module WorkWrap ( wwTopBinds, mkWrapper ) where

import CoreSyn
import CoreUnfold	( certainlyWillInline, mkInlineUnfolding, mkWwInlineRule )
import CoreUtils	( exprType, exprIsHNF )
import CoreArity	( exprArity )
import Var
import Id
import Type		( Type )
import IdInfo
import Demand
import UniqSupply
import BasicTypes
import VarEnv		( isEmptyVarEnv )
import Maybes		( orElse )
import WwLib
import Util		( lengthIs, notNull )
import Outputable
import MonadUtils

#include "HsVersions.h"

wwTopBinds :: UniqSupply -> [CoreBind] -> [CoreBind]

wwTopBinds us top_binds
  = initUs_ us $ do
    top_binds' <- mapM wwBind top_binds
    return (concat top_binds')

wwBind	:: CoreBind
	-> UniqSM [CoreBind]	-- returns a WwBinding intermediate form;
				-- the caller will convert to Expr/Binding,
				-- as appropriate.

wwBind (NonRec binder rhs) = do
    new_rhs <- wwExpr rhs
    new_pairs <- tryWW NonRecursive binder new_rhs
    return [NonRec b e | (b,e) <- new_pairs]
      -- Generated bindings must be non-recursive
      -- because the original binding was.

wwBind (Rec pairs)
  = return . Rec <$> concatMapM do_one pairs
  where
    do_one (binder, rhs) = do new_rhs <- wwExpr rhs
                              tryWW Recursive binder new_rhs

wwExpr :: CoreExpr -> UniqSM CoreExpr

wwExpr e@(Type {}) = return e
wwExpr e@(Coercion {}) = return e
wwExpr e@(Lit  {}) = return e
wwExpr e@(Var  {}) = return e

wwExpr (Lam binder expr)
  = Lam binder <$> wwExpr expr

wwExpr (App f a)
  = App <$> wwExpr f <*> wwExpr a

wwExpr (Note note expr)
  = Note note <$> wwExpr expr

wwExpr (Cast expr co) = do
    new_expr <- wwExpr expr
    return (Cast new_expr co)

wwExpr (Let bind expr)
  = mkLets <$> wwBind bind <*> wwExpr expr

wwExpr (Case expr binder ty alts) = do
    new_expr <- wwExpr expr
    new_alts <- mapM ww_alt alts
    return (Case new_expr binder ty new_alts)
  where
    ww_alt (con, binders, rhs) = do
        new_rhs <- wwExpr rhs
        return (con, binders, new_rhs)

tryWW	:: RecFlag
	-> Id				-- The fn binder
	-> CoreExpr			-- The bound rhs; its innards
					--   are already ww'd
	-> UniqSM [(Id, CoreExpr)]	-- either *one* or *two* pairs;
					-- if one, then no worker (only
					-- the orig "wrapper" lives on);
					-- if two, then a worker and a
					-- wrapper.
tryWW is_rec fn_id rhs
  | isNeverActive inline_act
	-- 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. 
	-- 
	-- Furthermore, don't even expose strictness info
  = return [ (fn_id, rhs) ]

  | is_thunk && worthSplittingThunk maybe_fn_dmd res_info
  	-- See Note [Thunk splitting]
  = ASSERT2( isNonRec is_rec, ppr new_fn_id )	-- The thunk must be non-recursive
    checkSize new_fn_id rhs $ 
    splitThunk new_fn_id rhs

  | is_fun && worthSplittingFun wrap_dmds res_info
  = checkSize new_fn_id rhs $
    splitFun new_fn_id fn_info wrap_dmds res_info rhs

  | otherwise
  = return [ (new_fn_id, rhs) ]

  where
    fn_info   	 = idInfo fn_id
    maybe_fn_dmd = demandInfo fn_info
    inline_act   = inlinePragmaActivation (inlinePragInfo fn_info)

	-- In practice it always will have a strictness 
	-- signature, even if it's a uninformative one
    strict_sig  = strictnessInfo fn_info `orElse` topSig
    StrictSig (DmdType env wrap_dmds res_info) = strict_sig

	-- new_fn_id has the DmdEnv zapped.  
	--	(a) it is never used again
	--	(b) it wastes space
	--	(c) it becomes incorrect as things are cloned, because
	--	    we don't push the substitution into it
    new_fn_id | isEmptyVarEnv env = fn_id
	      | otherwise	  = fn_id `setIdStrictness` 
				     StrictSig (mkTopDmdType wrap_dmds res_info)

    is_fun    = notNull wrap_dmds
    is_thunk  = not is_fun && not (exprIsHNF rhs)

---------------------
checkSize :: Id -> CoreExpr
	  -> UniqSM [(Id,CoreExpr)] -> UniqSM [(Id,CoreExpr)]
checkSize fn_id rhs thing_inside
  | isStableUnfolding (realIdUnfolding fn_id)
  = return [ (fn_id, rhs) ]
      -- See Note [Don't w/w INLINABLE things]
      -- and Note [Don't w/w INLINABLABLE things]
      -- NB: use realIdUnfolding because we want to see the unfolding
      --     even if it's a loop breaker!

  | certainlyWillInline (idUnfolding fn_id)
  = return [ (fn_id `setIdUnfolding` inline_rule, rhs) ]
	-- Note [Don't w/w inline small non-loop-breaker things]
	-- NB: use idUnfolding because we don't want to apply
	--     this criterion to a loop breaker!

  | otherwise = thing_inside
  where
    inline_rule = mkInlineUnfolding Nothing rhs

