futhark-0.10.1: src/Futhark/CodeGen/ImpGen/Kernels/Base.hs
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE LambdaCase #-}
{-# LANGUAGE TypeFamilies #-}
module Futhark.CodeGen.ImpGen.Kernels.Base
( KernelConstants (..)
, inKernelOperations
, computeKernelUses
, keyWithEntryPoint
, CallKernelGen
, InKernelGen
, computeThreadChunkSize
, kernelInitialisation
, kernelInitialisationSetSpace
, setSpaceIndices
, makeAllMemoryGlobal
, allThreads
, compileKernelStms
, groupReduce
, groupScan
, isActive
, sKernel
, sReplicate
, sIota
, sCopy
, atomicUpdate
, atomicUpdateLocking
, Locking(..)
, AtomicUpdate
)
where
import Control.Arrow ((&&&))
import Control.Monad.Except
import Control.Monad.Reader
import Data.Maybe
import qualified Data.Map.Strict as M
import qualified Data.Set as S
import Data.List
import Prelude hiding (quot, rem)
import Futhark.Error
import Futhark.MonadFreshNames
import Futhark.Transform.Rename
import Futhark.Representation.ExplicitMemory
import qualified Futhark.CodeGen.ImpCode.Kernels as Imp
import Futhark.CodeGen.ImpCode.Kernels (bytes)
import qualified Futhark.CodeGen.ImpGen as ImpGen
import Futhark.CodeGen.ImpGen ((<--),
sFor, sWhile, sComment, sIf, sWhen, sUnless,
sOp,
dPrim, dPrim_, dPrimV)
import Futhark.Tools (partitionChunkedKernelLambdaParameters)
import Futhark.Util.IntegralExp (quotRoundingUp, quot, rem, IntegralExp)
import Futhark.Util (splitAt3, maybeNth, takeLast)
type CallKernelGen = ImpGen.ImpM ExplicitMemory Imp.HostOp
type InKernelGen = ImpGen.ImpM InKernel Imp.KernelOp
data KernelConstants = KernelConstants
{ kernelGlobalThreadId :: Imp.Exp
, kernelLocalThreadId :: Imp.Exp
, kernelGroupId :: Imp.Exp
, kernelGlobalThreadIdVar :: VName
, kernelLocalThreadIdVar :: VName
, kernelGroupIdVar :: VName
, kernelGroupSize :: Imp.Exp
, kernelNumGroups :: Imp.Exp
, kernelNumThreads :: Imp.Exp
, kernelWaveSize :: Imp.Exp
, kernelDimensions :: [(VName, Imp.Exp)]
, kernelThreadActive :: Imp.Exp
, kernelStreamed :: [(VName, Imp.DimSize)]
-- ^ Chunk sizes and their maximum size. Hint
-- for unrolling.
}
inKernelOperations :: KernelConstants -> ImpGen.Operations InKernel Imp.KernelOp
inKernelOperations constants = (ImpGen.defaultOperations $ compileInKernelOp constants)
{ ImpGen.opsCopyCompiler = inKernelCopy
, ImpGen.opsExpCompiler = inKernelExpCompiler
, ImpGen.opsStmsCompiler = \_ -> compileKernelStms constants
}
keyWithEntryPoint :: Name -> Name -> Name
keyWithEntryPoint fname key =
nameFromString $ nameToString fname ++ "." ++ nameToString key
-- | We have no bulk copy operation (e.g. memmove) inside kernels, so
-- turn any copy into a loop.
inKernelCopy :: ImpGen.CopyCompiler InKernel Imp.KernelOp
inKernelCopy = ImpGen.copyElementWise
compileInKernelOp :: KernelConstants -> Pattern InKernel -> Op InKernel
-> InKernelGen ()
compileInKernelOp _ (Pattern _ [mem]) Alloc{} =
compilerLimitationS $ "Cannot allocate memory block " ++ pretty mem ++ " in kernel."
compileInKernelOp _ dest Alloc{} =
compilerBugS $ "Invalid target for in-kernel allocation: " ++ show dest
compileInKernelOp constants pat (Inner op) =
compileKernelExp constants pat op
inKernelExpCompiler :: ImpGen.ExpCompiler InKernel Imp.KernelOp
inKernelExpCompiler _ (BasicOp (Assert _ _ (loc, locs))) =
compilerLimitationS $
unlines [ "Cannot compile assertion at " ++
intercalate " -> " (reverse $ map locStr $ loc:locs) ++
" inside parallel kernel."
