#5298: Inlined functions aren't fully specialised
---------------------------------+------------------------------------------
Reporter: reinerp | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler
Version: 7.0.3 | Keywords:
Testcase: | Blockedby:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: Runtime performance bug
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When a function is inlined, it can expose other functions as candidates
for specialisation, but GHC doesn't specialise them.
For instance, given the two modules
{{{
module A where
{-# INLINABLE fac #-}
fac :: Num a => a -> a
fac 0 = 1
fac n = n * fac (n-1)
{-# INLINE f #-}
f :: Num a => a -> a
f a = fac a
}}}
{{{
module B where
import A
g :: Int -> Int
g x = f x
}}}
we see that f is inlined, but fac isn't specialised for Ints:
{{{
B.g :: Int -> Int
[GblId,
Arity=1,
Unf=Unf{Src=<vanilla>, TopLvl=True, Arity=1, Value=True,
ConLike=True, Cheap=True, Expandable=True,
Guidance=IF_ARGS [0] 30 0}]
B.g =
\ (x_ary :: Int) ->
A.fac @ Int $fNumInt x_ary
}}}
Removing the INLINE pragma on f doesn't help.
Either of the following changes will cause fac to be specialised:
* adding {-# SPECIALISE f :: Int -> Int #-} to module B
* defining "g x = fac x" instead
This happens with both GHC 7.0.3 and GHC HEAD
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5298>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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