From: simonpj <unknown>
Date: Mon, 2 Sep 2002 16:39:19 +0000 (+0000)
Subject: [project @ 2002-09-02 16:39:19 by simonpj]
X-Git-Tag: Approx_11550_changesets_converted~1731
X-Git-Url: http://git.megacz.com/?a=commitdiff_plain;h=3a9075020fbffec15481ae06c84a96c5fd9a808d;p=ghc-hetmet.git

[project @ 2002-09-02 16:39:19 by simonpj]
Wibble in demand analyser; no need to merge
---

diff --git a/ghc/compiler/stranal/DmdAnal.lhs b/ghc/compiler/stranal/DmdAnal.lhs
index 5320305..c42099d 100644
--- a/ghc/compiler/stranal/DmdAnal.lhs
+++ b/ghc/compiler/stranal/DmdAnal.lhs
@@ -334,19 +334,27 @@ dmdFix top_lvl sigs orig_pairs
 	 -> [(Id,CoreExpr)] 		
 	 -> (SigEnv, DmdEnv, [(Id,CoreExpr)])
     loop n sigs pairs
-      | all (same_sig sigs sigs') bndrs 
+      | found_fixpoint
       = (sigs', lazy_fv, pairs')
 		-- Note: use pairs', not pairs.   pairs' is the result of 
 		-- processing the RHSs with sigs (= sigs'), whereas pairs 
 		-- is the result of processing the RHSs with the *previous* 
 		-- iteration of sigs.
-      | n >= 10       = pprTrace "dmdFix loop" (ppr n <+> (vcat 
+
+      | n >= 10  = pprTrace "dmdFix loop" (ppr n <+> (vcat 
 				[ text "Sigs:" <+> ppr [(id,lookup sigs id, lookup sigs' id) | (id,_) <- pairs],
 				  text "env:" <+> ppr (ufmToList sigs),
 				  text "binds:" <+> pprCoreBinding (Rec pairs)]))
-			      (emptySigEnv, emptyDmdEnv, orig_pairs)	-- Safe output
+			      (emptySigEnv, lazy_fv, orig_pairs)	-- Safe output
+			-- The lazy_fv part is really important!  orig_pairs has no strictness
+			-- info, including nothing about free vars.  But if we have
+			--	letrec f = ....y..... in ...f...
+			-- where 'y' is free in f, we must record that y is mentioned, 
+			-- otherwise y will get recorded as absent altogether
+
       | otherwise    = loop (n+1) sigs' pairs'
       where
+	found_fixpoint = all (same_sig sigs sigs') bndrs 
 		-- Use the new signature to do the next pair
 		-- The occurrence analyser has arranged them in a good order
 		-- so this can significantly reduce the number of iterations needed