diff options
Diffstat (limited to 'compiler/GHC/Core/Opt/Specialise.hs')
| -rw-r--r-- | compiler/GHC/Core/Opt/Specialise.hs | 42 |
1 files changed, 11 insertions, 31 deletions
diff --git a/compiler/GHC/Core/Opt/Specialise.hs b/compiler/GHC/Core/Opt/Specialise.hs index f489ac2eff..8e9e35d208 100644 --- a/compiler/GHC/Core/Opt/Specialise.hs +++ b/compiler/GHC/Core/Opt/Specialise.hs @@ -2514,9 +2514,12 @@ mkCallUDs' env f args -- we decide on a case by case basis if we want to specialise -- on this argument; if so, SpecDict, if not UnspecArg mk_spec_arg arg (Anon InvisArg pred) - | type_determines_value (scaledThing pred) - , interestingDict env arg -- Note [Interesting dictionary arguments] + | not (isIPLikePred (scaledThing pred)) + -- See Note [Type determines value] + , interestingDict env arg + -- See Note [Interesting dictionary arguments] = SpecDict arg + | otherwise = UnspecArg mk_spec_arg _ (Anon VisArg _) @@ -2529,41 +2532,18 @@ mkCallUDs' env f args -- in specImports -- Use 'realIdUnfolding' to ignore the loop-breaker flag! - type_determines_value pred -- See Note [Type determines value] - = case classifyPredType pred of - ClassPred cls _ -> not (isIPClass cls) -- Superclasses can't be IPs - EqPred {} -> True - IrredPred {} -> True -- Things like (D []) where D is a - -- Constraint-ranged family; #7785 - ForAllPred {} -> True - -{- -Note [Type determines value] -~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -Only specialise on non-IP *class* params, because these are the ones -whose *type* determines their *value*. In particular, with implicit -params, the type args *don't* say what the value of the implicit param -is! See #7101. +{- Note [Type determines value] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Only specialise on non-impicit-parameter predicates, because these +are the ones whose *type* determines their *value*. In particular, +with implicit params, the type args *don't* say what the value of the +implicit param is! See #7101. So we treat implicit params just like ordinary arguments for the purposes of specialisation. Note that we still want to specialise functions with implicit params if they have *other* dicts which are class params; see #17930. -One apparent additional complexity involves type families. For -example, consider - type family D (v::*->*) :: Constraint - type instance D [] = () - f :: D v => v Char -> Int -If we see a call (f "foo"), we'll pass a "dictionary" - () |> (g :: () ~ D []) -and it's good to specialise f at this dictionary. - -So the question is: can an implicit parameter "hide inside" a -type-family constraint like (D a). Well, no. We don't allow - type instance D Maybe = ?x:Int -Hence the IrredPred case in type_determines_value. See #7785. - Note [Interesting dictionary arguments] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider this |