#3755: Improve join point inlining
---------------------------------+------------------------------------------
Reporter: simonpj | Owner:
Type: task | Status: new
Priority: normal | Milestone: 7.2.1
Component: Compiler | Version: 6.12.1
Keywords: | Testcase:
Blockedby: | Difficulty:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: Runtime performance bug
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Comment(by reinerp):
I just ran into this when playing around with view patterns, with a
significantly smaller minimial example:
{{{
{-# LANGUAGE ViewPatterns #-}
module Test1 where
data D1 = A | B | C
data D2 = A' | B' | C'
conv A = A'
conv B = B'
conv C = C'
foo :: (b -> D2) -> b -> a -> [a]
foo f (f -> A') a = [a]
foo f (f -> B') a = reverse [a]
foo f (f -> C') a = reverse (reverse [a]) -- put some junk in the RHS to
make it too big to inline
{-# INLINE foo #-}
h :: D1 -> a -> [a]
h a b = foo conv a b
-- "manually inlined" version
j :: D1 -> a -> [a]
j (conv -> A') a = [a]
j (conv -> B') a = reverse [a]
j (conv -> C') a = reverse (reverse [a])
}}}
With GHC on -O2, we get this core:
{{{
Test1.h =
\ (@ a_ad5) (a_abW :: Test1.D1) (b_abX :: a_ad5) ->
let {
$w$j_sfk :: [a_ad5]
[LclId, Str=DmdType]
$w$j_sfk =
case a_abW of _ {
Test1.A -> Test1.h1 @ a_ad5;
Test1.B ->
GHC.List.reverse1
@ a_ad5
(GHC.Types.: @ a_ad5 b_abX (GHC.Types.[] @ a_ad5))
(GHC.Types.[] @ a_ad5);
Test1.C ->
GHC.List.reverse1
@ a_ad5
(GHC.List.reverse1
@ a_ad5
(GHC.Types.: @ a_ad5 b_abX (GHC.Types.[] @ a_ad5))
(GHC.Types.[] @ a_ad5))
(GHC.Types.[] @ a_ad5)
} } in
case a_abW of _ {
Test1.A -> GHC.Types.: @ a_ad5 b_abX (GHC.Types.[] @ a_ad5);
Test1.B -> $w$j_sfk;
Test1.C -> $w$j_sfk
}
}}}
Interestingly, the "manually inlined" function j has the core we want:
{{{
Test1.j =
\ (@ a_ad7) (ds_ddP :: Test1.D1) (a_abY :: a_ad7) ->
case ds_ddP of _ {
Test1.A -> GHC.Types.: @ a_ad7 a_abY (GHC.Types.[] @ a_ad7);
Test1.B ->
GHC.List.reverse1
@ a_ad7
(GHC.Types.: @ a_ad7 a_abY (GHC.Types.[] @ a_ad7))
(GHC.Types.[] @ a_ad7);
Test1.C ->
GHC.List.reverse1
@ a_ad7
(GHC.List.reverse1
@ a_ad7
(GHC.Types.: @ a_ad7 a_abY (GHC.Types.[] @ a_ad7))
(GHC.Types.[] @ a_ad7))
(GHC.Types.[] @ a_ad7)
}
}}}
Reiner
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/3755#comment:4>
GHC <http://www.haskell.org/ghc/>
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