Remove debug warning, and explain why

[ghc-hetmet.git] / compiler / stranal / WorkWrap.lhs

diff --git a/compiler/stranal/WorkWrap.lhs b/compiler/stranal/WorkWrap.lhs
index d061de5..3667da8 100644 (file)
--- a/compiler/stranal/WorkWrap.lhs
+++ b/compiler/stranal/WorkWrap.lhs
@@ -4,6 +4,13 @@
 \section[WorkWrap]{Worker/wrapper-generating back-end of strictness analyser}
 
 \begin{code}
+{-# OPTIONS -w #-}
+-- The above warning supression flag is a temporary kludge.
+-- While working on this module you are encouraged to remove it and fix
+-- any warnings in the module. See
+--     http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
+-- for details
+
 module WorkWrap ( wwTopBinds, mkWrapper ) where
 
 #include "HsVersions.h"
@@ -26,7 +33,7 @@ import NewDemand        ( Demand(..), StrictSig(..), DmdType(..), DmdResult(..),
                        )
 import UniqSupply      ( UniqSupply, initUs_, returnUs, thenUs, mapUs, getUniqueUs, UniqSM )
 import Unique          ( hasKey )
-import BasicTypes      ( RecFlag(..), isNonRec )
+import BasicTypes      ( RecFlag(..), isNonRec, isNeverActive )
 import VarEnv          ( isEmptyVarEnv )
 import Maybes          ( orElse )
 import DynFlags
@@ -215,6 +222,11 @@ tryWW is_rec fn_id rhs
        --      fw = \ab -> (__inline (\x -> E)) (a,b)
        -- and the original __inline now vanishes, so E is no longer
        -- inside its __inline wrapper.  Death!  Disaster!
+
+  || isNeverActive inline_prag
+       -- No point in worker/wrappering if the thing is never inlined!
+       -- Because the no-inline prag will prevent the wrapper ever
+       -- being inlined at a call site. 
   = returnUs [ (new_fn_id, rhs) ]
 
   | is_thunk && worthSplittingThunk maybe_fn_dmd res_info
@@ -364,17 +376,7 @@ worthSplittingFun ds res
   = any worth_it ds || returnsCPR res
        -- worthSplitting returns False for an empty list of demands,
        -- and hence do_strict_ww is False if arity is zero and there is no CPR
-
-       -- We used not to split if the result is bottom.
-       -- [Justification:  there's no efficiency to be gained.]
-       -- But it's sometimes bad not to make a wrapper.  Consider
-       --      fw = \x# -> let x = I# x# in case e of
-       --                                      p1 -> error_fn x
-       --                                      p2 -> error_fn x
-       --                                      p3 -> the real stuff
-       -- The re-boxing code won't go away unless error_fn gets a wrapper too.
-       -- [We don't do reboxing now, but in general it's better to pass 
-       --  an unboxed thing to f, and have it reboxed in the error cases....]
+  -- See Note [Worker-wrapper for bottoming functions]
   where
     worth_it Abs             = True    -- Absent arg
     worth_it (Eval (Prod ds)) = True   -- Product arg to evaluate
@@ -391,6 +393,19 @@ worthSplittingThunk maybe_dmd res
     worth_it other                  = False
 \end{code}
 
+Note [Worker-wrapper for bottoming functions]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+We used not to split if the result is bottom.
+[Justification:  there's no efficiency to be gained.]
+
+But it's sometimes bad not to make a wrapper.  Consider
+       fw = \x# -> let x = I# x# in case e of
+                                       p1 -> error_fn x
+                                       p2 -> error_fn x
+                                       p3 -> the real stuff
+The re-boxing code won't go away unless error_fn gets a wrapper too.
+[We don't do reboxing now, but in general it's better to pass an
+unboxed thing to f, and have it reboxed in the error cases....]
 
 
 %************************************************************************