Vectorise.hs 12 KB
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-- Main entry point to the vectoriser.  It is invoked iff the option '-fvectorise' is passed.
--
-- This module provides the function 'vectorise', which vectorises an entire (desugared) module.
-- It vectorises all type declarations and value bindings.  It also processes all VECTORISE pragmas
-- (aka vectorisation declarations), which can lead to the vectorisation of imported data types
-- and the enrichment of imported functions with vectorised versions.
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module Vectorise ( vectorise )
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where

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import Vectorise.Type.Env
import Vectorise.Type.Type
import Vectorise.Convert
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import Vectorise.Utils.Hoisting
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import Vectorise.Exp
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import Vectorise.Vect
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import Vectorise.Env
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import Vectorise.Monad
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import HscTypes hiding      ( MonadThings(..) )
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import CoreUnfold           ( mkInlineUnfolding )
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import CoreFVs
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import PprCore
import CoreSyn
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import CoreMonad            ( CoreM, getHscEnv )
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import Type
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import Id
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import OccName
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import DynFlags
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import BasicTypes           ( isStrongLoopBreaker )
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import Outputable
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import Util                 ( zipLazy )
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import MonadUtils

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import Control.Monad
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-- | Vectorise a single module.
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--
vectorise :: ModGuts -> CoreM ModGuts
vectorise guts
 = do { hsc_env <- getHscEnv
      ; liftIO $ vectoriseIO hsc_env guts
      }
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-- | Vectorise a single monad, given the dynamic compiler flags and HscEnv.
--
vectoriseIO :: HscEnv -> ModGuts -> IO ModGuts
vectoriseIO hsc_env guts
 = do {   -- Get information about currently loaded external packages.
      ; eps <- hscEPS hsc_env
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          -- Combine vectorisation info from the current module, and external ones.
      ; let info = hptVectInfo hsc_env `plusVectInfo` eps_vect_info eps
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          -- Run the main VM computation.
      ; Just (info', guts') <- initV hsc_env guts info (vectModule guts)
      ; return (guts' { mg_vect_info = info' })
      }
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-- | Vectorise a single module, in the VM monad.
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--
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vectModule :: ModGuts -> VM ModGuts
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vectModule guts@(ModGuts { mg_types      = types
                         , mg_binds      = binds
                         , mg_fam_insts  = fam_insts
                         , mg_vect_decls = vect_decls
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                         })
 = do { dumpOptVt Opt_D_dump_vt_trace "Before vectorisation" $ 
          pprCoreBindings binds
 
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          -- Vectorise the type environment.  This will add vectorised type constructors, their
          -- representaions, and the conrresponding data constructors.  Moreover, we produce
          -- bindings for dfuns and family instances of the classes and type families used in the
          -- DPH library to represent array types.
      ; (types', new_fam_insts, tc_binds) <- vectTypeEnv types [vd | vd@(VectType _ _) <- vect_decls]
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      ; (_, fam_inst_env) <- readGEnv global_fam_inst_env
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          -- Vectorise all the top level bindings.
      ; binds'  <- mapM vectTopBind binds
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      ; return $ guts { mg_types        = types'
                      , mg_binds        = Rec tc_binds : binds'
                      , mg_fam_inst_env = fam_inst_env
                      , mg_fam_insts    = fam_insts ++ new_fam_insts
                      }
      }
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-- |Try to vectorise a top-level binding.  If it doesn't vectorise then return it unharmed.
--
-- For example, for the binding 
--
-- @  
--    foo :: Int -> Int
--    foo = \x -> x + x
-- @
--
-- we get
-- @
--    foo  :: Int -> Int
--    foo  = \x -> vfoo $: x                  
--
--    v_foo :: Closure void vfoo lfoo
--    v_foo = closure vfoo lfoo void        
--
--    vfoo :: Void -> Int -> Int
--    vfoo = ...
--
--    lfoo :: PData Void -> PData Int -> PData Int
--    lfoo = ...
-- @ 
--
-- @vfoo@ is the "vectorised", or scalar, version that does the same as the original
-- function foo, but takes an explicit environment.
--
-- @lfoo@ is the "lifted" version that works on arrays.
--
-- @v_foo@ combines both of these into a `Closure` that also contains the
-- environment.
--
-- The original binding @foo@ is rewritten to call the vectorised version
-- present in the closure.
--
-- Vectorisation may be surpressed by annotating a binding with a 'NOVECTORISE' pragma.  If this
-- pragma is used in a group of mutually recursive bindings, either all or no binding must have
-- the pragma.  If only some bindings are annotated, a fatal error is being raised.
-- FIXME: Once we support partial vectorisation, we may be able to vectorise parts of a group, or
--   we may emit a warning and refrain from vectorising the entire group.
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--
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vectTopBind :: CoreBind -> VM CoreBind
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vectTopBind b@(NonRec var expr)
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  = unlessNoVectDecl $
      do {   -- Vectorise the right-hand side, create an appropriate top-level binding and add it
             -- to the vectorisation map.
         ; (inline, isScalar, expr') <- vectTopRhs [] var expr
         ; var' <- vectTopBinder var inline expr'
         ; when isScalar $ 
             addGlobalScalar var
 
