addIdSpecialisations,
-- * Misc. CoreRule helpers
- rulesOfBinds, getRules, pprRulesForUser,
+ rulesOfBinds, getRules, pprRulesForUser,
- lookupRule, mkLocalRule, roughTopNames
+ lookupRule, mkRule, mkLocalRule, roughTopNames
) where
#include "HsVersions.h"
import CoreSyn -- All of it
import OccurAnal ( occurAnalyseExpr )
import CoreFVs ( exprFreeVars, exprsFreeVars, bindFreeVars, rulesFreeVars )
-import CoreUtils ( tcEqExprX, exprType )
+import CoreUtils ( exprType, eqExprX )
import PprCore ( pprRules )
import Type ( Type, TvSubstEnv )
import TcType ( tcSplitTyConApp_maybe )
import Name ( Name, NamedThing(..) )
import NameEnv
import Unify ( ruleMatchTyX, MatchEnv(..) )
-import BasicTypes ( Activation )
+import BasicTypes ( Activation, CompilerPhase, isActive )
import StaticFlags ( opt_PprStyle_Debug )
import Outputable
import FastString
\end{code}
+Note [Overall plumbing for rules]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+* The ModGuts initially contains mg_rules :: [CoreRule] of rules
+ declared in this module. During the core-to-core pipeline,
+ locally-declared rules for locally-declared Ids are attached to the
+ IdInfo for that Id, so the mg_rules field of ModGuts now only
+ contains locally-declared rules for *imported* Ids. TidyPgm restores
+ the original setup, so that the ModGuts again has *all* the
+ locally-declared rules. See Note [Attach rules to local ids] in
+ SimplCore
+
+* The HomePackageTable contains a ModDetails for each home package
+ module. Each contains md_rules :: [CoreRule] of rules declared in
+ that module. The HomePackageTable grows as ghc --make does its
+ up-sweep. In batch mode (ghc -c), the HPT is empty; all imported modules
+ are treated by the "external" route, discussed next, regardless of
+ which package they come from.
+
+* The ExternalPackageState has a single eps_rule_base :: RuleBase for
+ Ids in other packages. This RuleBase simply grow monotonically, as
+ ghc --make compiles one module after another.
+
+ During simplification, interface files may get demand-loaded,
+ as the simplifier explores the unfoldings for Ids it has in
+ its hand. (Via an unsafePerformIO; the EPS is really a cache.)
+ That in turn may make the EPS rule-base grow. In contrast, the
+ HPT never grows in this way.
+
+* The result of all this is that during Core-to-Core optimisation
+ there are four sources of rules:
+
+ (a) Rules in the IdInfo of the Id they are a rule for. These are
+ easy: fast to look up, and if you apply a substitution then
+ it'll be applied to the IdInfo as a matter of course.
+
+ (b) Rules declared in this module for imported Ids, kept in the
+ ModGuts. If you do a substitution, you'd better apply the
+ substitution to these. There are seldom many of these.
+
+ (c) Rules declared in the HomePackageTable. These never change.
+
+ (d) Rules in the ExternalPackageTable. These can grow in response
+ to lazy demand-loading of interfaces.
+
+* At the moment (c) is carried in a reader-monad way by the CoreMonad.
+ The HomePackageTable doesn't have a single RuleBase because technically
+ we should only be able to "see" rules "below" this module; so we
+ generate a RuleBase for (c) by combing rules from all the modules
+ "below" us. That's whye we can't just select the home-package RuleBase
+ from HscEnv.
+
+ [NB: we are inconsistent here. We should do the same for external
+ pacakges, but we don't. Same for type-class instances.]
+
+* So in the outer simplifier loop, we combine (b-d) into a single
+ RuleBase, reading
+ (b) from the ModGuts,
+ (c) from the CoreMonad, and
+ (d) from its mutable variable
+ [Of coures this means that we won't see new EPS rules that come in
+ during a single simplifier iteration, but that probably does not
+ matter.]