, "As a workaround, surround the expression with 'unsafe'."]
-- The static arrays stuff does not work inside kernels.
inKernelExpCompiler (Pattern _ [dest]) (BasicOp (ArrayLit es _)) =
forM_ (zip [0..] es) $ \(i,e) ->
ImpGen.copyDWIM (patElemName dest) [fromIntegral (i::Int32)] e []
inKernelExpCompiler dest e =
ImpGen.defCompileExp dest e
compileKernelExp :: KernelConstants -> Pattern InKernel -> KernelExp InKernel
-> InKernelGen ()
compileKernelExp _ pat (Barrier ses) = do
forM_ (zip (patternNames pat) ses) $ \(d, se) ->
ImpGen.copyDWIM d [] se []
sOp Imp.LocalBarrier
compileKernelExp _ (Pattern [] [size]) (SplitSpace o w i elems_per_thread) = do
num_elements <- Imp.elements <$> ImpGen.compileSubExp w
i' <- ImpGen.compileSubExp i
elems_per_thread' <- Imp.elements <$> ImpGen.compileSubExp elems_per_thread
computeThreadChunkSize o i' elems_per_thread' num_elements (patElemName size)
compileKernelExp constants pat (Combine (CombineSpace scatter cspace) _ aspace body) = do
-- First we compute how many times we have to iterate to cover
-- cspace with our group size. It is a fairly common case that
-- we statically know that this requires 1 iteration, so we
-- could detect it and not generate a loop in that case.
-- However, it seems to have no impact on performance (an extra
-- conditional jump), so for simplicity we just always generate
-- the loop.
let cspace_dims = map (streamBounded . snd) cspace
num_iters
| cspace_dims == [kernelGroupSize constants] = 1
| otherwise = product cspace_dims `quotRoundingUp`
kernelGroupSize constants
iter <- newVName "comb_iter"
sFor iter Int32 num_iters $ do
mapM_ ((`dPrim_` int32) . fst) cspace
-- Compute the *flat* array index.
cid <- dPrimV "flat_comb_id" $
Imp.var iter int32 * kernelGroupSize constants +
kernelLocalThreadId constants
-- Turn it into a nested array index.
zipWithM_ (<--) (map fst cspace) $ unflattenIndex cspace_dims (Imp.var cid int32)
-- Construct the body. This is mostly about the book-keeping
-- for the scatter-like part.
let (scatter_ws, scatter_ns, _scatter_vs) = unzip3 scatter
scatter_ws_repl = concat $ zipWith replicate scatter_ns scatter_ws
(scatter_pes, normal_pes) =
splitAt (sum scatter_ns) $ patternElements pat
(res_is, res_vs, res_normal) =
splitAt3 (sum scatter_ns) (sum scatter_ns) $ bodyResult body
-- Execute the body if we are within bounds.
sWhen (isActive cspace .&&. isActive aspace) $ allThreads constants $
ImpGen.compileStms (freeIn $ bodyResult body) (stmsToList $ bodyStms body) $ do
forM_ (zip4 scatter_ws_repl res_is res_vs scatter_pes) $
\(w, res_i, res_v, scatter_pe) -> do
let res_i' = ImpGen.compileSubExpOfType int32 res_i
w' = ImpGen.compileSubExpOfType int32 w
-- We have to check that 'res_i' is in-bounds wrt. an array of size 'w'.
