types.Int) -
case n_ag0 of _ { GHC.Types.I# _ - GHC.Bool.False }
Test.foo3 =
\ (n_ag1 :: GHC.Types.Int) -
case n_ag1 of _ { GHC.Types.I# _ - GHC.Bool.True }
Test.foo4 =
\ (n_ag2 :: GHC.Types.Int) -
case n_ag2 of _ { GHC.Types.I# _ - GHC.Bool.True }
}}}
This works fine also for Char, and Word, but interestingly in case of
Int64 only
maxBound is inlined, but not minBound (and so foo2 and foo4 are optimised
but
not foo1 and foo3), whereas in case of Word64 the opposite happens. For
example
by changing the type to Int64 in the above code we have:
{{{
Test.foo1 =
\ (n_aaF :: GHC.Int.Int64) -
case n_aaF of _ { GHC.Int.I64# a1_ar3 -
case GHC.Int.$fBoundedInt64_$cminBound
of _ { GHC.Int.I64# b1_ar7 -
GHC.Prim.# a1_ar3 b1_ar7
}
}
Test.foo2 =
\ (n_ag2 :: GHC.Int.Int64) -
case n_ag2 of _ { GHC.Int.I64# _ - GHC.Bool.False }
Test.foo3 =
\ (n_ag3 :: GHC.Int.Int64) -
case n_ag3 of _ { GHC.Int.I64# a1_arn -
case GHC.Int.$fBoundedInt64_$cminBound
of _ { GHC.Int.I64# b1_arr -
GHC.Prim.=# a1_arn b1_arr
}
}
Test.foo4 =
\ (n_ag4 :: GHC.Int.Int64) -
case n_ag4 of _ { GHC.Int.I64# _ - GHC.Bool.True }
}}}
Anyway, I'll attach the patch in a second. And please let me know what do
you
think about it (especially since I don't really know a lot about GHC
internals).
--
Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/3744#comment:5
GHC http://www.haskell.org/ghc/
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Re: [GHC] #3744: Comparisons against minBound/maxBound not optimised
#3744: Comparisons against minBound/maxBound not optimised -+-- Reporter: rl|Owner: Type: bug | Status: patch Priority: normal|Milestone: 7.0.1 Component: Compiler | Version: 6.13 Keywords:| Testcase: Blockedby:| Difficulty: Os: Unknown/Multiple | Blocking: Architecture: Unknown/Multiple | Failure: Runtime performance bug -+-- Changes (by michalt): * status: new = patch -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/3744#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler ___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
Re: [GHC] #3744: Comparisons against minBound/maxBound not optimised
#3744: Comparisons against minBound/maxBound not optimised
-+--
Reporter: rl|Owner:
Type: bug | Status: new
Priority: normal|Milestone: 7.0.1
Component: Compiler | Version: 6.13
Keywords:| Testcase:
Blockedby:| Difficulty:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: Runtime performance bug
-+--
Changes (by daniel.is.fischer):
* cc: daniel.is.fisc...@… (added)
Comment:
A global
{{{
{-# RULES
()/minBound forall x. x minBound = False
()/minBound forall x. minBound x = False
etc.
#-}
}}}
would eliminate those checks in many (almost all, hopefully) cases.
However, it would break user code relying on incompatible Ord and Enum
instances (it should not break local bindings for minBound/maxBound since
the rule refers to GHC.Enum.minBound).
Alternatively, one could add those rules for every pertinent type, but I'd
prefer a more general solution.
--
Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/3744#comment:3
GHC http://www.haskell.org/ghc/
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Re: [GHC] #3744: Comparisons against minBound/maxBound not optimised
#3744: Comparisons against minBound/maxBound not optimised -+-- Reporter: rl|Owner: Type: bug | Status: new Priority: normal|Milestone: 7.0.1 Component: Compiler | Version: 6.13 Keywords:| Testcase: Blockedby:| Difficulty: Os: Unknown/Multiple | Blocking: Architecture: Unknown/Multiple | Failure: Runtime performance bug -+-- Comment(by rl): I don't think these rules would work reliably because the comparison operators could (and would) be inlined before the rules have had a chance to fire. Rules for specific primitive types wouldn't have this problem but IIRC, matching against the actual bounds literals can be problematic. -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/3744#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler ___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
Re: [GHC] #3744: Comparisons against minBound/maxBound not optimised
#3744: Comparisons against minBound/maxBound not optimised -+-- Reporter: rl|Owner: Type: bug | Status: new Priority: normal|Milestone: 6.14 branch Component: Compiler | Version: 6.13 Keywords:| Difficulty: Os: Unknown/Multiple | Testcase: Architecture: Unknown/Multiple | Failure: Runtime performance bug -+-- Changes (by igloo): * milestone: = 6.14 branch -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/3744#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler ___ Glasgow-haskell-bugs mailing list Glasgow-haskell-bugs@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