+
+
%************************************************************************
%* *
\subsection[specialisation-IdInfo]{Specialisation info about an @Id@}
-> Name -> [CoreBndr] -> [CoreExpr] -> CoreExpr -> CoreRule
-- ^ Used to make 'CoreRule' for an 'Id' defined in the module being
-- compiled. See also 'CoreSyn.CoreRule'
-mkLocalRule name act fn bndrs args rhs
+mkLocalRule = mkRule True
+
+mkRule :: Bool -> RuleName -> Activation
+ -> Name -> [CoreBndr] -> [CoreExpr] -> CoreExpr -> CoreRule
+-- ^ Used to make 'CoreRule' for an 'Id' defined in the module being
+-- compiled. See also 'CoreSyn.CoreRule'
+mkRule is_local name act fn bndrs args rhs
= Rule { ru_name = name, ru_fn = fn, ru_act = act,
ru_bndrs = bndrs, ru_args = args,
- ru_rhs = rhs, ru_rough = roughTopNames args,
- ru_local = True }
+ ru_rhs = occurAnalyseExpr rhs,
+ ru_rough = roughTopNames args,
+ ru_local = is_local }
--------------
roughTopNames :: [CoreExpr] -> [Maybe Name]
rulesOfBinds binds = concatMap (concatMap idCoreRules . bindersOf) binds
getRules :: RuleBase -> Id -> [CoreRule]
- -- The rules for an Id come from two places:
- -- (a) the ones it is born with (idCoreRules fn)
- -- (b) rules added in subsequent modules (extra_rules)
- -- PrimOps, for example, are born with a bunch of rules under (a)
+-- See Note [Where rules are found]
getRules rule_base fn
- | isLocalId fn = idCoreRules fn
- | otherwise = WARN( not (isPrimOpId fn) && notNull (idCoreRules fn),
- ppr fn <+> ppr (idCoreRules fn) )
- idCoreRules fn ++ (lookupNameEnv rule_base (idName fn) `orElse` [])
- -- Only PrimOpIds have rules inside themselves, and perhaps more besides
+ = idCoreRules fn ++ imp_rules
+ where
+ imp_rules = lookupNameEnv rule_base (idName fn) `orElse` []
\end{code}
+Note [Where rules are found]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The rules for an Id come from two places:
+ (a) the ones it is born with, stored inside the Id iself (idCoreRules fn),
+ (b) rules added in other modules, stored in the global RuleBase (imp_rules)
+
+It's tempting to think that
+ - LocalIds have only (a)
+ - non-LocalIds have only (b)
+
+but that isn't quite right:
+
+ - PrimOps and ClassOps are born with a bunch of rules inside the Id,
+ even when they are imported
+
+ - The rules in PrelRules.builtinRules should be active even
+ in the module defining the Id (when it's a LocalId), but
+ the rules are kept in the global RuleBase
+
%************************************************************************
%* *
-- supplied rules to this instance of an application in a given
-- context, returning the rule applied and the resulting expression if
-- successful.
