X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Fspecialise%2FRules.lhs;h=26a499bfebc8a1f00c4264eb2f213d38043742de;hb=fa6c4bf01427a4191a595afecf90d96b27bad306;hp=92d3fbc22313c23f5fc65a30fbdc185b91b0989b;hpb=206b752961b48dcf8943632572b0a4f9c8a0fccc;p=ghc-hetmet.git

diff --git a/compiler/specialise/Rules.lhs b/compiler/specialise/Rules.lhs
index 92d3fbc..26a499b 100644
--- a/compiler/specialise/Rules.lhs
+++ b/compiler/specialise/Rules.lhs
@@ -20,7 +20,7 @@ module Rules (
 
 import CoreSyn		-- All of it
 import OccurAnal	( occurAnalyseExpr )
-import CoreFVs		( exprFreeVars, exprsFreeVars, bindFreeVars, rulesRhsFreeVars )
+import CoreFVs		( exprFreeVars, exprsFreeVars, bindFreeVars, rulesFreeVars )
 import CoreUnfold	( isCheapUnfolding, unfoldingTemplate )
 import CoreUtils	( tcEqExprX, exprType )
 import PprCore		( pprRules )
@@ -38,13 +38,14 @@ 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}
 
 
@@ -135,11 +136,11 @@ ruleCantMatch ts	     as		    = False
 
 \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) 
@@ -195,10 +196,27 @@ pprRuleBase rules = vcat [ pprRules (tidyRules emptyTidyEnv rs)
 %*									*
 %************************************************************************
 
+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
@@ -241,10 +259,15 @@ 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]) $
+  | 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