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

[ghc-hetmet.git] / ghc / compiler / coreSyn / CoreSat.lhs

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.
 
        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,
 
        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 :: 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
 deLam expr 
   | null bndrs = returnUs expr
   | otherwise  = case tryEta bndrs body of

@@ -427,6 +435,11 @@ deLam expr
   where
     (bndrs,body) = collectBinders 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 &&
 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}
 safeDem = RhsDemand False False  -- always safe to use this
 onceDem = RhsDemand False True   -- used at most once
 \end{code}

+
+