-lookupRule :: (Activation -> Bool) -> InScopeSet
+lookupRule :: (Activation -> Bool) -- When rule is active
+ -> IdUnfoldingFun -- When Id can be unfolded
+ -> InScopeSet
-> Id -> [CoreExpr]
-> [CoreRule] -> Maybe (CoreRule, CoreExpr)
-- See Note [Extra args in rule matching]
-- See comments on matchRule
-lookupRule is_active in_scope fn args rules
+lookupRule is_active id_unf in_scope fn args rules
= -- pprTrace "matchRules" (ppr fn <+> ppr rules) $
case go [] rules of
[] -> Nothing
go :: [(CoreRule,CoreExpr)] -> [CoreRule] -> [(CoreRule,CoreExpr)]
go ms [] = ms
- go ms (r:rs) = case (matchRule is_active in_scope args rough_args r) of
+ go ms (r:rs) = case (matchRule is_active id_unf in_scope args rough_args r) of
Just e -> go ((r,e):ms) rs
Nothing -> -- pprTrace "match failed" (ppr r $$ ppr args $$
-- ppr [(arg_id, unfoldingTemplate unf) | Var arg_id <- args, let unf = idUnfolding arg_id, isCheapUnfolding unf] )
isMoreSpecific _ (BuiltinRule {}) = False
isMoreSpecific (Rule { ru_bndrs = bndrs1, ru_args = args1 })
(Rule { ru_bndrs = bndrs2, ru_args = args2 })
- = isJust (matchN in_scope bndrs2 args2 args1)
+ = isJust (matchN id_unfolding_fun in_scope bndrs2 args2 args1)
where
+ id_unfolding_fun _ = NoUnfolding -- Don't expand in templates
in_scope = mkInScopeSet (mkVarSet bndrs1)
-- Actually we should probably include the free vars
-- of rule1's args, but I can't be bothered
noBlackList :: Activation -> Bool
noBlackList _ = False -- Nothing is black listed
-matchRule :: (Activation -> Bool) -> InScopeSet
+matchRule :: (Activation -> Bool) -> IdUnfoldingFun
+ -> InScopeSet
-> [CoreExpr] -> [Maybe Name]
-> CoreRule -> Maybe CoreExpr
-- Any 'surplus' arguments in the input are simply put on the end
-- of the output.
-matchRule _is_active _in_scope args _rough_args
+matchRule _is_active id_unf _in_scope args _rough_args
(BuiltinRule { ru_try = match_fn })
- = case match_fn args of
+-- Built-in rules can't be switched off, it seems
+ = case match_fn id_unf args of
Just expr -> Just expr
Nothing -> Nothing
-matchRule is_active in_scope args rough_args
+matchRule is_active id_unf in_scope args rough_args
(Rule { ru_act = act, ru_rough = tpl_tops,
ru_bndrs = tpl_vars, ru_args = tpl_args,
ru_rhs = rhs })
| not (is_active act) = Nothing
| ruleCantMatch tpl_tops rough_args = Nothing
| otherwise
- = case matchN in_scope tpl_vars tpl_args args of
+ = case matchN id_unf in_scope tpl_vars tpl_args args of
Nothing -> Nothing
Just (binds, tpl_vals) -> Just (mkLets binds $
rule_fn `mkApps` tpl_vals)
-- For a given match template and context, find bindings to wrap around
-- the entire result and what should be substituted for each template variable.
-- Fail if there are two few actual arguments from the target to match the template
-matchN :: InScopeSet -- ^ In-scope variables
+matchN :: IdUnfoldingFun
+ -> InScopeSet -- ^ In-scope variables
-> [Var] -- ^ Match template type variables
-> [CoreExpr] -- ^ Match template
-> [CoreExpr] -- ^ Target; can have more elements than the template
-> Maybe ([CoreBind],
[CoreExpr])
-matchN in_scope tmpl_vars tmpl_es target_es
+matchN id_unf in_scope tmpl_vars tmpl_es target_es
= do { (tv_subst, id_subst, binds)
<- go init_menv emptySubstEnv tmpl_es target_es
; return (fromOL binds,
go _ subst [] _ = Just subst
go _ _ _ [] = Nothing -- Fail if too few actual args
- go menv subst (t:ts) (e:es) = do { subst1 <- match menv subst t e
+ go menv subst (t:ts) (e:es) = do { subst1 <- match id_unf menv subst t e
; go menv subst1 ts es }
lookup_tmpl :: TvSubstEnv -> IdSubstEnv -> Var -> CoreExpr
-- SLPJ July 99
-match :: MatchEnv
+match :: IdUnfoldingFun
+ -> MatchEnv
-> SubstEnv
-> CoreExpr -- Template
-> CoreExpr -- Target
-- succeed in matching what looks like the template variable 'a' against 3.