in_bounds = 0 .<=. res_i' .&&. res_i' .<. w'
sWhen in_bounds $ ImpGen.copyDWIM (patElemName scatter_pe) [res_i'] res_v []
forM_ (zip normal_pes res_normal) $ \(pe, res) ->
ImpGen.copyDWIM (patElemName pe) local_index res []
sOp Imp.LocalBarrier
where streamBounded (Var v)
| Just x <- lookup v $ kernelStreamed constants =
Imp.sizeToExp x
streamBounded se = ImpGen.compileSubExpOfType int32 se
local_index = map (ImpGen.compileSubExpOfType int32 . Var . fst) cspace
compileKernelExp constants (Pattern _ dests) (GroupReduce w lam input) = do
let [my_index_param, offset_param] = take 2 $ lambdaParams lam
lam' = lam { lambdaParams = drop 2 $ lambdaParams lam }
dPrim_ (paramName my_index_param) int32
dPrim_ (paramName offset_param) int32
paramName my_index_param <-- kernelGlobalThreadId constants
w' <- ImpGen.compileSubExp w
groupReduceWithOffset constants (paramName offset_param) w' lam' $ map snd input
sOp Imp.LocalBarrier
-- The final result will be stored in element 0 of the local memory array.
forM_ (zip dests input) $ \(dest, (_, arr)) ->
ImpGen.copyDWIM (patElemName dest) [] (Var arr) [0]
compileKernelExp constants _ (GroupScan w lam input) = do
w' <- ImpGen.compileSubExp w
groupScan constants Nothing w' lam $ map snd input
compileKernelExp constants (Pattern _ final) (GroupStream w maxchunk lam accs _arrs) = do
let GroupStreamLambda block_size block_offset acc_params arr_params body = lam
block_offset' = Imp.var block_offset int32
w' <- ImpGen.compileSubExp w
max_block_size <- ImpGen.compileSubExp maxchunk
ImpGen.dLParams (acc_params++arr_params)
zipWithM_ ImpGen.compileSubExpTo (map paramName acc_params) accs
dPrim_ block_size int32
-- If the GroupStream is morally just a do-loop, generate simpler code.
case mapM isSimpleThreadInSpace $ stmsToList $ bodyStms body of
Just stms' | ValueExp x <- max_block_size, oneIsh x -> do
let body' = body { bodyStms = stmsFromList stms' }
body'' = allThreads constants $
ImpGen.compileLoopBody (map paramName acc_params) body'
block_size <-- 1
-- Check if loop is candidate for unrolling.
let loop =
case w of
Var w_var | Just w_bound <- lookup w_var $ kernelStreamed constants,
w_bound /= Imp.ConstSize 1 ->
-- Candidate for unrolling, so generate two loops.
sIf (w' .==. Imp.sizeToExp w_bound)
(sFor block_offset Int32 (Imp.sizeToExp w_bound) body'')
(sFor block_offset Int32 w' body'')
_ -> sFor block_offset Int32 w' body''
if kernelThreadActive constants == Imp.ValueExp (BoolValue True)
then loop
else sWhen (kernelThreadActive constants) loop
_ -> do
dPrim_ block_offset int32
let body' = streaming constants block_size maxchunk $
ImpGen.compileBody' acc_params body
block_offset <-- 0
let not_at_end = block_offset' .<. w'
set_block_size =
sIf (w' - block_offset' .<. max_block_size)
(block_size <-- (w' - block_offset'))
(block_size <-- max_block_size)
increase_offset =
block_offset <-- block_offset' + max_block_size
-- Three cases to consider for simpler generated code based
-- on max block size: (0) if full input size, do not
-- generate a loop; (1) if one, generate for-loop (2)
-- otherwise, generate chunked while-loop.
if max_block_size == w' then
(block_size <-- w') >> body'
else if max_block_size == Imp.ValueExp (value (1::Int32)) then do
block_size <-- w'
sFor block_offset Int32 w' body'
else
sWhile not_at_end $
set_block_size >> body' >> increase_offset
forM_ (zip final acc_params) $ \(pe, p) ->
ImpGen.copyDWIM (patElemName pe) [] (Var $ paramName p) []
where isSimpleThreadInSpace (Let _ _ Op{}) = Nothing
isSimpleThreadInSpace bnd = Just bnd
compileKernelExp _ _ (GroupGenReduce w arrs op bucket values locks) = do
-- Check if bucket is in-bounds
bucket' <- mapM ImpGen.compileSubExp bucket
w' <- mapM ImpGen.compileSubExp w
num_locks <- ImpGen.compileSubExpOfType int32 . arraySize 0 <$> lookupType locks
let locking = Locking locks 0 1 0 $ (`rem` num_locks) . sum
values_params = takeLast (length values) $ lambdaParams op
sWhen (indexInBounds bucket' w') $ do
forM_ (zip values_params values) $ \(p, v) ->
ImpGen.copyDWIM (paramName p) [] v []
atomicUpdate arrs bucket' op locking
where indexInBounds inds bounds =
foldl1 (.&&.) $ zipWith checkBound inds bounds
where checkBound ind bound = 0 .<=. ind .&&. ind .<. bound
compileKernelExp _ dest e =
compilerBugS $ unlines ["Invalid target", " " ++ show dest,
"for kernel expression", " " ++ pretty e]
streaming :: KernelConstants -> VName -> SubExp -> InKernelGen () -> InKernelGen ()
streaming constants chunksize bound m = do
bound' <- ImpGen.subExpToDimSize bound
let constants' =
constants { kernelStreamed = (chunksize, bound') : kernelStreamed constants }
ImpGen.emit =<< ImpGen.subImpM_ (inKernelOperations constants') m
-- | Locking strategy used for an atomic update.
