[project @ 2002-11-11 10:58:40 by simonpj]

------------------
  	Improve byte-code compilation of unboxed
	 	tuple returns
		------------------

The previous byte-code for returning unboxed tuples was just wrong.  It's
a special case for the situation where we return (# s, x #), where s is
a state token, so we can just return the single result 'x' on top of the
stack.  Previously we generated an ENTER at the end, which is plain wrong.
We should RETURN.

It still doesn't work, for other tiresome reasons...but rather than fix it
we'll wait for eval-apply.  Meanwhile it's less wrong than before.

diff --git a/ghc/compiler/ghci/ByteCodeGen.lhs b/ghc/compiler/ghci/ByteCodeGen.lhs
index 72f4d62..0d21f2d 100644 (file)
--- a/ghc/compiler/ghci/ByteCodeGen.lhs
+++ b/ghc/compiler/ghci/ByteCodeGen.lhs
@@ -648,18 +648,25 @@ schemeT d s p app
      )
 
    -- Case 2
-   | [arg1,arg2] <- args_r_to_l,
+   | is_con_call,
+     isUnboxedTupleCon con,                    -- (# ... #)
+     [(_,arg1),(_,arg2)] <- args_r_to_l,       -- Exactly two args
      let 
-        isVoidRepAtom (_, AnnVar v)    = typePrimRep (idType v) == VoidRep
-         isVoidRepAtom (_, AnnNote n e) = isVoidRepAtom e
-        isVoidRepAtom _ = False
+        isVoidRepAtom (AnnVar v)        = typePrimRep (idType v) == VoidRep
+         isVoidRepAtom (AnnNote n (_,e)) = isVoidRepAtom e
+        isVoidRepAtom _                 = False
      in  
-        isVoidRepAtom arg2
+     isVoidRepAtom arg2                        -- The first arg is void
    = --trace (if isSingleton args_r_to_l
      --       then "schemeT: unboxed singleton"
      --       else "schemeT: unboxed pair with Void first component") (
-     schemeT d s p arg1
-     --)
+     pushAtom True d p arg1    `thenBc` \ (push, szw) ->
+     returnBc (push                            -- value onto stack
+               `appOL`  mkSLIDE szw (d-s)      -- clear to sequel
+               `snocOL` RETURN (atomRep arg1)) -- go
+       -- We used to use "schemeT d s p arg1", but that is wrong.
+       -- We must use RETURN (because it's an unboxed tuple)
+       -- I think that this still does not work: SLPJ Oct 02
 
    -- Case 3
    | Just (CCall ccall_spec) <- isFCallId_maybe fn