-- The Var case follows closely what happens in Unify.match
-match menv subst (Var v1) e2
- | Just subst <- match_var menv subst v1 e2
+match idu menv subst (Var v1) e2
+ | Just subst <- match_var idu menv subst v1 e2
= Just subst
-match menv subst e1 (Note _ e2)
- = match menv subst e1 e2
- -- Note [Notes in RULE matching]
- -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
- -- Look through Notes. In particular, we don't want to
- -- be confused by InlineMe notes. Maybe we should be more
- -- careful about profiling notes, but for now I'm just
- -- riding roughshod over them.
- --- See Note [Notes in call patterns] in SpecConstr
-
--- Here is another important rule: if the term being matched is a
--- variable, we expand it so long as its unfolding is a WHNF
--- (Its occurrence information is not necessarily up to date,
--- so we don't use it.)
-match menv subst e1 (Var v2)
- | isCheapUnfolding unfolding
- = match menv subst e1 (unfoldingTemplate unfolding)
+match idu menv subst (Note _ e1) e2 = match idu menv subst e1 e2
+match idu menv subst e1 (Note _ e2) = match idu menv subst e1 e2
+ -- Ignore notes in both template and thing to be matched
+ -- See Note [Notes in RULE matching]
+
+match id_unfolding_fun menv subst e1 (Var v2) -- Note [Expanding variables]
+ | not (inRnEnvR rn_env v2) -- Note [Do not expand locally-bound variables]
+ , Just e2' <- expandUnfolding_maybe (id_unfolding_fun v2')
+ = match id_unfolding_fun (menv { me_env = nukeRnEnvR rn_env }) subst e1 e2'
where
- rn_env = me_env menv
- unfolding = idUnfolding (lookupRnInScope rn_env (rnOccR rn_env v2))
+ v2' = lookupRnInScope rn_env v2
+ rn_env = me_env menv
-- Notice that we look up v2 in the in-scope set
-- See Note [Lookup in-scope]
- -- Remember to apply any renaming first (hence rnOccR)
-
--- Note [Matching lets]
--- ~~~~~~~~~~~~~~~~~~~~
--- Matching a let-expression. Consider
--- RULE forall x. f (g x) = <rhs>
--- and target expression
--- f (let { w=R } in g E))
--- Then we'd like the rule to match, to generate
--- let { w=R } in (\x. <rhs>) E
--- In effect, we want to float the let-binding outward, to enable
--- the match to happen. This is the WHOLE REASON for accumulating
--- bindings in the SubstEnv
---
--- We can only do this if
--- (a) Widening the scope of w does not capture any variables
--- We use a conservative test: w is not already in scope
--- If not, we clone the binders, and substitute
--- (b) The free variables of R are not bound by the part of the
--- target expression outside the let binding; e.g.
--- f (\v. let w = v+1 in g E)
--- Here we obviously cannot float the let-binding for w.
---
--- You may think rule (a) would never apply, because rule matching is
--- mostly invoked from the simplifier, when we have just run substExpr
--- over the argument, so there will be no shadowing anyway.
--- The fly in the ointment is that the forall'd variables of the
--- RULE itself are considered in scope.
---
--- I though of various cheapo ways to solve this tiresome problem,
--- but ended up doing the straightforward thing, which is to
--- clone the binders if they are in scope. It's tiresome, and
--- potentially inefficient, because of the calls to substExpr,
--- but I don't think it'll happen much in pracice.
+ -- No need to apply any renaming first (hence no rnOccR)
+ -- because of the not-inRnEnvR
-{- Cases to think about
- (let x=y+1 in \x. (x,x))
- --> let x=y+1 in (\x1. (x1,x1))
- (\x. let x = y+1 in (x,x))
- --> let x1 = y+1 in (\x. (x1,x1)
- (let x=y+1 in (x,x), let x=y-1 in (x,x))
- --> let x=y+1 in let x1=y-1 in ((x,x),(x1,x1))
-
-Watch out!
- (let x=y+1 in let z=x+1 in (z,z)
- --> matches (p,p) but watch out that the use of
- x on z's rhs is OK!