             -- We replace the original top-level binding by a value projected from the vectorised
             -- closure and add any newly created hoisted top-level bindings.
         ; cexpr <- tryConvert var var' expr
         ; hs <- takeHoisted
         ; return . Rec $ (var, cexpr) : (var', expr') : hs
         }
     `orElseV`
       return b
  where
    unlessNoVectDecl vectorise
      = do { hasNoVectDecl <- noVectDecl var
           ; when hasNoVectDecl $
               traceVt "NOVECTORISE" $ ppr var
           ; if hasNoVectDecl then return b else vectorise
           }
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vectTopBind b@(Rec bs)
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  = unlessSomeNoVectDecl $
      do { (vars', _, exprs', hs) <- fixV $ 
             \ ~(_, inlines, rhss, _) ->
               do {   -- Vectorise the right-hand sides, create an appropriate top-level bindings
                      -- and add them to the vectorisation map.
                  ; vars' <- sequence [vectTopBinder var inline rhs
                                      | (var, ~(inline, rhs)) <- zipLazy vars (zip inlines rhss)]
                  ; (inlines, areScalars, exprs') <- mapAndUnzip3M (uncurry $ vectTopRhs vars) bs
                  ; hs <- takeHoisted
                  ; if and areScalars
                    then      -- (1) Entire recursive group is scalar
                              --      => add all variables to the global set of scalars
                         do { mapM_ addGlobalScalar vars
                            ; return (vars', inlines, exprs', hs)
                            }
                    else      -- (2) At least one binding is not scalar
                              --     => vectorise again with empty set of local scalars
                         do { (inlines, _, exprs') <- mapAndUnzip3M (uncurry $ vectTopRhs []) bs
                            ; hs <- takeHoisted
                            ; return (vars', inlines, exprs', hs)
                            }
                  }
                       
             -- Replace the original top-level bindings by a values projected from the vectorised
             -- closures and add any newly created hoisted top-level bindings to the group.
         ; cexprs <- sequence $ zipWith3 tryConvert vars vars' exprs
         ; return . Rec $ zip vars cexprs ++ zip vars' exprs' ++ hs
         }
     `orElseV`
       return b    
  where
    (vars, exprs) = unzip bs

    unlessSomeNoVectDecl vectorise
      = do { hasNoVectDecls <- mapM noVectDecl vars
           ; when (and hasNoVectDecls) $
               traceVt "NOVECTORISE" $ ppr vars
           ; if and hasNoVectDecls 
             then return b                              -- all bindings have 'NOVECTORISE'
             else if or hasNoVectDecls 
             then cantVectorise noVectoriseErr (ppr b)  -- some (but not all) have 'NOVECTORISE'
             else vectorise                             -- no binding has a 'NOVECTORISE' decl
           }
    noVectoriseErr = "NOVECTORISE must be used on all or no bindings of a recursive group"
     
