#15445: SPCIALIZE one of two identical functions does not fire well
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Reporter: nobrakal | Owner: (none)
Type: bug | Status: new
Priority: normal | Milestone: 8.6.1
Component: Compiler | Version: 8.4.3
Keywords: | Operating System: Linux
Architecture: x86_64 (amd64) | Type of failure: None/Unknown
Test Case: | Blocked By:
Blocking: | Related Tickets:
Differential Rev(s): | Wiki Page:
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Hi,
I am playing with `SPECIALIZE` pragma:
{{{#!hs
module Todo where
{-# SPECIALIZE plusTwoRec :: [Int] -> [Int] #-}
plusTwoRec :: Num a => [a] -> [a]
plusTwoRec [] = []
plusTwoRec (x:xs) = x+2:plusTwoRec xs
plusTwoRec' :: Num a => [a] -> [a]
plusTwoRec' [] = []
plusTwoRec' (x:xs) = x+2:plusTwoRec' xs
}}}
And wanted to benchmark it with (in `Main.hs`):
{{{#!hs
import Todo
import Criterion.Main
aListOfInt :: [Int]
aListOfInt = [1..10000]
main :: IO ()
main = defaultMain
[ bench "plusTwoRec" $ nf plusTwoRec aListOfInt
, bench "plusTwoRec'" $ nf plusTwoRec' aListOfInt
]
}}}
Sadly, the rule of specialization of `plusTwoRec` does not fire in Main.hs
(I compiled with:
`ghc Main.hs -O -dynamic -ddump-rule-firings` (the `-dynamic` part is due
to my ArchLinux installaltion)).
The result is:
{{{
[1 of 2] Compiling Todo ( Todo.hs, Todo.o )
Rule fired: Class op + (BUILTIN)
Rule fired: Class op fromInteger (BUILTIN)
Rule fired: integerToInt (BUILTIN)
Rule fired: SPEC plusTwoRec (Todo)
[2 of 2] Compiling Main ( Main.hs, Main.o )
Rule fired: Class op enumFromTo (BUILTIN)
Rule fired: unpack (GHC.Base)
Rule fired: unpack (GHC.Base)
Rule fired: eftIntList (GHC.Enum)
Rule fired: unpack-list (GHC.Base)
Rule fired: unpack-list (GHC.Base)
Linking Main ...
}}}
I have inspected a bit the code produced after the simplifications passes
(with `-ddump-simpl`) and here is the suspicious part:
{{{
plusTwoRec :: forall a. Num a => [a] -> [a]
[GblId,
Arity=2,
Caf=NoCafRefs,
Str=