#4978: Continuation passing style loop doesn't compile into a loop
---------------------------------+------------------------------------------
Reporter: tibbe | Owner:
Type: bug | Status: new
Priority: normal | Milestone: 7.4.1
Component: Compiler | Version: 7.0.1
Keywords: | Testcase:
Blockedby: | Difficulty:
Os: Unknown/Multiple | Blocking:
Architecture: Unknown/Multiple | Failure: None/Unknown
---------------------------------+------------------------------------------
Comment(by tibbe):
The above change to `go_pap` does improve the performance in the binary
package's benchmark suite by a bit, but the core still doesn't look great.
Here's an example from `Repro3.hs`:
{{{
$wa =
\ (w_s11t :: [Word8])
(w1_s11u :: Buffer -> [ByteString])
(ww_s11x :: Addr#)
(ww1_s11y :: ForeignPtrContents)
(ww2_s11z :: Int#)
(ww3_s11A :: Int#)
(ww4_s11B :: Int#) ->
case w_s11t of _ {
[] -> w1_s11u (Buffer ww_s11x ww1_s11y ww2_s11z ww3_s11A ww4_s11B);
: x1_ax1 xs1_ax2 ->
let {
$weta_s11K =
\ (ww5_s11j :: Addr#)
(ww6_s11k :: ForeignPtrContents)
(ww7_s11l :: Int#)
(ww8_s11m :: Int#)
(ww9_s11n :: Int#) ->
case x1_ax1 of _ { W8# x2_aYW ->
case writeWord8OffAddr#
(plusAddr# ww5_s11j (+# ww7_s11l ww8_s11m)) 0 x2_aYW
realWorld#
of s2_aYY { __DEFAULT ->
case touch# ww6_s11k s2_aYY of _ { __DEFAULT ->
$wa
xs1_ax2
w1_s11u
ww5_s11j
ww6_s11k
ww7_s11l
(+# ww8_s11m 1)
(-# ww9_s11n 1)
}
}
} } in
case <=# 1 ww4_s11B of _ {
False ->
case ww3_s11A of wild2_X18 {
__DEFAULT ->
: (PS ww_s11x ww1_s11y ww2_s11z wild2_X18)
(case newPinnedByteArray# 32752 realWorld#
of _ { (# _, mbarr#_a10h #) ->
$weta_s11K
(byteArrayContents# (mbarr#_a10h `cast` ...))
(PlainPtr mbarr#_a10h)
0
0
32752
});
0 ->
case newPinnedByteArray# 32752 realWorld#
of _ { (# _, mbarr#_a10h #) ->
$weta_s11K
(byteArrayContents# (mbarr#_a10h `cast` ...))
(PlainPtr mbarr#_a10h)
0
0
32752
}
};
True -> $weta_s11K ww_s11x ww1_s11y ww2_s11z ww3_s11A ww4_s11B
}
}
}}}
It would be better to duplicate `$weta_s11K` in both branches instead of
allocating a closure.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4978#comment:14>
GHC <http://www.haskell.org/ghc/>
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