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-- | Make the vectorised version of this top level binder, and add the mapping
--   between it and the original to the state. For some binder @foo@ the vectorised
--   version is @$v_foo@
--
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--   NOTE: 'vectTopBinder' *MUST* be lazy in inline and expr because of how it is
--   used inside of 'fixV' in 'vectTopBind'.
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--
vectTopBinder :: Var      -- ^ Name of the binding.
              -> Inline   -- ^ Whether it should be inlined, used to annotate it.
              -> CoreExpr -- ^ RHS of binding, used to set the 'Unfolding' of the returned 'Var'.
              -> VM Var   -- ^ Name of the vectorised binding.
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vectTopBinder var inline expr
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 = do {   -- Vectorise the type attached to the var.
      ; vty  <- vectType (idType var)
      
          -- If there is a vectorisation declartion for this binding, make sure that its type
          --  matches
      ; vectDecl <- lookupVectDecl var
      ; case vectDecl of
          Nothing                 -> return ()
          Just (vdty, _) 
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            | eqType vty vdty -> return ()
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            | otherwise           -> 
              cantVectorise ("Type mismatch in vectorisation pragma for " ++ show var) $
                (text "Expected type" <+> ppr vty)
                $$
                (text "Inferred type" <+> ppr vdty)

          -- Make the vectorised version of binding's name, and set the unfolding used for inlining
      ; var' <- liftM (`setIdUnfoldingLazily` unfolding) 
                $  cloneId mkVectOcc var vty

          -- Add the mapping between the plain and vectorised name to the state.
      ; defGlobalVar var var'

      ; return var'
    }
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  where
    unfolding = case inline of
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                  Inline arity -> mkInlineUnfolding (Just arity) expr
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                  DontInline   -> noUnfolding
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-- | Vectorise the RHS of a top-level binding, in an empty local environment.
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--
-- We need to distinguish three cases:
--
-- (1) We have a (non-scalar) vectorisation declaration for the variable (which explicitly provides
--     vectorised code implemented by the user)
--     => no automatic vectorisation & instead use the user-supplied code
-- 
-- (2) We have a scalar vectorisation declaration for the variable
--     => generate vectorised code that uses a scalar 'map'/'zipWith' to lift the computation
-- 
-- (3) There is no vectorisation declaration for the variable
--     => perform automatic vectorisation of the RHS
--
vectTopRhs :: [Var]           -- ^ Names of all functions in the rec block
           -> Var             -- ^ Name of the binding.
           -> CoreExpr        -- ^ Body of the binding.
           -> VM ( Inline     -- (1) inline specification for the binding
                 , Bool       -- (2) whether the right-hand side is a scalar computation
                 , CoreExpr)  -- (3) the vectorised right-hand side
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vectTopRhs recFs var expr
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  = closedV
  $ do { traceVt ("vectTopRhs of " ++ show var) $ ppr expr
  
       ; globalScalar <- isGlobalScalar var
       ; vectDecl     <- lookupVectDecl var
       ; rhs globalScalar vectDecl
       }
  where
    rhs _globalScalar (Just (_, expr'))               -- Case (1)
      = return (inlineMe, False, expr')
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    rhs True          Nothing                         -- Case (2)
      = do { expr' <- vectScalarFun True recFs expr
           ; return (inlineMe, True, vectorised expr')
           }
    rhs False         Nothing                         -- Case (3)
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      = do { let fvs = freeVars expr
           ; (inline, isScalar, vexpr) <- inBind var $
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                                          vectPolyExpr (isStrongLoopBreaker $ idOccInfo var) recFs fvs
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           ; return (inline, isScalar, vectorised vexpr)
           }
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-- | Project out the vectorised version of a binding from some closure,
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--   or return the original body if that doesn't work or the binding is scalar. 
--
tryConvert :: Var       -- ^ Name of the original binding (eg @foo@)
           -> Var       -- ^ Name of vectorised version of binding (eg @$vfoo@)
           -> CoreExpr  -- ^ The original body of the binding.
           -> VM CoreExpr
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tryConvert var vect_var rhs
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  = do { globalScalar <- isGlobalScalar var
       ; if globalScalar
         then
           return rhs
         else
           fromVect (idType var) (Var vect_var) `orElseV` return rhs
       }