Improvement to SimplUtils.mkLam

[ghc-hetmet.git] / compiler / simplCore / SimplUtils.lhs

diff --git a/compiler/simplCore/SimplUtils.lhs b/compiler/simplCore/SimplUtils.lhs
index 500f286..96857a3 100644 (file)
--- a/compiler/simplCore/SimplUtils.lhs
+++ b/compiler/simplCore/SimplUtils.lhs
@@ -475,9 +475,9 @@ On the other hand, it is bad not to do ANY inlining into an
 InlineRule, because then recursive knots in instance declarations
 don't get unravelled.
 
-However, *sometimes* SimplGently must do no call-site inlining at all.
-Before full laziness we must be careful not to inline wrappers,
-because doing so inhibits floating
+However, *sometimes* SimplGently must do no call-site inlining at all
+(hence sm_inline = False).  Before full laziness we must be careful
+not to inline wrappers, because doing so inhibits floating
     e.g. ...(case f x of ...)...
     ==> ...(case (case x of I# x# -> fw x#) of ...)...
     ==> ...(case x of I# x# -> case fw x# of ...)...
@@ -502,6 +502,9 @@ RULES are enabled when doing "gentle" simplification.  Two reasons:
     to work in Template Haskell when simplifying
     splices, so we get simpler code for literal strings
 
+But watch out: list fusion can prevent floating.  So use phase control
+to switch off those rules until after floating.
+
 Note [Simplifying inside InlineRules]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 We must take care with simplification inside InlineRules (which come from
@@ -1010,7 +1013,7 @@ mkLam :: SimplEnv -> [OutBndr] -> OutExpr -> SimplM OutExpr
 
 mkLam _b [] body 
   = return body
-mkLam env bndrs body
+mkLam _env bndrs body
   = do { dflags <- getDOptsSmpl
        ; mkLam' dflags bndrs body }
   where
@@ -1024,6 +1027,11 @@ mkLam env bndrs body
        co_vars  = tyVarsOfType co
        bad bndr = isCoVar bndr && bndr `elemVarSet` co_vars      
 
+    mkLam' dflags bndrs body@(Lam {})
+      = mkLam' dflags (bndrs ++ bndrs1) body1
+      where
+        (bndrs1, body1) = collectBinders body
+
     mkLam' dflags bndrs body
       | dopt Opt_DoEtaReduction dflags,
         Just etad_lam <- tryEtaReduce bndrs body
@@ -1031,9 +1039,6 @@ mkLam env bndrs body
           ; return etad_lam }
 
       | dopt Opt_DoLambdaEtaExpansion dflags,
-        not (inGentleMode env),              -- In gentle mode don't eta-expansion
-                                     -- because it can clutter up the code
-                                     -- with casts etc that may not be removed
        not (all isTyVar bndrs) -- Don't eta expand type abstractions
       = do { let body' = tryEtaExpansion dflags body
           ; return (mkLams bndrs body') }