data Locking =
Locking { lockingArray :: VName
-- ^ Array containing the lock.
, lockingIsUnlocked :: Imp.Exp
-- ^ Value for us to consider the lock free.
, lockingToLock :: Imp.Exp
-- ^ What to write when we lock it.
, lockingToUnlock :: Imp.Exp
-- ^ What to write when we unlock it.
, lockingMapping :: [Imp.Exp] -> Imp.Exp
-- ^ A transformation from the logical lock index to the
-- physical position in the array. This can also be used
-- to make the lock array smaller.
}
-- | A function for generating code for an atomic update. Assumes
-- that the bucket is in-bounds.
type AtomicUpdate lore =
[VName] -> [Imp.Exp] -> ImpGen.ImpM lore Imp.KernelOp ()
atomicUpdate :: ExplicitMemorish lore =>
[VName] -> [Imp.Exp] -> Lambda lore -> Locking
-> ImpGen.ImpM lore Imp.KernelOp ()
atomicUpdate arrs bucket lam locking =
case atomicUpdateLocking lam of
Left f -> f arrs bucket
Right f -> f locking arrs bucket
-- | 'atomicUpdate', but where it is explicitly visible whether a
-- locking strategy is necessary.
atomicUpdateLocking :: ExplicitMemorish lore =>
Lambda lore
-> Either (AtomicUpdate lore) (Locking -> AtomicUpdate lore)
atomicUpdateLocking lam
| Just ops_and_ts <- splitOp lam,
all (\(_, t, _) -> primBitSize t == 32) ops_and_ts = Left $ \arrs bucket ->
-- If the operator is a vectorised binary operator on 32-bit values,
-- we can use a particularly efficient implementation. If the
-- operator has an atomic implementation we use that, otherwise it
-- is still a binary operator which can be implemented by atomic
-- compare-and-swap if 32 bits.
forM_ (zip arrs ops_and_ts) $ \(a, (op, t, val)) -> do
-- Common variables.
old <- dPrim "old" t
(arr', _a_space, bucket_offset) <- ImpGen.fullyIndexArray a bucket
case opHasAtomicSupport old arr' bucket_offset op of
Just f -> sOp $ f val
Nothing -> do
-- Code generation target:
--
-- old = d_his[idx];
-- do {
-- assumed = old;
-- tmp = OP::apply(val, assumed);
-- old = atomicCAS(&d_his[idx], assumed, tmp);
-- } while(assumed != old);
assumed <- dPrim "assumed" t
run_loop <- dPrimV "run_loop" 1
ImpGen.copyDWIM old [] (Var a) bucket
-- Critical section
x <- dPrim "x" t
y <- dPrim "y" t
-- While-loop: Try to insert your value
let (toBits, fromBits) =
case t of FloatType Float32 -> (\v -> Imp.FunExp "to_bits32" [v] int32,
\v -> Imp.FunExp "from_bits32" [v] t)
_ -> (id, id)
sWhile (Imp.var run_loop int32) $ do
assumed <-- Imp.var old t
x <-- val
y <-- Imp.var assumed t
x <-- Imp.BinOpExp op (Imp.var x t) (Imp.var y t)
old_bits <- dPrim "old_bits" int32
sOp $ Imp.Atomic $
Imp.AtomicCmpXchg old_bits arr' bucket_offset
(toBits (Imp.var assumed t)) (toBits (Imp.var x t))
old <-- fromBits (Imp.var old_bits int32)
sWhen (toBits (Imp.var assumed t) .==. Imp.var old_bits int32)
(run_loop <-- 0)
where opHasAtomicSupport old arr' bucket' bop = do
let atomic f = Imp.Atomic . f old arr' bucket'
atomic <$> Imp.atomicBinOp bop
atomicUpdateLocking op = Right $ \locking arrs bucket -> do
old <- dPrim "old" int32
continue <- dPrimV "continue" true
-- Correctly index into locks.