-I'm removing the cloning because that makes the above case
-fail, because the inner let looks as if it has locally-bound vars -}
-
-match menv (tv_subst, id_subst, binds) e1 (Let bind e2)
- | all freshly_bound bndrs,
- not (any locally_bound bind_fvs)
- = match (menv { me_env = rn_env' })
+match idu menv (tv_subst, id_subst, binds) e1 (Let bind e2)
+ | all freshly_bound bndrs -- See Note [Matching lets]
+ , not (any (inRnEnvR rn_env) bind_fvs)
+ = match idu (menv { me_env = rn_env' })
(tv_subst, id_subst, binds `snocOL` bind')
e1 e2'
where
rn_env = me_env menv
bndrs = bindersOf bind
bind_fvs = varSetElems (bindFreeVars bind)
- locally_bound x = inRnEnvR rn_env x
freshly_bound x = not (x `rnInScope` rn_env)
- bind' = bind
- e2' = e2
+ bind' = bind
+ e2' = e2
rn_env' = extendRnInScopeList rn_env bndrs
-{-
- (rn_env', bndrs') = mapAccumL rnBndrR rn_env bndrs
- s_prs = [(bndr, Var bndr') | (bndr,bndr') <- zip bndrs bndrs', bndr /= bndr']
- subst = mkSubst (rnInScopeSet rn_env) emptyVarEnv (mkVarEnv s_prs)
- (bind', e2') | null s_prs = (bind, e2)
- | otherwise = (s_bind, substExpr subst e2)
- s_bind = case bind of
- NonRec {} -> NonRec (head bndrs') (head rhss)
- Rec {} -> Rec (bndrs' `zip` map (substExpr subst) rhss)
--}
-
-match _ subst (Lit lit1) (Lit lit2)
+
+match _ _ subst (Lit lit1) (Lit lit2)
| lit1 == lit2
= Just subst
-match menv subst (App f1 a1) (App f2 a2)
- = do { subst' <- match menv subst f1 f2
- ; match menv subst' a1 a2 }
+match idu menv subst (App f1 a1) (App f2 a2)
+ = do { subst' <- match idu menv subst f1 f2
+ ; match idu menv subst' a1 a2 }
-match menv subst (Lam x1 e1) (Lam x2 e2)
- = match menv' subst e1 e2
+match idu menv subst (Lam x1 e1) (Lam x2 e2)
+ = match idu menv' subst e1 e2
where
menv' = menv { me_env = rnBndr2 (me_env menv) x1 x2 }
-- It's important that this is *after* the let rule,
-- so that (\x.M) ~ (let y = e in \y.N)
-- does the let thing, and then gets the lam/lam rule above
-match menv subst (Lam x1 e1) e2
- = match menv' subst e1 (App e2 (varToCoreExpr new_x))
+match idu menv subst (Lam x1 e1) e2
+ = match idu menv' subst e1 (App e2 (varToCoreExpr new_x))
where
(rn_env', new_x) = rnBndrL (me_env menv) x1
menv' = menv { me_env = rn_env' }
-- Eta expansion the other way
-- M ~ (\y.N) iff M y ~ N
-match menv subst e1 (Lam x2 e2)
- = match menv' subst (App e1 (varToCoreExpr new_x)) e2
+match idu menv subst e1 (Lam x2 e2)
+ = match idu menv' subst (App e1 (varToCoreExpr new_x)) e2
where
(rn_env', new_x) = rnBndrR (me_env menv) x2
menv' = menv { me_env = rn_env' }
-match menv subst (Case e1 x1 ty1 alts1) (Case e2 x2 ty2 alts2)
+match idu menv subst (Case e1 x1 ty1 alts1) (Case e2 x2 ty2 alts2)
= do { subst1 <- match_ty menv subst ty1 ty2
- ; subst2 <- match menv subst1 e1 e2
+ ; subst2 <- match idu menv subst1 e1 e2
; let menv' = menv { me_env = rnBndr2 (me_env menv) x1 x2 }
- ; match_alts menv' subst2 alts1 alts2 -- Alts are both sorted
+ ; match_alts idu menv' subst2 alts1 alts2 -- Alts are both sorted
}
-match menv subst (Type ty1) (Type ty2)
+match _ menv subst (Type ty1) (Type ty2)
= match_ty menv subst ty1 ty2
-match menv subst (Cast e1 co1) (Cast e2 co2)
+match idu menv subst (Cast e1 co1) (Cast e2 co2)
