diff options
Diffstat (limited to 'compiler/specialise')
| -rw-r--r-- | compiler/specialise/SpecConstr.lhs | 22 |
1 files changed, 20 insertions, 2 deletions
diff --git a/compiler/specialise/SpecConstr.lhs b/compiler/specialise/SpecConstr.lhs index f126bdac47..99f1c79f44 100644 --- a/compiler/specialise/SpecConstr.lhs +++ b/compiler/specialise/SpecConstr.lhs @@ -1489,6 +1489,19 @@ The function calcSpecStrictness performs the calculation. This code deals with analysing call-site arguments to see whether they are constructor applications. +Note [Free type variables of the qvar types] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +In a call (f @a x True), that we want to specialise, what varaibles should +we quantify over. Clearly over 'a' and 'x', but what about any type variables +free in x's type? In fact we don't need to worry about them because (f @a) +can only be a well-typed application if its type is compatible with x, so any +varaibles free in x's type must be free in (f @a), and hence either be gathered +via 'a' itself, or be in scope at f's defn. Hence we just take + (exprsFreeVars pats). + +BUT phantom type synonums can mess this reasoning up, + eg x::T b with type T b = Int +So we apply expandTypeSynonyms to the bound Ids. Yuk. \begin{code} type CallPat = ([Var], [CoreExpr]) -- Quantified variables and arguments @@ -1520,16 +1533,21 @@ callToPats env bndr_occs (con_env, args) = do { let in_scope = substInScope (sc_subst env) ; (interesting, pats) <- argsToPats env in_scope con_env args bndr_occs ; let pat_fvs = varSetElems (exprsFreeVars pats) - qvars = filterOut (`elemInScopeSet` in_scope) pat_fvs + in_scope_vars = getInScopeVars in_scope + qvars = filterOut (`elemVarSet` in_scope_vars) pat_fvs -- Quantify over variables that are not in sccpe -- at the call site + -- See Note [Free type variables of the qvar types] -- See Note [Shadowing] at the top (tvs, ids) = partition isTyVar qvars - qvars' = tvs ++ ids + qvars' = tvs ++ map sanitise ids -- Put the type variables first; the type of a term -- variable may mention a type variable + sanitise id = id `setIdType` expandTypeSynonyms (idType id) + -- See Note [Free type variables of the qvar types] + ; -- pprTrace "callToPats" (ppr args $$ ppr prs $$ ppr bndr_occs) $ if interesting then return (Just (qvars', pats)) |