Re: [GHC] #7295: bad code for Double literals
#7295: bad code for Double literals
-+--
Reporter: jwlato| Owner: igloo
Type: bug | Status: patch
Priority: high | Milestone: 7.8.1
Component: Compiler | Version: 7.6.1
Keywords:| Os: Unknown/Multiple
Architecture: Unknown/Multiple | Failure: None/Unknown
Difficulty: Unknown |Testcase:
Blockedby:|Blocking:
Related:|
-+--
Comment(by jwlato@…):
commit 771d376bb6d2ab524741c6d0732718ac2613d2a1
{{{
Author: John Lato jwl...@gmail.com
Date: Mon Oct 8 12:54:55 2012 +0800
add GHC.Float.rationalToFloat, rationalToDouble (fixes #7295)
Adds better support for constant folding of Float/Double literals.
- add rationalToFloat, rationalToDouble with associated Name/Id's in
PrelNames.
- add a matching rule in PrelRules for rationalTo* functions.
compiler/prelude/PrelNames.lhs | 13 +
compiler/prelude/PrelRules.lhs | 29 +
2 files changed, 42 insertions(+), 0 deletions(-)
}}}
--
Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/7295#comment:7
GHC http://www.haskell.org/ghc/
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Re: [GHC] #7295: bad code for Double literals
#7295: bad code for Double literals ---+ Reporter: jwlato| Owner: igloo Type: bug | Status: closed Priority: high | Milestone: 7.8.1 Component: Compiler |Version: 7.6.1 Resolution: fixed | Keywords: Os: Unknown/Multiple | Architecture: Unknown/Multiple Failure: None/Unknown | Difficulty: Unknown Testcase:| Blockedby: Blocking:|Related: ---+ Changes (by igloo): * status: patch = closed * resolution: = fixed Comment: Thanks for the patches; I've applied them. -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/7295#comment:8 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] #7295: bad code for Double literals
#7295: bad code for Double literals -+-- Reporter: jwlato| Owner: igloo Type: bug | Status: patch Priority: high | Milestone: 7.8.1 Component: Compiler | Version: 7.6.1 Keywords:| Os: Unknown/Multiple Architecture: Unknown/Multiple | Failure: None/Unknown Difficulty: Unknown |Testcase: Blockedby:|Blocking: Related:| -+-- Changes (by conrad): * cc: conrad@… (added) -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/7295#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] #7295: bad code for Double literals
#7295: bad code for Double literals -+-- Reporter: jwlato| Owner: igloo Type: bug | Status: patch Priority: high | Milestone: 7.8.1 Component: Compiler | Version: 7.6.1 Keywords:| Os: Unknown/Multiple Architecture: Unknown/Multiple | Failure: None/Unknown Difficulty: Unknown |Testcase: Blockedby:|Blocking: Related:| -+-- Changes (by erikd): * cc: mle+hs@… (added) -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/7295#comment:5 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] #7295: bad code for Double literals
#7295: bad code for Double literals -+-- Reporter: jwlato| Owner: igloo Type: bug | Status: patch Priority: high | Milestone: 7.8.1 Component: Compiler | Version: 7.6.1 Keywords:| Os: Unknown/Multiple Architecture: Unknown/Multiple | Failure: None/Unknown Difficulty: Unknown |Testcase: Blockedby:|Blocking: Related:| -+-- Comment(by simonpj): Thanks! That's part of it, but you need a corresponding change to the library or nothing will happen. Ian owns the ticket now, and your work will make it easier. -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/7295#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] #7295: bad code for Double literals
#7295: bad code for Double literals -+-- Reporter: jwlato| Owner: igloo Type: bug | Status: patch Priority: high | Milestone: 7.8.1 Component: Compiler | Version: 7.6.1 Keywords:| Os: Unknown/Multiple Architecture: Unknown/Multiple | Failure: None/Unknown Difficulty: Unknown |Testcase: Blockedby:|Blocking: Related:| -+-- Changes (by jwlato): * status: new = patch Comment: I put together a patch along the lines of SPJ's suggestion. It seems to work for this small test and some other code, but I was unable to validate it (the validation build doesn't work for me with or without this patch). -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/7295#comment:3 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] #7295: bad code for Double literals
#7295: bad code for Double literals
-+--
Reporter: jwlato| Owner: igloo
Type: bug | Status: new
Priority: normal| Milestone:
Component: Compiler | Version: 7.6.1
Keywords:| Os: Unknown/Multiple
Architecture: Unknown/Multiple | Failure: None/Unknown
Difficulty: Unknown |Testcase:
Blockedby:|Blocking:
Related:|
-+--
Changes (by simonpj):
* owner: = igloo
* difficulty: = Unknown
Comment:
Good point. Here's what is happening.
* In `map (* (-0.5)) xs :: [Double]`, the typechecker and/or desugarer
can see a totally mono-typed use of the literal `0.5` at `Double` and so
genreates exactly that literal.
* But in your main example, you define a polymorphic function `f`, whose
type is
{{{
f :: Fractional a = a - a
}}}
Sure, `f` has only one call site but the typechecker/desugarer don't know
that, so they generate `fromRational d (negate d (1 % 2))`, where `d` is
the fractional dictionary.
So, good as the typechecker/desugarer short-cut is for literals, your
example points out that we should do better constant folding for literals
that start life overloaded, but become specialised. This will also happen
when we have a top-level overloaded function that gets specialised.
My solution. In `GHC.Float` we see
{{{
instance Fractional Float where
fromRational = blah blah blah
}}}
Instead we want
{{{
instance Fractioal Float where
{-# INLINE fromRational #-}
fromRational (a :% b) = rationalToFloat a b
rationalToFloat :: Integer - Integer - Float
{-# NOINLINE [1] rationalToFloat
rationalToFloat = blah blah blah -- As before
}}}
AND we want a constant-folding rule in `PrelRules` for `rationalToFloat`
that spots two `Integer`-literal arguments and produces the right float;
just like `TcHsSyn.shortCutLit` does.
Same for `fromRational` at `Double`.
We already have similar mechanisms for `fromInteger`, so I think that's
all right.
Simon
--
Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/7295#comment:1
GHC http://www.haskell.org/ghc/
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Re: [GHC] #7295: bad code for Double literals
#7295: bad code for Double literals -+-- Reporter: jwlato| Owner: igloo Type: bug | Status: new Priority: high | Milestone: 7.8.1 Component: Compiler | Version: 7.6.1 Keywords:| Os: Unknown/Multiple Architecture: Unknown/Multiple | Failure: None/Unknown Difficulty: Unknown |Testcase: Blockedby:|Blocking: Related:| -+-- Changes (by simonpj): * priority: normal = high * milestone: = 7.8.1 -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/7295#comment:2 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