= do { subst1 <- match_ty menv subst co1 co2
- ; match menv subst1 e1 e2 }
-
-{- REMOVING OLD CODE: I think that the above handling for let is
- better than the stuff here, which looks
- pretty suspicious to me. SLPJ Sept 06
--- This is an interesting rule: we simply ignore lets in the
--- term being matched against! The unfolding inside it is (by assumption)
--- already inside any occurrences of the bound variables, so we'll expand
--- them when we encounter them. This gives a chance of matching
--- forall x,y. f (g (x,y))
--- against
--- f (let v = (a,b) in g v)
-
-match menv subst e1 (Let bind e2)
- = match (menv { me_env = rn_env' }) subst e1 e2
- where
- (rn_env', _bndrs') = mapAccumL rnBndrR (me_env menv) (bindersOf bind)
- -- It's important to do this renaming, so that the bndrs
- -- are brought into the local scope. For example:
- -- Matching
- -- forall f,x,xs. f (x:xs)
- -- against
- -- f (let y = e in (y:[]))
- -- We must not get success with x->y! So we record that y is
- -- locally bound (with rnBndrR), and proceed. The Var case
- -- will fail when trying to bind x->y
--}
+ ; match idu menv subst1 e1 e2 }
-- Everything else fails
-match _ _ _e1 _e2 = -- pprTrace "Failing at" ((text "e1:" <+> ppr e1) $$ (text "e2:" <+> ppr e2)) $
+match _ _ _ _e1 _e2 = -- pprTrace "Failing at" ((text "e1:" <+> ppr _e1) $$ (text "e2:" <+> ppr _e2)) $
Nothing
------------------------------------------
-match_var :: MatchEnv
+match_var :: IdUnfoldingFun
+ -> MatchEnv
-> SubstEnv
-> Var -- Template
-> CoreExpr -- Target
-> Maybe SubstEnv
-match_var menv subst@(tv_subst, id_subst, binds) v1 e2
+match_var idu menv subst@(tv_subst, id_subst, binds) v1 e2
| v1' `elemVarSet` me_tmpls menv
= case lookupVarEnv id_subst v1' of
Nothing | any (inRnEnvR rn_env) (varSetElems (exprFreeVars e2))
-- c.f. match_ty below
; return (tv_subst', extendVarEnv id_subst v1' e2, binds) }
- Just e1' | tcEqExprX (nukeRnEnvL rn_env) e1' e2
+ Just e1' | eqExprX idu (nukeRnEnvL rn_env) e1' e2
-> Just subst
| otherwise
------------------------------------------
-match_alts :: MatchEnv
- -> SubstEnv
- -> [CoreAlt] -- Template
- -> [CoreAlt] -- Target
- -> Maybe SubstEnv
-match_alts _ subst [] []
+match_alts :: IdUnfoldingFun
+ -> MatchEnv
+ -> SubstEnv
+ -> [CoreAlt] -- Template
+ -> [CoreAlt] -- Target
+ -> Maybe SubstEnv
+match_alts _ _ subst [] []
= return subst
-match_alts menv subst ((c1,vs1,r1):alts1) ((c2,vs2,r2):alts2)
+match_alts idu menv subst ((c1,vs1,r1):alts1) ((c2,vs2,r2):alts2)
| c1 == c2
- = do { subst1 <- match menv' subst r1 r2
- ; match_alts menv subst1 alts1 alts2 }
+ = do { subst1 <- match idu menv' subst r1 r2
+ ; match_alts idu menv subst1 alts1 alts2 }
where
menv' :: MatchEnv
menv' = menv { me_env = rnBndrs2 (me_env menv) vs1 vs2 }
-match_alts _ _ _ _
+match_alts _ _ _ _ _
= Nothing
\end{code}
; return (tv_subst', id_subst, binds) }
\end{code}
+Note [Expanding variables]
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+Here is another Very Important rule: if the term being matched is a
+variable, we expand it so long as its unfolding is "expandable". (Its
+occurrence information is not necessarily up to date, so we don't use
+it.) By "expandable" we mean a WHNF or a "constructor-like" application.
