[project @ 2001-02-21 11:04:17 by simonpj]

Be a bit more careful in CoreSat.deLam

diff --git a/ghc/compiler/coreSyn/CoreSat.lhs b/ghc/compiler/coreSyn/CoreSat.lhs
index 62eda2e..c993d48 100644 (file)
--- a/ghc/compiler/coreSyn/CoreSat.lhs
+++ b/ghc/compiler/coreSyn/CoreSat.lhs
@@ -41,6 +41,7 @@ MAJOR CONSTRAINT:
 
        So we must not change the arity of any top-level function,
        because we've already fixed it and put it out into the interface file.
+       Nor must we change a value (e.g. constructor) into a thunk.
 
        It's ok to introduce extra bindings, which don't appear in the
        interface file.  We don't put arity info on these extra bindings,
@@ -418,6 +419,13 @@ mkBinds binds body
 
 deLam :: CoreExpr -> UniqSM CoreExpr   
 -- Remove top level lambdas by let-bindinig
+
+deLam (Note n expr)
+  =    -- You can get things like
+       --      case e of { p -> coerce t (\s -> ...) }
+    deLam expr `thenUs` \ expr' ->
+    returnUs (Note n expr')
+
 deLam expr 
   | null bndrs = returnUs expr
   | otherwise  = case tryEta bndrs body of
@@ -427,6 +435,11 @@ deLam expr
   where
     (bndrs,body) = collectBinders expr
 
+-- Why try eta reduction?  Hasn't the simplifier already done eta?
+-- But the simplifier only eta reduces if that leaves something
+-- trivial (like f, or f Int).  But for deLam it would be enough to
+-- get to a partial application, like (map f).
+
 tryEta bndrs expr@(App _ _)
   | ok_to_eta_reduce f &&
     n_remaining >= 0 &&
@@ -496,3 +509,5 @@ safeDem, onceDem :: RhsDemand
 safeDem = RhsDemand False False  -- always safe to use this
 onceDem = RhsDemand False True   -- used at most once
 \end{code}
+
+