X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2FsimplCore%2FSimplify.lhs;h=d2e912b900d6471a74c11407e4d9f61d98993ee8;hb=e50fa4a41693ccd5d95034d02f4452b6c627a377;hp=efd1b780b0e574eeb76248145ced3af38982ed6c;hpb=34ed7e85106d75a3e723d248c98b35df134f5022;p=ghc-hetmet.git

diff --git a/compiler/simplCore/Simplify.lhs b/compiler/simplCore/Simplify.lhs
index efd1b78..d2e912b 100644
--- a/compiler/simplCore/Simplify.lhs
+++ b/compiler/simplCore/Simplify.lhs
@@ -410,7 +410,7 @@ becomes
 prepareRhs :: SimplEnv -> OutExpr -> SimplM (SimplEnv, OutExpr)
 -- Adds new floats to the env iff that allows us to return a good RHS
 
-prepareRhs env (Cast rhs co)	-- Note [Float coersions]
+prepareRhs env (Cast rhs co)	-- Note [Float coercions]
   = do	{ (env', rhs') <- makeTrivial env rhs
 	; return (env', Cast rhs' co) }
 
@@ -735,8 +735,9 @@ simplCast env body co cont
   where
        addCoerce co cont = add_coerce co (coercionKind co) cont
 
-       add_coerce co (s1, k1) cont 
-         | s1 `coreEqType` k1 = cont
+       add_coerce co (s1, k1) cont 	-- co :: ty~ty
+         | s1 `coreEqType` k1 = cont	-- is a no-op
+
        add_coerce co1 (s1, k2) (CoerceIt co2 cont)
          | (l1, t1) <- coercionKind co2
                 -- 	coerce T1 S1 (coerce S1 K1 e)
@@ -1123,18 +1124,10 @@ in action in spectral/cichelli/Prog.hs:
 	 [(m,n) | m <- [1..max], n <- [1..max]]
 Hence the check for NoCaseOfCase.
 
-Note [Case of cast]
-~~~~~~~~~~~~~~~~~~~
-Consider 	case (v `cast` co) of x { I# ->
-		... (case (v `cast` co) of {...}) ...
-We'd like to eliminate the inner case.  We can get this neatly by 
-arranging that inside the outer case we add the unfolding
-	v |-> x `cast` (sym co)
-to v.  Then we should inline v at the inner case, cancel the casts, and away we go
-	
-Note 2
-~~~~~~
-There is another situation when we don't want to do it.  If we have
+Note [Suppressing the case binder-swap]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+There is another situation when it might make sense to suppress the
+case-expression binde-swap. If we have
 
     case x of w1 { DEFAULT -> case x of w2 { A -> e1; B -> e2 }
 	           ...other cases .... }
@@ -1196,6 +1189,15 @@ The point is that we bring into the envt a binding
 after the outer case, and that makes (a,b) alive.  At least we do unless
 the case binder is guaranteed dead.
 
+Note [Case of cast]
+~~~~~~~~~~~~~~~~~~~
+Consider 	case (v `cast` co) of x { I# ->
+		... (case (v `cast` co) of {...}) ...
+We'd like to eliminate the inner case.  We can get this neatly by 
+arranging that inside the outer case we add the unfolding
+	v |-> x `cast` (sym co)
+to v.  Then we should inline v at the inner case, cancel the casts, and away we go
+	
 \begin{code}
 simplCaseBinder :: SimplEnv -> OutExpr -> InId -> SimplM (SimplEnv, OutId)
 simplCaseBinder env scrut case_bndr