Commit 44674ca1 authored by dimitris@microsoft.com's avatar dimitris@microsoft.com
Browse files

Midstream changes for performance improvement related to superclasses and functional dependencies.

parent 2207ce8c
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......@@ -4,7 +4,7 @@ module TcSMonad (
-- Canonical constraints
CanonicalCts, emptyCCan, andCCan, andCCans,
singleCCan, extendCCans, isEmptyCCan,
singleCCan, extendCCans, isEmptyCCan, isEqCCan,
CanonicalCt(..), Xi, tyVarsOfCanonical, tyVarsOfCanonicals,
mkWantedConstraints, deCanonicaliseWanted,
makeGivens, makeSolved,
......@@ -254,6 +254,12 @@ emptyCCan = emptyBag
isEmptyCCan :: CanonicalCts -> Bool
isEmptyCCan = isEmptyBag
isEqCCan :: CanonicalCt -> Bool
isEqCCan (CTyEqCan {}) = True
isEqCCan (CFunEqCan {}) = True
isEqCCan _ = False
\end{code}
%************************************************************************
......@@ -307,35 +313,7 @@ canSolve _ _ = False
canRewrite :: CtFlavor -> CtFlavor -> Bool
-- canRewrite ctid1 ctid2
-- The *equality_constraint* ctid1 can be used to rewrite inside ctid2
canRewrite (Given {}) _ = True
canRewrite (Derived {}) (Wanted {}) = True
canRewrite (Derived {}) (Derived {}) = True
-- See note [Rewriting wanteds with wanteds]
canRewrite (Wanted {}) (Wanted {}) = False
canRewrite _ _ = False
\end{code}
Note [Rewriting wanteds with wanteds]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We will currently never use a wanted to rewrite any other
constraint (function @canRewrite@). If a rewriting was possible at all,
we simply wait until the wanted equality becomes given or derived and
then use it. This way we avoid rewriting by eventually insoluble wanteds,
such as in the following situation:
w1 : a ~ Int
w2 : F a ~ a
w3 : F Int ~ G Bool
where 'a' is a skolem variable. If we rewrite using w1 inside w2 we will
get the perhaps mystifying error at the end that we could not solve
(a ~ Int) and (G Bool ~ Int). But there is no point in rewriting with
a ~ Int as long as it is still wanted.
Notice that on the other hand we often do solve one wanted from another,
(function @canSolve@) for instance in dictionary interactions, which is
a reaction that enables sharing both in the solver and in the final evidence
produced.
\begin{code}
canRewrite = canSolve
combineCtLoc :: CtFlavor -> CtFlavor -> WantedLoc
-- Precondition: At least one of them should be wanted
......
......@@ -18,6 +18,8 @@ import TcInteract
import Inst
import Var
import VarSet
import VarEnv ( varEnvElts )
import Name
import NameEnv ( emptyNameEnv )
import Bag
......@@ -629,10 +631,13 @@ solveWanteds inert wanteds
, text "inert =" <+> ppr inert ]
; (unsolved_flats, unsolved_implics)
<- simpl_loop 1 can_flats implic_wanteds
; bb <- getTcEvBindsBag
; traceTcS "solveWanteds }" $
vcat [ text "wanteds =" <+> ppr wanteds
, text "unsolved_flats =" <+> ppr unsolved_flats
, text "unsolved_implics =" <+> ppr unsolved_implics ]
, text "unsolved_implics =" <+> ppr unsolved_implics
, text "current evbinds =" <+> vcat (map ppr (varEnvElts bb))
]
; return (unsolved_flats, unsolved_implics) }
where
simpl_loop :: Int
......
......@@ -207,9 +207,10 @@ improveFromInstEnv :: (Class -> [Instance])
improveFromInstEnv _inst_env pred
= improveOne _inst_env pred [] -- TODO: Refactor to directly use instance_eqnd?
improveFromAnother :: Pred_Loc
improveFromAnother :: Pred_Loc
-> Pred_Loc
-> [(Equation,Pred_Loc,Pred_Loc)]
-> [(Equation, Pred_Loc, Pred_Loc)]
-- Improvement from another local (given or wanted) constraint
improveFromAnother pred1 pred2
= improveOne (\_ -> []) pred1 [pred2] -- TODO: Refactor to directly use pairwise_eqns?
......
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