+This is the key reason for "constructor-like" Ids. If we have
+ {-# NOINLINE [1] CONLIKE g #-}
+ {-# RULE f (g x) = h x #-}
+then in the term
+ let v = g 3 in ....(f v)....
+we want to make the rule fire, to replace (f v) with (h 3).
+
+Note [Do not expand locally-bound variables]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Do *not* expand locally-bound variables, else there's a worry that the
+unfolding might mention variables that are themselves renamed.
+Example
+ case x of y { (p,q) -> ...y... }
+Don't expand 'y' to (p,q) because p,q might themselves have been
+renamed. Essentially we only expand unfoldings that are "outside"
+the entire match.
+
+Hence, (a) the guard (not (isLocallyBoundR v2))
+ (b) when we expand we nuke the renaming envt (nukeRnEnvR).
+
+Note [Notes in RULE matching]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Look through Notes in both template and expression being matched. In
+particular, we don't want to be confused by InlineMe notes. Maybe we
+should be more careful about profiling notes, but for now I'm just
+riding roughshod over them. cf Note [Notes in call patterns] in
+SpecConstr
+
+Note [Matching lets]
+~~~~~~~~~~~~~~~~~~~~
+Matching a let-expression. Consider
+ RULE forall x. f (g x) = <rhs>
+and target expression
+ f (let { w=R } in g E))
+Then we'd like the rule to match, to generate
+ let { w=R } in (\x. <rhs>) E
+In effect, we want to float the let-binding outward, to enable
+the match to happen. This is the WHOLE REASON for accumulating
+bindings in the SubstEnv
+
+We can only do this if
+ (a) Widening the scope of w does not capture any variables
+ We use a conservative test: w is not already in scope
+ If not, we clone the binders, and substitute
+ (b) The free variables of R are not bound by the part of the
+ target expression outside the let binding; e.g.
+ f (\v. let w = v+1 in g E)
+ Here we obviously cannot float the let-binding for w.
+
+You may think rule (a) would never apply, because rule matching is
+mostly invoked from the simplifier, when we have just run substExpr
+over the argument, so there will be no shadowing anyway.
+The fly in the ointment is that the forall'd variables of the
+RULE itself are considered in scope.
+
+I though of various ways to solve (a). One plan was to
+clone the binders if they are in scope. But watch out!
+ (let x=y+1 in let z=x+1 in (z,z)
+ --> should match (p,p) but watch out that
+ the use of x on z's rhs is OK!
+If we clone x, then the let-binding for 'z' is then caught by (b),
+at least unless we elaborate the RnEnv stuff a bit.
+
+So for we simply fail to match unless both (a) and (b) hold.
+
+Other cases to think about
+ (let x=y+1 in \x. (x,x))
+ --> let x=y+1 in (\x1. (x1,x1))
+ (\x. let x = y+1 in (x,x))
+ --> let x1 = y+1 in (\x. (x1,x1)
+ (let x=y+1 in (x,x), let x=y-1 in (x,x))
+ --> let x=y+1 in let x1=y-1 in ((x,x),(x1,x1))
+
Note [Lookup in-scope]
~~~~~~~~~~~~~~~~~~~~~~
That is why the 'lookupRnInScope' call in the (Var v2) case of 'match'
is so important.
-
%************************************************************************
%* *
-\subsection{Checking a program for failing rule applications}
+ Rule-check the program
%* *
%************************************************************************
------------------------------------------------------
- Game plan
------------------------------------------------------
-
-We want to know what sites have rules that could have fired but didn't.
