Fix a long-standing bug in FloatOut

We really should not float anything out of an _inline_me_ Note,
for reasons described in this new comment:
	-- Do no floating at all inside INLINE.
	-- The SetLevels pass did not clone the bindings, so it's
	-- unsafe to do any floating, even if we dump the results
	-- inside the Note (which is what we used to do).

I'm about to get rid of these _inline_me_ Notes, but it's
better to fix it anyway.  I found this bug when implementing System IF.

diff --git a/compiler/simplCore/FloatOut.lhs b/compiler/simplCore/FloatOut.lhs
index 4179774..bbf6f0a 100644 (file)
--- a/compiler/simplCore/FloatOut.lhs
+++ b/compiler/simplCore/FloatOut.lhs
@@ -316,15 +316,11 @@ floatExpr lvl (Note note@(SCC cc) expr)
          = Rec [(binder, mkSCC dupd_cc rhs) | (binder, rhs) <- pairs]
 
 floatExpr lvl (Note InlineMe expr)     -- Other than SCCs
-  = case floatExpr InlineCtxt expr of { (fs, floating_defns, expr') ->
-       -- There can be some floating_defns, arising from
-       -- ordinary lets that were there all the time.  It seems
-       -- more efficient to test once here than to avoid putting
-       -- them into floating_defns (which would mean testing for
-       -- inlineCtxt  at every let)
-    (fs, [], Note InlineMe (install floating_defns expr')) }
-       -- See Note [FloatOut inside INLINE] in SetLevels
-       -- I'm guessing that floating_dens should be empty
+  = (zeroStats, [], Note InlineMe (unTag expr))
+       -- Do no floating at all inside INLINE. [_$_]
+       -- The SetLevels pass did not clone the bindings, so it's
+       -- unsafe to do any floating, even if we dump the results
+       -- inside the Note (which is what we used to do).
 
 floatExpr lvl (Note note expr) -- Other than SCCs
   = case (floatExpr lvl expr)    of { (fs, floating_defns, expr') ->
@@ -366,6 +362,22 @@ floatList f [] = (zeroStats, [], [])
 floatList f (a:as) = case f a           of { (fs_a,  binds_a,  b)  ->
                     case floatList f as of { (fs_as, binds_as, bs) ->
                     (fs_a `add_stats` fs_as, binds_a ++ binds_as, b:bs) }}
+
+unTagBndr :: TaggedBndr tag -> CoreBndr
+unTagBndr (TB b _) = b
+
+unTag :: TaggedExpr tag -> CoreExpr
+unTag (Var v)            = Var v
+unTag (Lit l)            = Lit l
+unTag (Type ty)   = Type ty
+unTag (Note n e)  = Note n (unTag e)
+unTag (App e1 e2) = App (unTag e1) (unTag e2)
+unTag (Lam b e)   = Lam (unTagBndr b) (unTag e)
+unTag (Cast e co) = Cast (unTag e) co
+unTag (Let (Rec prs) e)    = Let (Rec [(unTagBndr b,unTag r) | (b, r) <- prs]) (unTag e)
+unTag (Let (NonRec b r) e) = Let (NonRec (unTagBndr b) (unTag r)) (unTag e)
+unTag (Case e b ty alts)   = Case (unTag e) (unTagBndr b) ty
+                                 [(c, map unTagBndr bs, unTag r) | (c,bs,r) <- alts]
 \end{code}
 
 %************************************************************************