\section[CoreRules]{Transformation rules}
\begin{code}
+{-# OPTIONS -w #-}
+-- The above warning supression flag is a temporary kludge.
+-- While working on this module you are encouraged to remove it and fix
+-- any warnings in the module. See
+-- http://hackage.haskell.org/trac/ghc/wiki/CodingStyle#Warnings
+-- for details
+
module Rules (
RuleBase, emptyRuleBase, mkRuleBase, extendRuleBaseList,
unionRuleBase, pprRuleBase, ruleCheckProgram,
#include "HsVersions.h"
import CoreSyn -- All of it
-import CoreSubst ( substExpr, mkSubst )
import OccurAnal ( occurAnalyseExpr )
-import CoreFVs ( exprFreeVars, exprsFreeVars, bindFreeVars, rulesRhsFreeVars )
+import CoreFVs ( exprFreeVars, exprsFreeVars, bindFreeVars, rulesFreeVars )
import CoreUnfold ( isCheapUnfolding, unfoldingTemplate )
-import CoreUtils ( tcEqExprX )
+import CoreUtils ( tcEqExprX, exprType )
import PprCore ( pprRules )
-import Type ( TvSubstEnv )
+import Type ( Type, TvSubstEnv )
import Coercion ( coercionKind )
import TcType ( tcSplitTyConApp_maybe )
import CoreTidy ( tidyRules )
-import Id ( Id, idUnfolding, isLocalId, isGlobalId, idName,
+import Id ( Id, idUnfolding, isLocalId, isGlobalId, idName, idType,
idSpecialisation, idCoreRules, setIdSpecialisation )
import IdInfo ( SpecInfo( SpecInfo ) )
import Var ( Var )
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}
\begin{code}
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)
%* *
%************************************************************************
+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
+
\begin{code}
lookupRule :: (Activation -> Bool) -> InScopeSet
-> RuleBase -- Imported rules
-> Id -> [CoreExpr] -> Maybe (CoreRule, CoreExpr)
+-- See Note [Extra argsin rule matching]
lookupRule is_active in_scope rule_base fn args
= matchRules is_active in_scope fn args rules
where
| 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]) $
+ | otherwise = 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
where
rn_env = me_env menv
bndrs = bindersOf bind
- rhss = rhssOfBind bind
bind_fvs = varSetElems (bindFreeVars bind)
locally_bound x = inRnEnvR rn_env x
freshly_bound x = not (x `rnInScope` rn_env)
-> 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)
+ | otherwise -- No renaming to do on e2, because no free var
+ -- of e2 is in the rnEnvR of the envt
+ -- 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 { tv_subst' <- Unify.ruleMatchTyX menv tv_subst (idType v1') (exprType e2)
+ -- c.f. match_ty below
+ ; return (tv_subst', extendVarEnv id_subst v1' e2, binds) }
Just e1' | tcEqExprX (nukeRnEnvL rn_env) e1' e2
-> Just subst
\begin{code}
------------------------------------------
+match_ty :: MatchEnv
+ -> SubstEnv
+ -> Type -- Template
+ -> Type -- Target
+ -> Maybe SubstEnv
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) }
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