-This pass runs over the tree (without changing it) and reports such.
+ We want to know what sites have rules that could have fired but didn't.
+ This pass runs over the tree (without changing it) and reports such.
\begin{code}
-- | Report partial matches for rules beginning with the specified
-- string for the purposes of error reporting
-ruleCheckProgram :: (Activation -> Bool) -- ^ Rule activation test
+ruleCheckProgram :: CompilerPhase -- ^ Rule activation test
-> String -- ^ Rule pattern
-> RuleBase -- ^ Database of rules
-> [CoreBind] -- ^ Bindings to check in
-> SDoc -- ^ Resulting check message
-ruleCheckProgram is_active rule_pat rule_base binds
+ruleCheckProgram phase rule_pat rule_base binds
| isEmptyBag results
= text "Rule check results: no rule application sites"
| otherwise
vcat [ p $$ line | p <- bagToList results ]
]
where
- results = unionManyBags (map (ruleCheckBind (RuleCheckEnv is_active rule_pat rule_base)) binds)
+ env = RuleCheckEnv { rc_is_active = isActive phase
+ , rc_id_unf = idUnfolding -- Not quite right
+ -- Should use activeUnfolding
+ , rc_pattern = rule_pat
+ , rc_rule_base = rule_base }
+ results = unionManyBags (map (ruleCheckBind env) binds)
line = text (replicate 20 '-')
data RuleCheckEnv = RuleCheckEnv {
rc_is_active :: Activation -> Bool,
+ rc_id_unf :: IdUnfoldingFun,
rc_pattern :: String,
rc_rule_base :: RuleBase
}
ruleCheckFun env fn args
| null name_match_rules = emptyBag
- | otherwise = unitBag (ruleAppCheck_help (rc_is_active env) fn args name_match_rules)
+ | otherwise = unitBag (ruleAppCheck_help env fn args name_match_rules)
where
name_match_rules = filter match (getRules (rc_rule_base env) fn)
match rule = (rc_pattern env) `isPrefixOf` unpackFS (ruleName rule)
-ruleAppCheck_help :: (Activation -> Bool) -> Id -> [CoreExpr] -> [CoreRule] -> SDoc
-ruleAppCheck_help is_active fn args rules
+ruleAppCheck_help :: RuleCheckEnv -> Id -> [CoreExpr] -> [CoreRule] -> SDoc
+ruleAppCheck_help env fn args rules
= -- The rules match the pattern, so we want to print something
vcat [text "Expression:" <+> ppr (mkApps (Var fn) args),
vcat (map check_rule rules)]
= ptext (sLit "Rule") <+> doubleQuotes (ftext name)
rule_info rule
- | Just _ <- matchRule noBlackList emptyInScopeSet args rough_args rule
+ | Just _ <- matchRule noBlackList (rc_id_unf env) emptyInScopeSet args rough_args rule
= text "matches (which is very peculiar!)"
rule_info (BuiltinRule {}) = text "does not match"
rule_info (Rule { ru_act = act,
ru_bndrs = rule_bndrs, ru_args = rule_args})
- | not (is_active act) = text "active only in later phase"
+ | not (rc_is_active env act) = text "active only in later phase"
| n_args < n_rule_args = text "too few arguments"
| n_mismatches == n_rule_args = text "no arguments match"
| n_mismatches == 0 = text "all arguments match (considered individually), but rule as a whole does not"
not (isJust (match_fn rule_arg arg))]
lhs_fvs = exprsFreeVars rule_args -- Includes template tyvars
- match_fn rule_arg arg = match menv emptySubstEnv rule_arg arg
+ match_fn rule_arg arg = match (rc_id_unf env) menv emptySubstEnv rule_arg arg
where
in_scope = lhs_fvs `unionVarSet` exprFreeVars arg
menv = ME { me_env = mkRnEnv2 (mkInScopeSet in_scope)