\section[CoreRules]{Transformation rules}
\begin{code}
+-- | Functions for collecting together and applying rewrite rules to a module.
+-- The 'CoreRule' datatype itself is declared elsewhere.
module Rules (
- RuleBase, emptyRuleBase, mkRuleBase, extendRuleBaseList,
- unionRuleBase, pprRuleBase, ruleCheckProgram,
+ -- * RuleBase
+ RuleBase,
+
+ -- ** Constructing
+ emptyRuleBase, mkRuleBase, extendRuleBaseList,
+ unionRuleBase, pprRuleBase,
+
+ -- ** Checking rule applications
+ ruleCheckProgram,
+ -- ** Manipulating 'SpecInfo' rules
mkSpecInfo, extendSpecInfo, addSpecInfo,
- rulesOfBinds, addIdSpecialisations,
+ addIdSpecialisations,
- matchN,
-
- lookupRule, mkLocalRule, roughTopNames
+ -- * Misc. CoreRule helpers
+ rulesOfBinds, getRules, pprRulesForUser,
+
+ lookupRule, mkRule, roughTopNames
) where
#include "HsVersions.h"
import CoreSyn -- All of it
-import OccurAnal ( occurAnalyseExpr )
-import CoreFVs ( exprFreeVars, exprsFreeVars, bindFreeVars, rulesRhsFreeVars )
-import CoreUnfold ( isCheapUnfolding, unfoldingTemplate )
-import CoreUtils ( tcEqExprX )
+import CoreSubst
+import OccurAnal ( occurAnalyseExpr )
+import CoreFVs ( exprFreeVars, exprsFreeVars, bindFreeVars, rulesFreeVars )
+import CoreUtils ( exprType, eqExpr )
import PprCore ( pprRules )
-import Type ( TvSubstEnv )
-import Coercion ( coercionKind )
+import Type ( Type )
import TcType ( tcSplitTyConApp_maybe )
+import Coercion
import CoreTidy ( tidyRules )
-import Id ( Id, idUnfolding, isLocalId, isGlobalId, idName,
- idSpecialisation, idCoreRules, setIdSpecialisation )
+import Id
import IdInfo ( SpecInfo( SpecInfo ) )
-import Var ( Var )
-import VarEnv ( IdEnv, InScopeSet, emptyTidyEnv,
- emptyInScopeSet, mkInScopeSet,
- emptyVarEnv, lookupVarEnv, extendVarEnv,
- nukeRnEnvL, mkRnEnv2, rnOccR, rnOccL, inRnEnvR,
- rnBndrR, rnBndr2, rnBndrL, rnBndrs2,
- rnInScope, extendRnInScopeList, lookupRnInScope )
+import VarEnv
import VarSet
-import Name ( Name, NamedThing(..), nameOccName )
+import Name ( Name, NamedThing(..) )
import NameEnv
import Unify ( ruleMatchTyX, MatchEnv(..) )
import BasicTypes ( Activation, CompilerPhase, isActive )
+import StaticFlags ( opt_PprStyle_Debug )
import Outputable
import FastString
import Maybes
-import OrdList
import Bag
import Util
-import List hiding( mapAccumL ) -- Also defined in Util
+import Data.List
\end{code}
+Note [Overall plumbing for rules]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+* After the desugarer:
+ - The ModGuts initially contains mg_rules :: [CoreRule] of
+ locally-declared rules for imported Ids.
+ - Locally-declared rules for locally-declared Ids are attached to
+ the IdInfo for that Id. See Note [Attach rules to local ids] in
+ DsBinds
+
+* TidyPgm strips off all the rules from local Ids and adds them to
+ mg_rules, so that the ModGuts has *all* the locally-declared rules.
+
+* 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 why 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.]
+
%************************************************************************
%* *
where pi' :: Lift Int# is the specialised version of pi.
\begin{code}
-mkLocalRule :: RuleName -> Activation
- -> Name -> [CoreBndr] -> [CoreExpr] -> CoreExpr -> CoreRule
--- Used to make CoreRule for an Id defined in this module
-mkLocalRule name act fn bndrs args rhs
+mkRule :: Bool -> 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_auto 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_orph = Just (nameOccName fn), ru_local = True }
+ ru_rhs = occurAnalyseExpr rhs,
+ ru_rough = roughTopNames args,
+ ru_auto = is_auto, ru_local = is_local }
--------------
roughTopNames :: [CoreExpr] -> [Maybe Name]
+-- ^ Find the \"top\" free names of several expressions.
+-- Such names are either:
+--
+-- 1. The function finally being applied to in an application chain
+-- (if that name is a GlobalId: see "Var#globalvslocal"), or
+--
+-- 2. The 'TyCon' if the expression is a 'Type'
+--
+-- This is used for the fast-match-check for rules;
+-- if the top names don't match, the rest can't
roughTopNames args = map roughTopName args
roughTopName :: CoreExpr -> Maybe Name
--- Find the "top" free name of an expression
--- a) the function in an App chain (if a GlobalId)
--- b) the TyCon in a type
--- This is used for the fast-match-check for rules;
--- if the top names don't match, the rest can't
roughTopName (Type ty) = case tcSplitTyConApp_maybe ty of
- Just (tc,_) -> Just (getName tc)
- Nothing -> Nothing
-roughTopName (App f a) = roughTopName f
-roughTopName (Var f) | isGlobalId f = Just (idName f)
- | otherwise = Nothing
-roughTopName other = Nothing
+ Just (tc,_) -> Just (getName tc)
+ Nothing -> Nothing
+roughTopName (Coercion _) = Nothing
+roughTopName (App f _) = roughTopName f
+roughTopName (Var f) | isGlobalId f -- Note [Care with roughTopName]
+ , isDataConWorkId f || idArity f > 0
+ = Just (idName f)
+roughTopName _ = Nothing
ruleCantMatch :: [Maybe Name] -> [Maybe Name] -> Bool
--- (ruleCantMatch tpl actual) returns True only if 'actual'
--- definitely can't match 'tpl' by instantiating 'tpl'.