(locks', _locks_space, locks_offset) <-
ImpGen.fullyIndexArray (lockingArray locking) [lockingMapping locking bucket]
-- Critical section
let try_acquire_lock =
sOp $ Imp.Atomic $
Imp.AtomicCmpXchg old locks' locks_offset (lockingIsUnlocked locking) (lockingToLock locking)
lock_acquired = Imp.var old int32 .==. lockingIsUnlocked locking
-- Even the releasing is done with an atomic rather than a
-- simple write, for memory coherency reasons.
release_lock =
sOp $ Imp.Atomic $
Imp.AtomicCmpXchg old locks' locks_offset (lockingToLock locking) (lockingToUnlock locking)
break_loop = continue <-- false
-- Preparing parameters. It is assumed that the caller has already
-- filled the arr_params. We copy the current value to the
-- accumulator parameters.
--
-- Note the use of 'everythingVolatile' when reading and writing the
-- buckets. This was necessary to ensure correct execution on a
-- newer NVIDIA GPU (RTX 2080). The 'volatile' modifiers likely
-- make the writes pass through the (SM-local) L1 cache, which is
-- necessary here, because we are really doing device-wide
-- synchronisation without atomics (naughty!).
let (acc_params, _arr_params) = splitAt (length arrs) $ lambdaParams op
bind_acc_params =
ImpGen.everythingVolatile $
ImpGen.sComment "bind lhs" $
forM_ (zip acc_params arrs) $ \(acc_p, arr) ->
ImpGen.copyDWIM (paramName acc_p) [] (Var arr) bucket
let op_body = ImpGen.sComment "execute operation" $
ImpGen.compileBody' acc_params $ lambdaBody op
do_gen_reduce =
ImpGen.everythingVolatile $
ImpGen.sComment "update global result" $
zipWithM_ (writeArray bucket) arrs $ map (Var . paramName) acc_params
-- While-loop: Try to insert your value
sWhile (Imp.var continue Bool) $ do
try_acquire_lock
sWhen lock_acquired $ do
ImpGen.dLParams acc_params
bind_acc_params
op_body
do_gen_reduce
sOp Imp.MemFence
release_lock
break_loop
sOp Imp.MemFence
where writeArray bucket arr val = ImpGen.copyDWIM arr bucket val []
-- | Horizontally fission a lambda that models a binary operator.
splitOp :: Attributes lore => Lambda lore -> Maybe [(BinOp, PrimType, Imp.Exp)]
splitOp lam = mapM splitStm $ bodyResult $ lambdaBody lam
where n = length $ lambdaReturnType lam
splitStm (Var res) = do
Let (Pattern [] [pe]) _ (BasicOp (BinOp op (Var x) (Var y))) <-
find (([res]==) . patternNames . stmPattern) $
stmsToList $ bodyStms $ lambdaBody lam
i <- Var res `elemIndex` bodyResult (lambdaBody lam)
xp <- maybeNth i $ lambdaParams lam
yp <- maybeNth (n+i) $ lambdaParams lam
guard $ paramName xp == x
guard $ paramName yp == y
Prim t <- Just $ patElemType pe
return (op, t, Imp.var (paramName yp) t)
splitStm _ = Nothing
computeKernelUses :: FreeIn a =>
a -> [VName]
-> CallKernelGen ([Imp.KernelUse], [Imp.LocalMemoryUse])
computeKernelUses kernel_body bound_in_kernel = do
let actually_free = freeIn kernel_body `S.difference` S.fromList bound_in_kernel
-- Compute the variables that we need to pass to the kernel.
reads_from <- readsFromSet actually_free
-- Are we using any local memory?
local_memory <- computeLocalMemoryUse actually_free
return (nub reads_from, nub local_memory)
readsFromSet :: Names -> CallKernelGen [Imp.KernelUse]
readsFromSet free =
fmap catMaybes $
forM (S.toList free) $ \var -> do
t <- lookupType var
case t of
Array {} -> return Nothing
Mem _ (Space "local") -> return Nothing
Mem {} -> return $ Just $ Imp.MemoryUse var
Prim bt ->
isConstExp var >>= \case
Just ce -> return $ Just $ Imp.ConstUse var ce
Nothing | bt == Cert -> return Nothing
| otherwise -> return $ Just $ Imp.ScalarUse var bt
computeLocalMemoryUse :: Names -> CallKernelGen [Imp.LocalMemoryUse]
computeLocalMemoryUse free =
fmap catMaybes $
forM (S.toList free) $ \var -> do
t <- lookupType var
case t of
Mem memsize (Space "local") -> do
memsize' <- localMemSize =<< ImpGen.subExpToDimSize memsize
return $ Just (var, memsize')
_ -> return Nothing
localMemSize :: Imp.MemSize -> CallKernelGen (Either Imp.MemSize Imp.KernelConstExp)
localMemSize (Imp.ConstSize x) =
return $ Right $ ValueExp $ IntValue $ Int64Value x
localMemSize (Imp.VarSize v) = isConstExp v >>= \case
Just e | isStaticExp e -> return $ Right e
_ -> return $ Left $ Imp.VarSize v
isConstExp :: VName -> CallKernelGen (Maybe Imp.KernelConstExp)
isConstExp v = do
vtable <- ImpGen.getVTable
fname <- asks ImpGen.envFunction
let lookupConstExp name = constExp =<< hasExp =<< M.lookup name vtable
constExp (Op (Inner (GetSize key _))) =
Just $ LeafExp (Imp.SizeConst $ keyWithEntryPoint fname key) int32
constExp e = primExpFromExp lookupConstExp e
return $ lookupConstExp v
where hasExp (ImpGen.ArrayVar e _) = e
hasExp (ImpGen.ScalarVar e _) = e
hasExp (ImpGen.MemVar e _) = e
-- | Only some constant expressions qualify as *static* expressions,
-- which we can use for static memory allocation. This is a bit of a
-- hack, as it is primarly motivated by what you can put as the size
-- when declaring an array in C.
isStaticExp :: Imp.KernelConstExp -> Bool
isStaticExp LeafExp{} = True
isStaticExp ValueExp{} = True
isStaticExp (BinOpExp Add{} x y) = isStaticExp x && isStaticExp y
isStaticExp (BinOpExp Sub{} x y) = isStaticExp x && isStaticExp y
isStaticExp (BinOpExp Mul{} x y) = isStaticExp x && isStaticExp y
isStaticExp _ = False
computeThreadChunkSize :: SplitOrdering
-> Imp.Exp
-> Imp.Count Imp.Elements
-> Imp.Count Imp.Elements
-> VName
-> ImpGen.ImpM lore op ()
computeThreadChunkSize (SplitStrided stride) thread_index elements_per_thread num_elements chunk_var = do
stride' <- ImpGen.compileSubExp stride
chunk_var <--
Imp.BinOpExp (SMin Int32)
(Imp.innerExp elements_per_thread)
((Imp.innerExp num_elements - thread_index) `quotRoundingUp` stride')
computeThreadChunkSize SplitContiguous thread_index elements_per_thread num_elements chunk_var = do
starting_point <- dPrimV "starting_point" $
thread_index * Imp.innerExp elements_per_thread
remaining_elements <- dPrimV "remaining_elements" $
Imp.innerExp num_elements - Imp.var starting_point int32
let no_remaining_elements = Imp.var remaining_elements int32 .<=. 0
beyond_bounds = Imp.innerExp num_elements .<=. Imp.var starting_point int32
sIf (no_remaining_elements .||. beyond_bounds)
(chunk_var <-- 0)
(sIf is_last_thread
(chunk_var <-- Imp.innerExp last_thread_elements)
(chunk_var <-- Imp.innerExp elements_per_thread))
where last_thread_elements =
num_elements - Imp.elements thread_index * elements_per_thread
is_last_thread =
Imp.innerExp num_elements .<.