---------------------
splitFun :: Id -> IdInfo -> [Demand] -> DmdResult -> Expr Var
         -> UniqSM [(Id, CoreExpr)]
splitFun fn_id fn_info wrap_dmds res_info rhs
  = WARN( not (wrap_dmds `lengthIs` arity), ppr fn_id <+> (ppr arity $$ ppr wrap_dmds $$ ppr res_info) ) 
    (do {
	-- The arity should match the signature
      (work_demands, wrap_fn, work_fn) <- mkWwBodies fun_ty wrap_dmds res_info one_shots
    ; work_uniq <- getUniqueM
    ; let
	work_rhs = work_fn rhs
	work_id  = mkWorkerId work_uniq fn_id (exprType work_rhs) 
		        `setIdOccInfo` occInfo fn_info
				-- Copy over occurrence info from parent
				-- Notably whether it's a loop breaker
				-- Doesn't matter much, since we will simplify next, but
				-- seems right-er to do so

			`setInlineActivation` (inlinePragmaActivation inl_prag)
				-- Any inline activation (which sets when inlining is active) 
				-- on the original function is duplicated on the worker
				-- It *matters* that the pragma stays on the wrapper
				-- It seems sensible to have it on the worker too, although we
				-- can't think of a compelling reason. (In ptic, INLINE things are 
				-- not w/wd). However, the RuleMatchInfo is not transferred since
                                -- it does not make sense for workers to be constructorlike.

			`setIdStrictness` StrictSig (mkTopDmdType work_demands work_res_info)
				-- Even though we may not be at top level, 
				-- it's ok to give it an empty DmdEnv

                        `setIdArity` (exprArity work_rhs)
                                -- Set the arity so that the Core Lint check that the 
                                -- arity is consistent with the demand type goes through

	wrap_rhs  = wrap_fn work_id
	wrap_prag = InlinePragma { inl_inline = Inline
                                 , inl_sat    = Nothing
                                 , inl_act    = ActiveAfter 0
                                 , inl_rule   = rule_match_info }
		-- See Note [Wrapper activation]
		-- The RuleMatchInfo is (and must be) unaffected
		-- The inl_inline is bound to be False, else we would not be
		--    making a wrapper

	wrap_id   = fn_id `setIdUnfolding` mkWwInlineRule work_id wrap_rhs arity
			  `setInlinePragma` wrap_prag
		          `setIdOccInfo` NoOccInfo
			        -- Zap any loop-breaker-ness, to avoid bleating from Lint
				-- about a loop breaker with an INLINE rule

    ; return ([(work_id, work_rhs), (wrap_id, wrap_rhs)]) })
	-- Worker first, because wrapper mentions it
	-- mkWwBodies has already built a wrap_rhs with an INLINE pragma wrapped around it
  where
    fun_ty          = idType fn_id
    inl_prag        = inlinePragInfo fn_info
    rule_match_info = inlinePragmaRuleMatchInfo inl_prag
    arity           = arityInfo fn_info	
    		    -- The arity is set by the simplifier using exprEtaExpandArity
		    -- So it may be more than the number of top-level-visible lambdas

    work_res_info | isBotRes res_info = BotRes	-- Cpr stuff done by wrapper
		  | otherwise	      = TopRes

    one_shots = get_one_shots rhs

-- If the original function has one-shot arguments, it is important to
-- make the wrapper and worker have corresponding one-shot arguments too.
-- Otherwise we spuriously float stuff out of case-expression join points,
-- which is very annoying.
get_one_shots :: Expr Var -> [Bool]
get_one_shots (Lam b e)
  | isId b    = isOneShotLambda b : get_one_shots e
  | otherwise = get_one_shots e
get_one_shots (Note _ e) = get_one_shots e
get_one_shots _    	 = noOneShotInfo

-- See Note [Thunk splitting]
-- splitThunk converts the *non-recursive* binding
--	x = e
-- into
--	x = let x = e
--	    in case x of 
--		 I# y -> let x = I# y in x }
-- See comments above. Is it not beautifully short?
-- Moreover, it works just as well when there are
-- several binders, and if the binders are lifted
-- E.g.     x = e
--     -->  x = let x = e in
--              case x of (a,b) -> let x = (a,b)  in x

splitThunk :: Var -> Expr Var -> UniqSM [(Var, Expr Var)]
splitThunk fn_id rhs = do
    (_, wrap_fn, work_fn) <- mkWWstr [fn_id]
    return [ (fn_id, Let (NonRec fn_id rhs) (wrap_fn (work_fn (Var fn_id)))) ]

worthSplittingFun :: [Demand] -> DmdResult -> Bool
		-- True <=> the wrapper would not be an identity function
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
  -- See Note [Worker-wrapper for bottoming functions]
  where
    worth_it Abs	      = True	-- Absent arg
    worth_it (Eval (Prod _)) = True	-- Product arg to evaluate
    worth_it _    	      = False

worthSplittingThunk :: Maybe Demand	-- Demand on the thunk
		    -> DmdResult	-- CPR info for the thunk
		    -> Bool
worthSplittingThunk maybe_dmd res
  = worth_it maybe_dmd || returnsCPR res
  where
	-- Split if the thing is unpacked
    worth_it (Just (Eval (Prod ds))) = not (all isAbsent ds)
    worth_it _    	   	     = False

mkWrapper :: Type		-- Wrapper type
	  -> StrictSig		-- Wrapper strictness info
	  -> UniqSM (Id -> CoreExpr)	-- Wrapper body, missing worker Id

mkWrapper fun_ty (StrictSig (DmdType _ demands res_info)) = do
    (_, wrap_fn, _) <- mkWwBodies fun_ty demands res_info noOneShotInfo
    return wrap_fn

noOneShotInfo :: [Bool]
noOneShotInfo = repeat False