+-- ^ @ruleCantMatch tpl actual@ returns True only if @actual@
+-- definitely can't match @tpl@ by instantiating @tpl@.
-- It's only a one-way match; unlike instance matching we
--- don't consider unification
+-- don't consider unification.
--
--- Notice that there is no case
--- ruleCantMatch (Just n1 : ts) (Nothing : as) = True
--- Reason: a local variable 'v' in the actuals might
--- have an unfolding which is a global.
--- This quite often happens with case scrutinees.
+-- Notice that [_$_]
+-- @ruleCantMatch [Nothing] [Just n2] = False@
+-- Reason: a template variable can be instantiated by a constant
+-- Also:
+-- @ruleCantMatch [Just n1] [Nothing] = False@
+-- Reason: a local variable @v@ in the actuals might [_$_]
+
ruleCantMatch (Just n1 : ts) (Just n2 : as) = n1 /= n2 || ruleCantMatch ts as
-ruleCantMatch (t : ts) (a : as) = ruleCantMatch ts as
-ruleCantMatch ts as = False
+ruleCantMatch (_ : ts) (_ : as) = ruleCantMatch ts as
+ruleCantMatch _ _ = False
+\end{code}
+
+Note [Care with roughTopName]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Consider this
+ module M where { x = a:b }
+ module N where { ...f x...
+ RULE f (p:q) = ... }
+You'd expect the rule to match, because the matcher can
+look through the unfolding of 'x'. So we must avoid roughTopName
+returning 'M.x' for the call (f x), or else it'll say "can't match"
+and we won't even try!!
+
+However, suppose we have
+ RULE g (M.h x) = ...
+ foo = ...(g (M.k v))....
+where k is a *function* exported by M. We never really match
+functions (lambdas) except by name, so in this case it seems like
+a good idea to treat 'M.k' as a roughTopName of the call.
+
+
+\begin{code}
+pprRulesForUser :: [CoreRule] -> SDoc
+-- (a) tidy the rules
+-- (b) sort them into order based on the rule name
+-- (c) suppress uniques (unless -dppr-debug is on)
+-- This combination makes the output stable so we can use in testing
+-- It's here rather than in PprCore because it calls tidyRules
+pprRulesForUser rules
+ = withPprStyle defaultUserStyle $
+ pprRules $
+ sortLe le_rule $
+ tidyRules emptyTidyEnv rules
+ where
+ le_rule r1 r2 = ru_name r1 <= ru_name r2
\end{code}
%************************************************************************
\begin{code}
+-- | Make a 'SpecInfo' containing a number of 'CoreRule's, suitable
+-- for putting into an 'IdInfo'
mkSpecInfo :: [CoreRule] -> SpecInfo
-mkSpecInfo rules = SpecInfo rules (rulesRhsFreeVars rules)
+mkSpecInfo rules = SpecInfo rules (rulesFreeVars rules)
extendSpecInfo :: SpecInfo -> [CoreRule] -> SpecInfo
extendSpecInfo (SpecInfo rs1 fvs1) rs2
- = SpecInfo (rs2 ++ rs1) (rulesRhsFreeVars rs2 `unionVarSet` fvs1)
+ = SpecInfo (rs2 ++ rs1) (rulesFreeVars rs2 `unionVarSet` fvs1)
addSpecInfo :: SpecInfo -> SpecInfo -> SpecInfo
addSpecInfo (SpecInfo rs1 fvs1) (SpecInfo rs2 fvs2)
= SpecInfo (rs1 ++ rs2) (fvs1 `unionVarSet` fvs2)
addIdSpecialisations :: Id -> [CoreRule] -> Id
+addIdSpecialisations id []
+ = id
addIdSpecialisations id rules
= setIdSpecialisation id $
extendSpecInfo (idSpecialisation id) rules
+-- | Gather all the rules for locally bound identifiers from the supplied bindings
rulesOfBinds :: [CoreBind] -> [CoreRule]
rulesOfBinds binds = concatMap (concatMap idCoreRules . bindersOf) binds
+
+getRules :: RuleBase -> Id -> [CoreRule]
+-- See Note [Where rules are found]
+getRules rule_base fn
+ = 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
+
%************************************************************************
%* *
%************************************************************************
\begin{code}
+-- | Gathers a collection of 'CoreRule's. Maps (the name of) an 'Id' to its rules
type RuleBase = NameEnv [CoreRule]
- -- Maps (the name of) an Id to its rules
-- The rules are are unordered;
-- we sort out any overlaps on lookup
+emptyRuleBase :: RuleBase
emptyRuleBase = emptyNameEnv
mkRuleBase :: [CoreRule] -> RuleBase
%************************************************************************
%* *
-\subsection{Matching}
+ Matching
%* *
%************************************************************************
\begin{code}
-lookupRule :: (Activation -> Bool) -> InScopeSet
- -> RuleBase -- Imported rules
- -> Id -> [CoreExpr] -> Maybe (CoreRule, CoreExpr)
-lookupRule is_active in_scope rule_base fn args
- = matchRules is_active in_scope fn args rules
- where
- -- 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)
- rules = extra_rules ++ idCoreRules fn
- extra_rules | isLocalId fn = []
- | otherwise = lookupNameEnv rule_base (idName fn) `orElse` []
-
-matchRules :: (Activation -> Bool) -> InScopeSet
- -> Id -> [CoreExpr]
- -> [CoreRule] -> Maybe (CoreRule, CoreExpr)
+-- | The main rule matching function. Attempts to apply all (active)
+-- 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) -- 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
-matchRules is_active in_scope fn args rules
- = -- pprTrace "matchRules" (ppr fn <+> ppr rules) $
+lookupRule is_active id_unf in_scope fn args rules
+ = -- pprTrace "matchRules" (ppr fn <+> ppr args $$ ppr rules ) $
case go [] rules of
[] -> Nothing
(m:ms) -> Just (findBest (fn,args) m ms)
go :: [(CoreRule,CoreExpr)] -> [CoreRule] -> [(CoreRule,CoreExpr)]
go ms [] = ms
- go ms (r:rs) = case (matchRule is_active in_scope args rough_args r) of
+ go ms (r:rs) = case (matchRule is_active id_unf in_scope args rough_args r) of
Just e -> go ((r,e):ms) rs
Nothing -> -- pprTrace "match failed" (ppr r $$ ppr args $$
- -- ppr [(arg_id, unfoldingTemplate unf) | Var arg_id <- args, let unf = idUnfolding arg_id, isCheapUnfolding unf] )
- go ms rs
+ -- ppr [ (arg_id, unfoldingTemplate unf)
+ -- | Var arg_id <- args
+ -- , let unf = idUnfolding arg_id
+ -- , isCheapUnfolding unf] )
+ go ms rs
findBest :: (Id, [CoreExpr])
-> (CoreRule,CoreExpr) -> [(CoreRule,CoreExpr)] -> (CoreRule,CoreExpr)
-- Return the pair the the most specific rule
-- The (fn,args) is just for overlap reporting
-findBest target (rule,ans) [] = (rule,ans)
+findBest _ (rule,ans) [] = (rule,ans)
findBest target (rule1,ans1) ((rule2,ans2):prs)
| rule1 `isMoreSpecific` rule2 = findBest target (rule1,ans1) prs
| rule2 `isMoreSpecific` rule1 = findBest target (rule2,ans2) prs
-#ifdef DEBUG
- | otherwise = pprTrace "Rules.findBest: rule overlap (Rule 1 wins)"
- (vcat [ptext SLIT("Expression to match:") <+> ppr fn <+> sep (map ppr args),
- ptext SLIT("Rule 1:") <+> ppr rule1,
- ptext SLIT("Rule 2:") <+> ppr rule2]) $
+ | debugIsOn = let pp_rule rule
+ | opt_PprStyle_Debug = ppr rule
+ | otherwise = doubleQuotes (ftext (ru_name rule))
+ in pprTrace "Rules.findBest: rule overlap (Rule 1 wins)"
+ (vcat [if opt_PprStyle_Debug then
+ ptext (sLit "Expression to match:") <+> ppr fn <+> sep (map ppr args)
+ else empty,
+ ptext (sLit "Rule 1:") <+> pp_rule rule1,
+ ptext (sLit "Rule 2:") <+> pp_rule rule2]) $
findBest target (rule1,ans1) prs
-#else
| otherwise = findBest target (rule1,ans1) prs
-#endif
where
(fn,args) = target
isMoreSpecific :: CoreRule -> CoreRule -> Bool
-isMoreSpecific (BuiltinRule {}) r2 = True
-isMoreSpecific r1 (BuiltinRule {}) = False
+-- This tests if one rule is more specific than another
+-- We take the view that a BuiltinRule is less specific than
+-- anything else, because we want user-define rules to "win"
+-- In particular, class ops have a built-in rule, but we
+-- any user-specific rules to win
+-- eg (Trac #4397)
+-- truncate :: (RealFrac a, Integral b) => a -> b
+-- {-# RULES "truncate/Double->Int" truncate = double2Int #-}
+-- double2Int :: Double -> Int
+-- We want the specific RULE to beat the built-in class-op rule
+isMoreSpecific (BuiltinRule {}) _ = False
+isMoreSpecific (Rule {}) (BuiltinRule {}) = True
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 act = False -- Nothing is black listed
+noBlackList _ = False -- Nothing is black listed
+\end{code}
+
+Note [Extra args in rule matching]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+If we find a matching rule, we return (Just (rule, rhs)),
+but the rule firing has only consumed as many of the input args
+as the ruleArity says. It's up to the caller to keep track
+of any left-over args. E.g. if you call
+ lookupRule ... f [e1, e2, e3]
+and it returns Just (r, rhs), where r has ruleArity 2
+then the real rewrite is
+ f e1 e2 e3 ==> rhs e3
+
+You might think it'd be cleaner for lookupRule to deal with the
+leftover arguments, by applying 'rhs' to them, but the main call
+in the Simplifier works better as it is. Reason: the 'args' passed
+to lookupRule are the result of a lazy substitution
-matchRule :: (Activation -> Bool) -> InScopeSet
+\begin{code}
+------------------------------------
+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
- (BuiltinRule { ru_name = name, ru_try = match_fn })
- = case match_fn args of
+matchRule _is_active id_unf _in_scope args _rough_args
+ (BuiltinRule { ru_try = match_fn })
+-- 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
- (Rule { ru_name = rn, ru_act = act, ru_rough = tpl_tops,
+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
- Nothing -> Nothing
- Just (binds, tpl_vals) -> Just (mkLets binds $
- rule_fn `mkApps` tpl_vals)
+ = case matchN id_unf in_scope tpl_vars tpl_args args of
+ Nothing -> Nothing
+ Just (bind_wrapper, tpl_vals) -> Just (bind_wrapper $
+ rule_fn `mkApps` tpl_vals)
where
rule_fn = occurAnalyseExpr (mkLams tpl_vars rhs)
-- We could do this when putting things into the rulebase, I guess
-\end{code}
-\begin{code}
-matchN :: InScopeSet
- -> [Var] -- Template tyvars
- -> [CoreExpr] -- Template
- -> [CoreExpr] -- Target; can have more elts than template
- -> Maybe ([CoreBind], -- Bindings to wrap around the entire result
- [CoreExpr]) -- What is substituted for each template var
-
-matchN 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,
- map (lookup_tmpl tv_subst id_subst) tmpl_vars') }
+---------------------------------------
+matchN :: IdUnfoldingFun
+ -> InScopeSet -- ^ In-scope variables
+ -> [Var] -- ^ Match template type variables
+ -> [CoreExpr] -- ^ Match template
+ -> [CoreExpr] -- ^ Target; can have more elements than the template
+ -> Maybe (BindWrapper, -- Floated bindings; see Note [Matching lets]
+ [CoreExpr])
+-- 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 id_unf in_scope tmpl_vars tmpl_es target_es
+ = do { subst <- go init_menv emptyRuleSubst tmpl_es target_es
+ ; return (rs_binds subst,
+ map (lookup_tmpl subst) tmpl_vars') }
where
(init_rn_env, tmpl_vars') = mapAccumL rnBndrL (mkRnEnv2 in_scope) tmpl_vars
- -- See Note [Template binders]
+ -- See Note [Template binders]
- init_menv = ME { me_tmpls = mkVarSet tmpl_vars', me_env = init_rn_env }
+ init_menv = RV { rv_tmpls = mkVarSet tmpl_vars', rv_lcl = init_rn_env
+ , rv_fltR = mkEmptySubst (rnInScopeSet init_rn_env)
+ , rv_unf = id_unf }
- go menv subst [] es = Just subst
- go menv subst ts [] = Nothing -- Fail if too few actual args
- go menv subst (t:ts) (e:es) = do { subst1 <- match menv subst t e
+ 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 subst1 ts es }
- lookup_tmpl :: TvSubstEnv -> IdSubstEnv -> Var -> CoreExpr
- lookup_tmpl tv_subst id_subst tmpl_var'
- | isTyVar tmpl_var' = case lookupVarEnv tv_subst tmpl_var' of
- Just ty -> Type ty
- Nothing -> unbound tmpl_var'
- | otherwise = case lookupVarEnv id_subst tmpl_var' of
- Just e -> e
- other -> unbound tmpl_var'
-
- unbound var = pprPanic "Template variable unbound in rewrite rule" (ppr var)
+ lookup_tmpl :: RuleSubst -> Var -> CoreExpr
+ lookup_tmpl (RS { rs_tv_subst = tv_subst, rs_id_subst = id_subst }) tmpl_var'
+ | isId tmpl_var' = case lookupVarEnv id_subst tmpl_var' of
+ Just e -> e
+ _ -> unbound tmpl_var'
+ | otherwise = case lookupVarEnv tv_subst tmpl_var' of
+ Just ty -> Type ty
+ Nothing -> unbound tmpl_var'
+
+ unbound var = pprPanic "Template variable unbound in rewrite rule"
+ (ppr var $$ ppr tmpl_vars $$ ppr tmpl_vars' $$ ppr tmpl_es $$ ppr target_es)
\end{code}
Note [Template binders]
~~~~~~~~~~~~~~~~~~~~~~~
Consider the following match:
Template: forall x. f x
- Taret: f (x+1)
-This should succeed, because the template variable 'x' has nothing to do with
-the 'x' in the target.
+ Target: f (x+1)
+This should succeed, because the template variable 'x' has
+nothing to do with the 'x' in the target.
-To achive this, we use rnBndrL to rename the template variables if necessary;
-the renamed ones are the tmpl_vars'
+On reflection, this case probably does just work, but this might not
+ Template: forall x. f (\x.x)
+ Target: f (\y.y)
+Here we want to clone when we find the \x, but to know that x must be in scope
+To achive this, we use rnBndrL to rename the template variables if
+necessary; the renamed ones are the tmpl_vars'
- ---------------------------------------------
+
+%************************************************************************
+%* *
+ The main matcher
+%* *
+%************************************************************************
+
+ ---------------------------------------------
The inner workings of matching
---------------------------------------------
\begin{code}
--- These two definitions are not the same as in Subst,
--- but they simple and direct, and purely local to this module
---
-- * The domain of the TvSubstEnv and IdSubstEnv are the template
-- variables passed into the match.
--
--- * The (OrdList CoreBind) in a SubstEnv are the bindings floated out
+-- * The BindWrapper in a RuleSubst are the bindings floated out
-- from nested matches; see the Let case of match, below
--
-type SubstEnv = (TvSubstEnv, IdSubstEnv, OrdList CoreBind)
-type IdSubstEnv = IdEnv CoreExpr
-
-emptySubstEnv :: SubstEnv
-emptySubstEnv = (emptyVarEnv, emptyVarEnv, nilOL)
-
+data RuleEnv = RV { rv_tmpls :: VarSet -- Template variables
+ , rv_lcl :: RnEnv2 -- Renamings for *local bindings*
+ -- (lambda/case)
+ , rv_fltR :: Subst -- Renamings for floated let-bindings
+ -- domain disjoint from envR of rv_lcl
+ -- See Note [Matching lets]
+ , rv_unf :: IdUnfoldingFun
+ }
+
+data RuleSubst = RS { rs_tv_subst :: TvSubstEnv -- Range is the
+ , rs_id_subst :: IdSubstEnv -- template variables
+ , rs_binds :: BindWrapper -- Floated bindings
+ , rs_bndrs :: VarSet -- Variables bound by floated lets
+ }
+
+type BindWrapper = CoreExpr -> CoreExpr
+ -- See Notes [Matching lets] and [Matching cases]
+ -- we represent the floated bindings as a core-to-core function
+
+emptyRuleSubst :: RuleSubst
+emptyRuleSubst = RS { rs_tv_subst = emptyVarEnv, rs_id_subst = emptyVarEnv
+ , rs_binds = \e -> e, rs_bndrs = emptyVarSet }
-- At one stage I tried to match even if there are more
-- template args than real args.
-- SLPJ July 99
-match :: MatchEnv
- -> SubstEnv
+match :: RuleEnv
+ -> RuleSubst
-> CoreExpr -- Template
-> CoreExpr -- Target
- -> Maybe SubstEnv
+ -> Maybe RuleSubst
-- See the notes with Unify.match, which matches types
-- Everything is very similar for terms
-- 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
- = Just subst
-
-match menv subst e1 (Note n 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 renv subst (Var v1) e2 = match_var renv subst v1 e2
+match renv subst (Note _ e1) e2 = match renv subst e1 e2
+match renv subst e1 (Note _ e2) = match renv subst e1 e2
+ -- Ignore notes in both template and thing to be matched
+ -- See Note [Notes in RULE matching]
+
+match renv subst e1 (Var v2) -- Note [Expanding variables]
+ | not (inRnEnvR rn_env v2) -- Note [Do not expand locally-bound variables]
+ , Just e2' <- expandUnfolding_maybe (rv_unf renv v2')
+ = match (renv { rv_lcl = 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 = rv_lcl renv
-- Notice that we look up v2 in the in-scope set
-- See Note [Lookup in-scope]
- -- Remember to apply any renaming first (hence rnOccR)
-
--- 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
--- (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.
-
-match menv subst@(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' })
- (tv_subst, id_subst, binds `snocOL` bind)
+ -- No need to apply any renaming first (hence no rnOccR)
+ -- because of the not-inRnEnvR
+
+match renv subst e1 (Let bind e2)
+ | okToFloat (rv_lcl renv) (bindFreeVars bind) -- See Note [Matching lets]
+ = match (renv { rv_fltR = flt_subst' })
+ (subst { rs_binds = rs_binds subst . Let bind'
+ , rs_bndrs = extendVarSetList (rs_bndrs subst) new_bndrs })
e1 e2
where
- rn_env = me_env menv
- bndrs = bindersOf bind
- bind_fvs = varSetElems (bindFreeVars bind)
- freshly_bound x = not (x `rnInScope` rn_env)
- locally_bound x = inRnEnvR rn_env x
- rn_env' = extendRnInScopeList rn_env bndrs
-
-match menv subst (Lit lit1) (Lit lit2)
+ flt_subst = addInScopeSet (rv_fltR renv) (rs_bndrs subst)
+ (flt_subst', bind') = substBind flt_subst bind
+ new_bndrs = bindersOf bind'
+
+{- Disabled: see Note [Matching cases] below
+match renv (tv_subst, id_subst, binds) e1
+ (Case scrut case_bndr ty [(con, alt_bndrs, rhs)])
+ | exprOkForSpeculation scrut -- See Note [Matching cases]
+ , okToFloat rn_env bndrs (exprFreeVars scrut)
+ = match (renv { me_env = rn_env' })
+ (tv_subst, id_subst, binds . case_wrap)
+ e1 rhs
+ where
+ rn_env = me_env renv
+ rn_env' = extendRnInScopeList rn_env bndrs
+ bndrs = case_bndr : alt_bndrs
+ case_wrap rhs' = Case scrut case_bndr ty [(con, alt_bndrs, rhs')]
+-}
+
+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 renv subst (App f1 a1) (App f2 a2)
+ = do { subst' <- match renv subst f1 f2
+ ; match renv subst' a1 a2 }
-match menv subst (Lam x1 e1) (Lam x2 e2)
- = match menv' subst e1 e2
+match renv subst (Lam x1 e1) (Lam x2 e2)
+ = match renv' subst e1 e2
where
- menv' = menv { me_env = rnBndr2 (me_env menv) x1 x2 }
+ renv' = renv { rv_lcl = rnBndr2 (rv_lcl renv) x1 x2
+ , rv_fltR = delBndr (rv_fltR renv) x2 }
-- This rule does eta expansion
-- (\x.M) ~ N iff M ~ N x
-- 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 renv subst (Lam x1 e1) e2
+ = match renv' subst e1 (App e2 (varToCoreExpr new_x))
where
- (rn_env', new_x) = rnBndrL (me_env menv) x1
- menv' = menv { me_env = rn_env' }
+ (rn_env', new_x) = rnEtaL (rv_lcl renv) x1
+ renv' = renv { rv_lcl = 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 renv subst e1 (Lam x2 e2)
+ = match renv' 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)
- = do { subst1 <- match_ty menv subst ty1 ty2
- ; subst2 <- match 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
+ (rn_env', new_x) = rnEtaR (rv_lcl renv) x2
+ renv' = renv { rv_lcl = rn_env' }
+
+match renv subst (Case e1 x1 ty1 alts1) (Case e2 x2 ty2 alts2)
+ = do { subst1 <- match_ty renv subst ty1 ty2
+ ; subst2 <- match renv subst1 e1 e2
+ ; let renv' = rnMatchBndr2 renv subst x1 x2
+ ; match_alts renv' subst2 alts1 alts2 -- Alts are both sorted
}
-match menv subst (Type ty1) (Type ty2)
- = match_ty menv subst ty1 ty2
-
-match menv subst (Cast e1 co1) (Cast e2 co2)
- | (from1, to1) <- coercionKind co1
- , (from2, to2) <- coercionKind co2
- = do { subst1 <- match_ty menv subst to1 to2
- ; subst2 <- match_ty menv subst1 from1 from2
