SpecConstr for join points
The attached file Spec.hs
has a case (from Roman's fusion code) where SpecConstr
is not doing the right thing. Let's look at one of the mutually recursive loops that SpecConstr
generates for foo:
lvl_rzY :: GHC.Types.Int
lvl_rzY = GHC.Types.I# 2147483647
lvl1_rA0 :: Data.Either.Either GHC.Types.Int GHC.Types.Int
lvl1_rA0 = Data.Either.Left @ GHC.Types.Int @ GHC.Types.Int lvl_rzY
$s$wgo_szT :: GHC.Prim.Int# -> GHC.Prim.Int# -> GHC.Prim.Int#
$s$wgo_szT =
\ (sc_sz6 :: GHC.Prim.Int#) (sc1_sz7 :: GHC.Prim.Int#) ->
let {
$w$j_syG
:: GHC.Prim.Int#
-> Data.Either.Either GHC.Types.Int GHC.Types.Int
-> GHC.Prim.Int#
[LclId, Arity=2, Str=DmdType LS]
$w$j_syG =
\ (ww_sy6 :: GHC.Prim.Int#)
(w2_sy8 :: Data.Either.Either GHC.Types.Int GHC.Types.Int) ->
case GHC.Prim.<=# ww_sy6 0 of _ {
GHC.Bool.False -> $wgo_syE (GHC.Prim.+# sc_sz6 ww_sy6) w2_sy8;
GHC.Bool.True -> $wgo_syE sc_sz6 w2_sy8
} } in
case GHC.Prim.># sc1_sz7 0 of _ {
GHC.Bool.False -> $s$wgo1_szS sc_sz6 ipv_swo;
GHC.Bool.True ->
case sc1_sz7 of wild1_awb {
__DEFAULT ->
case GHC.Prim.remInt# wild1_awb 2 of _ {
__DEFAULT -> $s$wgo_szT sc_sz6 (GHC.Prim.-# wild1_awb 1);
0 ->
case w1_syr of _ { GHC.Types.I# ww_sy6 ->
$w$j_syG
ww_sy6
(Data.Either.Left
@ GHC.Types.Int
@ GHC.Types.Int
(GHC.Types.I# (GHC.Prim.-# wild1_awb 1)))
}
};
(-2147483648) ->
case w1_syr of _ { GHC.Types.I# ww_sy6 ->
$w$j_syG ww_sy6 lvl1_rA0
}
}
};
Note that the join point has an argument of type (Either Int Int)
but it is always called with (Left (I# <n>))
. This means that the recursive call in the join point is always of the form ($wgo_syE <m> (Left (I# <n>)))
and we have a specialisation for that. However the join point itself doesn't scrutinse its argument, and that means that GHC ignores the potential specialisation.
Simon
Trac metadata
Trac field | Value |
---|---|
Version | 6.12.1 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |