#1885: Improve CPR analysis
--+-
Reporter: simonpj | Owner: simonpj
Type: task | Status: new
Priority: normal| Milestone: 6.10 branch
Component: Compiler |Version: 6.8.1
Severity: normal| Resolution:
Keywords:| Difficulty: Unknown
Testcase:| Architecture: Unknown
Os: Unknown |
--+-
Old description:
When a function returns a ''nested'' data structure, GHC should expose
that fact to the caller. This can make a very big difference in inner
loops. A good example is the following message (from GHC users).
Compile the attached files thus:
{{{
ghc --make Unpacked.hs -O2 -cpp -DPOLY_SAME
}}}
and similarly with `DPOLY_OTHER`. The `POLY_OTHER` case does a lot more
allocation because a key function isn't inlined.
{{{
$wa_r1Wb :: GHC.Prim.Addr#
- GHC.Prim.State# GHC.Prim.RealWorld
- (# GHC.Prim.State# GHC.Prim.RealWorld,
OtherP.C
GHC.Float.Double (OtherP.C GHC.Float.Double
(OtherP.C GHC.Float.Double ()))
#)
[GlobalId]
[Arity 2
NoCafRefs
Str: DmdType LL]
$wa_r1Wb =
\ (ww_s1S5 :: GHC.Prim.Addr#) (w_s1S7 :: GHC.Prim.State#
GHC.Prim.RealWorld) -
case GHC.Prim.readDoubleOffAddr# @ GHC.Prim.RealWorld ww_s1S5 0
w_s1S7
of wild2_a1xI { (# s2_a1xK, x_a1xL #) -
let {
ipv_XGd [Just L] :: GHC.Prim.Addr#
[Str: DmdType]
ipv_XGd = GHC.Prim.plusAddr# ww_s1S5 8 } in
case GHC.Prim.readDoubleOffAddr# @ GHC.Prim.RealWorld ipv_XGd 0
s2_a1xK
of wild21_X1yK { (# s21_X1yN, x1_X1yP #) -
case GHC.Prim.readDoubleOffAddr#
@ GHC.Prim.RealWorld (GHC.Prim.plusAddr# ipv_XGd 8) 0 s21_X1yN
of wild22_X1yU { (# s22_X1yX, x2_X1yZ #) -
(# s22_X1yX,
OtherP.C
@ GHC.Float.Double
@ (OtherP.C GHC.Float.Double (OtherP.C GHC.Float.Double ()))
(GHC.Float.D# x_a1xL)
(OtherP.C
@ GHC.Float.Double
@ (OtherP.C GHC.Float.Double ())
(GHC.Float.D# x1_X1yP)
(OtherP.C @ GHC.Float.Double @ ()
(GHC.Float.D# x2_X1yZ) GHC.Base.())) #)
} } }
}}}
New description:
When a function returns a ''nested'' data structure, GHC should expose
that fact to the caller. This can make a very big difference in inner
loops. A good example is the following message (from GHC users
http://www.haskell.org/pipermail/glasgow-haskell-
users/2007-November/013454.html).
Compile the attached files thus:
{{{
ghc --make Unpacked.hs -O2 -cpp -DPOLY_SAME
}}}
and similarly with `DPOLY_OTHER`. The `POLY_OTHER` case does a lot more
allocation because a key function isn't inlined.
{{{
$wa_r1Wb :: GHC.Prim.Addr#
- GHC.Prim.State# GHC.Prim.RealWorld
- (# GHC.Prim.State# GHC.Prim.RealWorld,
OtherP.C
GHC.Float.Double (OtherP.C GHC.Float.Double
(OtherP.C GHC.Float.Double ()))
#)
[GlobalId]
[Arity 2
NoCafRefs
Str: DmdType LL]
$wa_r1Wb =
\ (ww_s1S5 :: GHC.Prim.Addr#) (w_s1S7 :: GHC.Prim.State#
GHC.Prim.RealWorld) -
case GHC.Prim.readDoubleOffAddr# @ GHC.Prim.RealWorld ww_s1S5 0 w_s1S7
of wild2_a1xI { (# s2_a1xK, x_a1xL #) -
let {
ipv_XGd [Just L] :: GHC.Prim.Addr#
[Str: DmdType]
ipv_XGd = GHC.Prim.plusAddr# ww_s1S5 8 } in
case GHC.Prim.readDoubleOffAddr# @ GHC.Prim.RealWorld ipv_XGd 0
s2_a1xK
of wild21_X1yK { (# s21_X1yN, x1_X1yP #) -
case GHC.Prim.readDoubleOffAddr#
@ GHC.Prim.RealWorld (GHC.Prim.plusAddr# ipv_XGd 8) 0 s21_X1yN
of wild22_X1yU { (# s22_X1yX, x2_X1yZ #) -
(# s22_X1yX,
OtherP.C
@ GHC.Float.Double
@ (OtherP.C GHC.Float.Double (OtherP.C GHC.Float.Double ()))
(GHC.Float.D# x_a1xL)
(OtherP.C
@ GHC.Float.Double
@ (OtherP.C GHC.Float.Double ())
(GHC.Float.D# x1_X1yP)
(OtherP.C @ GHC.Float.Double @ ()
(GHC.Float.D# x2_X1yZ) GHC.Base.())) #)
} } }
}}}
--
Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/1885#comment:1
GHC http://www.haskell.org/ghc/
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