- ; match menv subst2 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 renv subst (Type ty1) (Type ty2)
+ = match_ty renv subst ty1 ty2
+match renv subst (Coercion co1) (Coercion co2)
+ = match_co renv subst co1 co2
+
+match renv subst (Cast e1 co1) (Cast e2 co2)
+ = do { subst1 <- match_co renv subst co1 co2
+ ; match renv subst1 e1 e2 }
-- Everything else fails
-match menv subst e1 e2 = -- pprTrace "Failing at" ((text "e1:" <+> ppr e1) $$ (text "e2:" <+> ppr e2)) $
- Nothing
+match _ _ _e1 _e2 = -- pprTrace "Failing at" ((text "e1:" <+> ppr _e1) $$ (text "e2:" <+> ppr _e2)) $
+ Nothing
+
+-------------
+match_co :: RuleEnv
+ -> RuleSubst
+ -> Coercion
+ -> Coercion
+ -> Maybe RuleSubst
+match_co renv subst (CoVarCo cv) co
+ = match_var renv subst cv (Coercion co)
+match_co _ _ co1 _
+ = pprTrace "match_co baling out" (ppr co1) Nothing
+
+-------------
+rnMatchBndr2 :: RuleEnv -> RuleSubst -> Var -> Var -> RuleEnv
+rnMatchBndr2 renv subst x1 x2
+ = renv { rv_lcl = rnBndr2 rn_env x1 x2
+ , rv_fltR = delBndr (rv_fltR renv) x2 }
+ where
+ rn_env = addRnInScopeSet (rv_lcl renv) (rs_bndrs subst)
+ -- Typically this is a no-op, but it may matter if
+ -- there are some floated let-bindings
------------------------------------------
-match_var :: MatchEnv
- -> SubstEnv
- -> Var -- Template
- -> CoreExpr -- Target
- -> Maybe SubstEnv
-match_var 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))
- -> Nothing -- Occurs check failure
- -- e.g. match forall a. (\x-> a x) against (\y. y y)
-
- | otherwise -- No renaming to do on e2
- -> Just (tv_subst, extendVarEnv id_subst v1' e2, binds)
+match_alts :: RuleEnv
+ -> RuleSubst
+ -> [CoreAlt] -- Template
+ -> [CoreAlt] -- Target
+ -> Maybe RuleSubst
+match_alts _ subst [] []
+ = return subst
+match_alts renv subst ((c1,vs1,r1):alts1) ((c2,vs2,r2):alts2)
+ | c1 == c2
+ = do { subst1 <- match renv' subst r1 r2
+ ; match_alts renv subst1 alts1 alts2 }
+ where
+ renv' = foldl mb renv (vs1 `zip` vs2)
+ mb renv (v1,v2) = rnMatchBndr2 renv subst v1 v2
- Just e2' | tcEqExprX (nukeRnEnvL rn_env) e2' e2
- -> Just subst
+match_alts _ _ _ _
+ = Nothing
- | otherwise
- -> Nothing
+------------------------------------------
+okToFloat :: RnEnv2 -> VarSet -> Bool
+okToFloat rn_env bind_fvs
+ = foldVarSet ((&&) . not_captured) True bind_fvs
+ where
+ not_captured fv = not (inRnEnvR rn_env fv)
- | otherwise -- v1 is not a template variable; check for an exact match with e2
- = case e2 of
- Var v2 | v1' == rnOccR rn_env v2 -> Just subst
- other -> Nothing
+------------------------------------------
+match_var :: RuleEnv
+ -> RuleSubst
+ -> Var -- Template
+ -> CoreExpr -- Target
+ -> Maybe RuleSubst
+match_var renv@(RV { rv_tmpls = tmpls, rv_lcl = rn_env, rv_fltR = flt_env })
+ subst v1 e2
+ | v1' `elemVarSet` tmpls
+ = match_tmpl_var renv subst v1' e2
+
+ | otherwise -- v1' is not a template variable; check for an exact match with e2
+ = case e2 of -- Remember, envR of rn_env is disjoint from rv_fltR
+ Var v2 | v1' == rnOccR rn_env v2
+ -> Just subst
+
+ | Var v2' <- lookupIdSubst (text "match_var") flt_env v2
+ , v1' == v2'
+ -> Just subst
+
+ _ -> Nothing
where
- rn_env = me_env menv
- v1' = rnOccL rn_env v1
+ v1' = rnOccL rn_env v1
-- If the template is
-- forall x. f x (\x -> x) = ...
-- Then the x inside the lambda isn't the
-- template x, so we must rename first!
-
------------------------------------------
-match_alts :: MatchEnv
- -> SubstEnv
- -> [CoreAlt] -- Template
- -> [CoreAlt] -- Target
- -> Maybe SubstEnv
-match_alts menv subst [] []
- = return subst
-match_alts 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 }
- where
- menv' :: MatchEnv
- menv' = menv { me_env = rnBndrs2 (me_env menv) vs1 vs2 }
+match_tmpl_var :: RuleEnv
+ -> RuleSubst
+ -> Var -- Template
+ -> CoreExpr -- Target
+ -> Maybe RuleSubst
+
+match_tmpl_var renv@(RV { rv_lcl = rn_env, rv_fltR = flt_env })
+ subst@(RS { rs_id_subst = id_subst, rs_bndrs = let_bndrs })
+ v1' e2
+ | any (inRnEnvR rn_env) (varSetElems (exprFreeVars e2))
+ = Nothing -- Occurs check failure
+ -- e.g. match forall a. (\x-> a x) against (\y. y y)
-match_alts menv subst alts1 alts2
- = Nothing
-\end{code}
+ | Just e1' <- lookupVarEnv id_subst v1'
+ = if eqExpr (rnInScopeSet rn_env) e1' e2'
+ then Just subst
+ else Nothing
-Matching Core types: use the matcher in TcType.
