[project @ 2000-09-14 13:46:39 by simonpj]

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

diff --git a/ghc/compiler/stranal/WorkWrap.lhs b/ghc/compiler/stranal/WorkWrap.lhs
index 92eaf08..86f6437 100644 (file)
--- a/ghc/compiler/stranal/WorkWrap.lhs
+++ b/ghc/compiler/stranal/WorkWrap.lhs
@@ -10,25 +10,20 @@ module WorkWrap ( wwTopBinds, mkWrapper ) where
 
 import CoreSyn
 import CoreUnfold      ( Unfolding, certainlyWillInline )
-import CmdLineOpts     ( opt_UF_CreationThreshold , opt_D_verbose_core2core, 
-                          opt_D_dump_worker_wrapper
-                       )
+import CmdLineOpts     ( opt_D_verbose_core2core, opt_D_dump_worker_wrapper )
 import CoreLint                ( beginPass, endPass )
-import CoreUtils       ( exprType, exprArity, exprEtaExpandArity )
-import DataCon         ( DataCon )
+import CoreUtils       ( exprType, exprEtaExpandArity )
 import MkId            ( mkWorkerId )
-import Id              ( Id, idType, idStrictness, setIdArityInfo, isOneShotLambda,
+import Id              ( Id, idType, idStrictness, idArity, isOneShotLambda,
                          setIdStrictness, idInlinePragma, 
                          setIdWorkerInfo, idCprInfo, setInlinePragma )
-import VarSet
 import Type            ( Type, isNewType, splitForAllTys, splitFunTys )
 import IdInfo          ( mkStrictnessInfo, noStrictnessInfo, StrictnessInfo(..),
-                         CprInfo(..), exactArity, InlinePragInfo(..), WorkerInfo(..)
+                         CprInfo(..), exactArity, InlinePragInfo(..), isNeverInlinePrag,
+                         WorkerInfo(..)
                        )
 import Demand           ( Demand, wwLazy )
-import SaLib
 import UniqSupply      ( UniqSupply, initUs_, returnUs, thenUs, mapUs, getUniqueUs, UniqSM )
-import UniqSet
 import WwLib
 import Outputable
 \end{code}
@@ -189,14 +184,30 @@ tryWW     :: Bool                         -- True <=> a non-recursive binding
                                        -- if two, then a worker and a
                                        -- wrapper.
 tryWW non_rec fn_id rhs
-  | non_rec
-    && certainlyWillInline fn_id
-       -- No point in worker/wrappering something that is going to be
+  | isNeverInlinePrag inline_prag || arity == 0
+  =    -- Don't split things that will never be inlined
+    returnUs [ (fn_id, rhs) ]
+
+  | non_rec && not do_coerce_ww && certainlyWillInline fn_id
+       -- No point in worker/wrappering a function that is going to be
        -- INLINEd wholesale anyway.  If the strictness analyser is run
        -- twice, this test also prevents wrappers (which are INLINEd)
        -- from being re-done.
        --
+       -- The do_coerce_ww test is so that
+       -- a function with a coerce should w/w to get rid
+       -- of the coerces, which can significantly improve its arity.
+       -- Example:  f []     = return [] :: IO [Int]
+       --           f (x:xs) = return (x:xs)
+       -- If we aren't careful we end up with
+       --      f = \ x -> case x of {
+       --                   x:xs -> __coerce (IO [Int]) (\ s -> (# s, x:xs #)
+       --                   []   -> lvl_sJ8
+       --
+       --
        -- OUT OF DATE NOTE, kept for info:
+       -- It's out of date because now wrappers look very cheap 
+       -- even when they are inlined.
        --   In this case we add an INLINE pragma to the RHS.  Why?
        --   Because consider
        --        f = \x -> g x x
@@ -204,8 +215,6 @@ tryWW non_rec fn_id rhs
        --   Then f is small, so we don't w/w it.  But g is big, and we do, so
        --   g's wrapper will get inlined in f's RHS, which makes f look big now.
        --   So f doesn't get inlined, but it is strict and we have failed to w/w it.
-       -- It's out of date because now wrappers look very cheap 
-       -- even when they are inlined.
   = returnUs [ (fn_id, rhs) ]
 
   | not (do_strict_ww || do_cpr_ww || do_coerce_ww)
@@ -222,13 +231,9 @@ tryWW non_rec fn_id rhs
        work_id | has_strictness = proto_work_id `setIdStrictness` mkStrictnessInfo (work_demands, result_bot)
                | otherwise      = proto_work_id
 
-       wrap_arity = exprArity wrap_rhs         -- Might be greater than the current visible arity
-                                               -- if the function returns bottom
-                                               
        wrap_rhs = wrap_fn work_id
        wrap_id  = fn_id `setIdStrictness`      wrapper_strictness
-                         `setIdWorkerInfo`     HasWorker work_id wrap_arity
-                        `setIdArityInfo`       exactArity wrap_arity
+                         `setIdWorkerInfo`     HasWorker work_id arity
                         `setInlinePragma`      NoInlinePragInfo        -- Put it on the worker instead
                -- Add info to the wrapper:
                --      (a) we want to set its arity
@@ -237,12 +242,12 @@ tryWW non_rec fn_id rhs
     in
     returnUs ([(work_id, work_rhs), (wrap_id, wrap_rhs)])
        -- Worker first, because wrapper mentions it
-       -- Arrange to inline the wrapper unconditionally
+       -- mkWwBodies has already built a wrap_rhs with an INLINE pragma wrapped around it
   where
     fun_ty = idType fn_id
-    arity  = exprEtaExpandArity rhs
+    arity  = idArity fn_id     -- The arity is set by the simplifier using exprEtaExpandArity
+                               -- So it may be more than the number of top-level-visible lambdas
 
-       -- Don't split something which is marked unconditionally NOINLINE
     inline_prag  = idInlinePragma fn_id
 
     strictness_info           = idStrictness fn_id