[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 (file)
--- 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