-Notice that we treat newtypes as opaque. For example, suppose
-we have a specialised version of a function at a newtype, say
- newtype T = MkT Int
-We only want to replace (f T) with f', not (f Int).
+ | otherwise
+ = -- Note [Matching variable types]
+ -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ -- However, we must match the *types*; e.g.
+ -- forall (c::Char->Int) (x::Char).
+ -- f (c x) = "RULE FIRED"
+ -- We must only match on args that have the right type
+ -- It's actually quite difficult to come up with an example that shows
+ -- you need type matching, esp since matching is left-to-right, so type
+ -- args get matched first. But it's possible (e.g. simplrun008) and
+ -- this is the Right Thing to do
+ do { subst' <- match_ty renv subst (idType v1') (exprType e2)
+ ; return (subst' { rs_id_subst = id_subst' }) }
+ where
+ -- e2' is the result of applying flt_env to e2
+ e2' | isEmptyVarSet let_bndrs = e2
+ | otherwise = substExpr (text "match_tmpl_var") flt_env e2
+
+ id_subst' = extendVarEnv (rs_id_subst subst) v1' e2'
+ -- No further renaming to do on e2',
+ -- because no free var of e2' is in the rnEnvR of the envt
-\begin{code}
------------------------------------------
-match_ty menv (tv_subst, id_subst, binds) ty1 ty2
- = do { tv_subst' <- Unify.ruleMatchTyX menv tv_subst ty1 ty2
- ; return (tv_subst', id_subst, binds) }
+match_ty :: RuleEnv
+ -> RuleSubst
+ -> Type -- Template
+ -> Type -- Target
+ -> Maybe RuleSubst
+-- Matching Core types: use the matcher in TcType.
+-- Notice that we treat newtypes as opaque. For example, suppose
+-- we have a specialised version of a function at a newtype, say
+-- newtype T = MkT Int
+-- We only want to replace (f T) with f', not (f Int).
+
+match_ty renv subst ty1 ty2
+ = do { tv_subst' <- Unify.ruleMatchTyX menv tv_subst ty1 ty2
+ ; return (subst { rs_tv_subst = tv_subst' }) }
+ where
+ tv_subst = rs_tv_subst subst
+ menv = ME { me_tmpls = rv_tmpls renv, me_env = rv_lcl renv }
\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 RuleSubst
+
+We can only do this if 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. Hence the
+use of okToFloat.
+
+There are a couple of tricky points.
+ (a) What if floating the binding captures a variable?
+ f (let v = x+1 in v) v
+ --> NOT!
+ let v = x+1 in f (x+1) v
+
+ (b) What if two non-nested let bindings bind the same variable?
+ f (let v = e1 in b1) (let v = e2 in b2)
+ --> NOT!
+ let v = e1 in let v = e2 in (f b2 b2)
+ See testsuite test "RuleFloatLet".
+
+Our cunning plan is this:
+ * Along with the growing substitution for template variables
+ we maintain a growing set of floated let-bindings (rs_binds)
+ plus the set of variables thus bound.
+
+ * The RnEnv2 in the MatchEnv binds only the local binders
+ in the term (lambdas, case)
+
+ * When we encounter a let in the term to be matched, we
+ check that does not mention any locally bound (lambda, case)
+ variables. If so we fail
+
+ * We use CoreSubst.substBind to freshen the binding, using an
+ in-scope set that is the original in-scope variables plus the
+ rs_bndrs (currently floated let-bindings). So in (a) above
+ we'll freshen the 'v' binding; in (b) above we'll freshen
+ the *second* 'v' binding.
+
+ * We apply that freshening substitution, in a lexically-scoped
+ way to the term, although lazily; this is the rv_fltR field.
+
+
+Note [Matching cases]
+~~~~~~~~~~~~~~~~~~~~~
+{- NOTE: This idea is currently disabled. It really only works if
+ the primops involved are OkForSpeculation, and, since
+ they have side effects readIntOfAddr and touch are not.
+ Maybe we'll get back to this later . -}
+
+Consider
+ f (case readIntOffAddr# p# i# realWorld# of { (# s#, n# #) ->
+ case touch# fp s# of { _ ->
+ I# n# } } )
+This happened in a tight loop generated by stream fusion that
+Roman encountered. We'd like to treat this just like the let
+case, because the primops concerned are ok-for-speculation.
+That is, we'd like to behave as if it had been
+ case readIntOffAddr# p# i# realWorld# of { (# s#, n# #) ->
+ case touch# fp s# of { _ ->
+ f (I# n# } } )
+
Note [Lookup in-scope]
~~~~~~~~~~~~~~~~~~~~~~
Consider this example
Data.Maybe.Nothing -> lvl_smf;
Data.Maybe.Just n_acT [Just S(L)] ->
case n_acT of wild1_ams [Just A] { GHC.Base.I# y_amr [Just L] ->
- $wfoo_smW (GHC.Prim.-# ds_Xmb y_amr) wild_Xf
+ \$wfoo_smW (GHC.Prim.-# ds_Xmb y_amr) wild_Xf
}};
and correctly generates the rule
RULES: "SC:$wfoo1" [0] __forall {y_amr [Just L] :: GHC.Prim.Int#
sc_snn :: GHC.Prim.Int#}
- $wfoo_smW sc_snn (Data.Maybe.Just @ GHC.Base.Int (GHC.Base.I# y_amr))
- = $s$wfoo_sno y_amr sc_snn ;]
+ \$wfoo_smW sc_snn (Data.Maybe.Just @ GHC.Base.Int (GHC.Base.I# y_amr))
+ = \$s\$wfoo_sno y_amr sc_snn ;]
BUT we must ensure that this rule matches in the original function!
