Repository : http://darcs.haskell.org/ghc.git/
On branch : master https://github.com/ghc/ghc/commit/5949ff2ddb715c3218c2cb96fd7170bae2ee02db >--------------------------------------------------------------- commit 5949ff2ddb715c3218c2cb96fd7170bae2ee02db Author: Simon Peyton Jones <simo...@microsoft.com> Date: Thu May 30 12:22:38 2013 +0100 Refine 'type_determines_value' in Specialise. Fix Trac #7785. See Note [Type determines value] in Specialise. >--------------------------------------------------------------- compiler/specialise/Specialise.lhs | 40 ++++++++++++++++++++++++++++++-------- 1 file changed, 32 insertions(+), 8 deletions(-) diff --git a/compiler/specialise/Specialise.lhs b/compiler/specialise/Specialise.lhs index 212a7fe..a161444 100644 --- a/compiler/specialise/Specialise.lhs +++ b/compiler/specialise/Specialise.lhs @@ -10,7 +10,7 @@ module Specialise ( specProgram ) where import Id import TcType hiding( substTy, extendTvSubstList ) -import Type( TyVar, isDictTy, mkPiTypes ) +import Type( TyVar, isDictTy, mkPiTypes, classifyPredType, PredTree(..), isIPClass ) import Coercion( Coercion ) import CoreMonad import qualified CoreSubst @@ -1597,7 +1597,9 @@ mkCallUDs :: SpecEnv -> Id -> [CoreExpr] -> UsageDetails mkCallUDs env f args | not (want_calls_for f) -- Imported from elsewhere || null theta -- Not overloaded - || not (all type_determines_value theta) + = emptyUDs + + | not (all type_determines_value theta) || not (spec_tys `lengthIs` n_tyvars) || not ( dicts `lengthIs` n_dicts) || not (any (interestingDict env) dicts) -- Note [Interesting dictionary arguments] @@ -1625,14 +1627,36 @@ mkCallUDs env f args want_calls_for f = isLocalId f || isInlinablePragma (idInlinePragma f) - type_determines_value pred = isClassPred pred && not (isIPPred pred) - -- Only specialise if all overloading is on non-IP *class* params, - -- because these are the ones whose *type* determines their *value*. - -- In ptic, with implicit params, the type args - -- *don't* say what the value of the implicit param is! - -- See Trac #7101 + type_determines_value pred -- See Note [Type determines value] + = case classifyPredType pred of + ClassPred cls _ -> not (isIPClass cls) + TuplePred ps -> all type_determines_value ps + EqPred {} -> True + IrredPred {} -> True -- Things like (D []) where D is a + -- Constraint-ranged family; Trac #7785 \end{code} +Note [Type determines value] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Only specialise if all overloading is on non-IP *class* params, +because these are the ones whose *type* determines their *value*. In +parrticular, with implicit params, the type args *don't* say what the +value of the implicit param is! See Trac #7101 + +However, 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 Trac #7785. + Note [Interesting dictionary arguments] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Consider this _______________________________________________ ghc-commits mailing list ghc-commits@haskell.org http://www.haskell.org/mailman/listinfo/ghc-commits
