Do not perform a worker/wrapper split for a NOINLINE function

This came up in an email exchange with Duncan Coutts in May 2007.
If a function is marked NOINLINE there is really no point in
doing a worker/wrapper split, because the wrapper will never
be inlined.

diff --git a/compiler/stranal/WorkWrap.lhs b/compiler/stranal/WorkWrap.lhs
index d061de5..a1b18a9 100644 (file)
--- a/compiler/stranal/WorkWrap.lhs
+++ b/compiler/stranal/WorkWrap.lhs
@@ -26,7 +26,7 @@ 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 +215,11 @@ 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