-Note that the call to $wfoo is
- $wfoo_smW (GHC.Prim.-# ds_Xmb y_amr) wild_Xf
+Note that the call to \$wfoo is
+ \$wfoo_smW (GHC.Prim.-# ds_Xmb y_amr) wild_Xf
During matching we expand wild_Xf to (Just n_acT). But then we must also
expand n_acT to (I# y_amr). And we can only do that if we look up n_acT
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.
-
-NB: we assume that this follows a run of the simplifier, so every Id
-occurrence (including occurrences of imported Ids) is decorated with
-all its (active) rules. No need to construct a rule base or anything
-like that.
+ 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}
-ruleCheckProgram :: CompilerPhase -> String -> [CoreBind] -> SDoc
--- Report partial matches for rules beginning
--- with the specified string
-ruleCheckProgram phase rule_pat binds
+-- | Report partial matches for rules beginning with the specified
+-- string for the purposes of error reporting
+ruleCheckProgram :: CompilerPhase -- ^ Rule activation test
+ -> String -- ^ Rule pattern
+ -> RuleBase -- ^ Database of rules
+ -> [CoreBind] -- ^ Bindings to check in
+ -> SDoc -- ^ Resulting check message
+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 (phase, rule_pat)) 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 '-')
-type RuleCheckEnv = (CompilerPhase, String) -- Phase and Pattern
+data RuleCheckEnv = RuleCheckEnv {
+ rc_is_active :: Activation -> Bool,
+ rc_id_unf :: IdUnfoldingFun,
+ rc_pattern :: String,
+ rc_rule_base :: RuleBase
+}
ruleCheckBind :: RuleCheckEnv -> CoreBind -> Bag SDoc
-- The Bag returned has one SDoc for each call site found
-ruleCheckBind env (NonRec b r) = ruleCheck env r
-ruleCheckBind env (Rec prs) = unionManyBags [ruleCheck env r | (b,r) <- prs]
+ruleCheckBind env (NonRec _ r) = ruleCheck env r
+ruleCheckBind env (Rec prs) = unionManyBags [ruleCheck env r | (_,r) <- prs]
ruleCheck :: RuleCheckEnv -> CoreExpr -> Bag SDoc
-ruleCheck env (Var v) = emptyBag
-ruleCheck env (Lit l) = emptyBag
-ruleCheck env (Type ty) = emptyBag
+ruleCheck _ (Var _) = emptyBag
+ruleCheck _ (Lit _) = emptyBag
+ruleCheck _ (Type _) = emptyBag
+ruleCheck _ (Coercion _) = emptyBag
ruleCheck env (App f a) = ruleCheckApp env (App f a) []
-ruleCheck env (Note n e) = ruleCheck env e
-ruleCheck env (Cast e co) = ruleCheck env e
+ruleCheck env (Note _ e) = ruleCheck env e
+ruleCheck env (Cast e _) = ruleCheck env e
ruleCheck env (Let bd e) = ruleCheckBind env bd `unionBags` ruleCheck env e
-ruleCheck env (Lam b e) = ruleCheck env e
+ruleCheck env (Lam _ e) = ruleCheck env e
ruleCheck env (Case e _ _ as) = ruleCheck env e `unionBags`
unionManyBags [ruleCheck env r | (_,_,r) <- as]
+ruleCheckApp :: RuleCheckEnv -> Expr CoreBndr -> [Arg CoreBndr] -> Bag SDoc
ruleCheckApp env (App f a) as = ruleCheck env a `unionBags` ruleCheckApp env f (a:as)
ruleCheckApp env (Var f) as = ruleCheckFun env f as
-ruleCheckApp env other as = ruleCheck env other
+ruleCheckApp env other _ = ruleCheck env other
\end{code}
\begin{code}
-- Produce a report for all rules matching the predicate
-- saying why it doesn't match the specified application
-ruleCheckFun (phase, pat) fn args
+ruleCheckFun env fn args
| null name_match_rules = emptyBag
- | otherwise = unitBag (ruleAppCheck_help phase fn args name_match_rules)
+ | otherwise = unitBag (ruleAppCheck_help env fn args name_match_rules)
where
- name_match_rules = filter match (idCoreRules fn)
- match rule = pat `isPrefixOf` unpackFS (ruleName rule)
+ name_match_rules = filter match (getRules (rc_rule_base env) fn)
+ match rule = (rc_pattern env) `isPrefixOf` unpackFS (ruleName rule)
-ruleAppCheck_help :: CompilerPhase -> Id -> [CoreExpr] -> [CoreRule] -> SDoc
-ruleAppCheck_help phase 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)]
check_rule rule = rule_herald rule <> colon <+> rule_info rule
rule_herald (BuiltinRule { ru_name = name })
- = ptext SLIT("Builtin rule") <+> doubleQuotes (ftext name)
+ = ptext (sLit "Builtin rule") <+> doubleQuotes (ftext name)
rule_herald (Rule { ru_name = name })
- = ptext SLIT("Rule") <+> doubleQuotes (ftext name)
+ = 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_name = name, ru_act = act,
+ rule_info (Rule { ru_act = act,
ru_bndrs = rule_bndrs, ru_args = rule_args})
- | not (isActive phase 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 renv emptyRuleSubst rule_arg arg
where
- in_scope = lhs_fvs `unionVarSet` exprFreeVars arg
- menv = ME { me_env = mkRnEnv2 (mkInScopeSet in_scope)
- , me_tmpls = mkVarSet rule_bndrs }
+ in_scope = mkInScopeSet (lhs_fvs `unionVarSet` exprFreeVars arg)
+ renv = RV { rv_lcl = mkRnEnv2 in_scope
+ , rv_tmpls = mkVarSet rule_bndrs
+ , rv_fltR = mkEmptySubst in_scope
+ , rv_unf = rc_id_unf env }
\end{code}
projects / ghc-hetmet.git / blobdiff