Return results of Cmm streams in backends

This generalizes code generators (outputAsm, outputLlvm, outputC, and
the call site codeOutput) so that they'll return the return values of
the passed Cmm streams.

This allows accumulating data during Cmm generation and returning it to
the call site in HscMain.

Previously the Cmm streams were assumed to return (), so the code
generators returned () as well.

This change is required by !1304 and !1530.

Skipping CI as this was tested before and I only updated the commit
message.

[skip ci]

1 files changed, 5 insertions, 4 deletions

diff --git a/compiler/cmm/CmmInfo.hs b/compiler/cmm/CmmInfo.hs
index 138e7aa8d8..60814f8039 100644
--- a/compiler/cmm/CmmInfo.hs
+++ b/compiler/cmm/CmmInfo.hs
@@ -67,16 +67,17 @@ mkEmptyContInfoTable info_lbl
                  , cit_srt  = Nothing
                  , cit_clo  = Nothing }
 
-cmmToRawCmm :: DynFlags -> Stream IO CmmGroup ()
-            -> IO (Stream IO RawCmmGroup ())
+cmmToRawCmm :: DynFlags -> Stream IO CmmGroup a
+            -> IO (Stream IO RawCmmGroup a)
 cmmToRawCmm dflags cmms
   = do { uniqs <- mkSplitUniqSupply 'i'
-       ; let do_one uniqs cmm =
+       ; let do_one :: UniqSupply -> [CmmDecl] -> IO (UniqSupply, [RawCmmDecl])
+             do_one uniqs cmm =
                -- NB. strictness fixes a space leak.  DO NOT REMOVE.
                withTiming (return dflags) (text "Cmm -> Raw Cmm") forceRes $
                  case initUs uniqs $ concatMapM (mkInfoTable dflags) cmm of
                    (b,uniqs') -> return (uniqs',b)
-       ; return (Stream.mapAccumL do_one uniqs cmms >> return ())
+       ; return (snd <$> Stream.mapAccumL_ do_one uniqs cmms)
        }
 
     where forceRes (uniqs, rawcmms) =