(thread_index + 1) * Imp.innerExp elements_per_thread
kernelInitialisationSetSpace :: KernelSpace -> InKernelGen ()
-> ImpGen.ImpM lore op (KernelConstants, ImpGen.ImpM InKernel Imp.KernelOp ())
kernelInitialisationSetSpace space set_space = do
group_size' <- ImpGen.compileSubExp $ spaceGroupSize space
num_threads' <- ImpGen.compileSubExp $ spaceNumThreads space
num_groups <- ImpGen.compileSubExp $ spaceNumGroups space
let global_tid = spaceGlobalId space
local_tid = spaceLocalId space
group_id = spaceGroupId space
wave_size <- newVName "wave_size"
inner_group_size <- newVName "group_size"
let (space_is, space_dims) = unzip $ spaceDimensions space
space_dims' <- mapM ImpGen.compileSubExp space_dims
let constants =
KernelConstants
(Imp.var global_tid int32)
(Imp.var local_tid int32)
(Imp.var group_id int32)
global_tid local_tid group_id
group_size' num_groups num_threads'
(Imp.var wave_size int32) (zip space_is space_dims')
(if null (spaceDimensions space)
then true else isActive (spaceDimensions space)) mempty
let set_constants = do
dPrim_ wave_size int32
dPrim_ inner_group_size int32
ImpGen.dScope Nothing (scopeOfKernelSpace space)
sOp (Imp.GetGlobalId global_tid 0)
sOp (Imp.GetLocalId local_tid 0)
sOp (Imp.GetLocalSize inner_group_size 0)
sOp (Imp.GetLockstepWidth wave_size)
sOp (Imp.GetGroupId group_id 0)
set_space
return (constants, set_constants)
kernelInitialisation :: KernelSpace
-> ImpGen.ImpM lore op (KernelConstants, ImpGen.ImpM InKernel Imp.KernelOp ())
kernelInitialisation space =
kernelInitialisationSetSpace space $
setSpaceIndices (Imp.var (spaceGlobalId space) int32) space
setSpaceIndices :: Imp.Exp -> KernelSpace -> InKernelGen ()
setSpaceIndices gtid space =
case spaceStructure space of
FlatThreadSpace is_and_dims ->
flatSpaceWith gtid is_and_dims
NestedThreadSpace is_and_dims -> do
let (gtids, gdims, ltids, ldims) = unzip4 is_and_dims
gdims' <- mapM ImpGen.compileSubExp gdims
ldims' <- mapM ImpGen.compileSubExp ldims
let (gtid_es, ltid_es) = unzip $ unflattenNestedIndex gdims' ldims' gtid
zipWithM_ (<--) gtids gtid_es
zipWithM_ (<--) ltids ltid_es
where flatSpaceWith base is_and_dims = do
let (is, dims) = unzip is_and_dims
dims' <- mapM ImpGen.compileSubExp dims
let index_expressions = unflattenIndex dims' base
zipWithM_ (<--) is index_expressions
isActive :: [(VName, SubExp)] -> Imp.Exp
isActive limit = case actives of
[] -> Imp.ValueExp $ BoolValue True
x:xs -> foldl (.&&.) x xs
where (is, ws) = unzip limit
actives = zipWith active is $ map (ImpGen.compileSubExpOfType Bool) ws
active i = (Imp.var i int32 .<.)
unflattenNestedIndex :: IntegralExp num => [num] -> [num] -> num -> [(num,num)]
unflattenNestedIndex global_dims group_dims global_id =
zip global_is local_is
where num_groups_dims = zipWith quotRoundingUp global_dims group_dims
group_size = product group_dims
group_id = global_id `Futhark.Util.IntegralExp.quot` group_size
local_id = global_id `Futhark.Util.IntegralExp.rem` group_size
group_is = unflattenIndex num_groups_dims group_id
local_is = unflattenIndex group_dims local_id
global_is = zipWith (+) local_is $ zipWith (*) group_is group_dims
-- | Change every memory block to be in the global address space,
-- except those who are in the local memory space. This only affects
-- generated code - we still need to make sure that the memory is
-- actually present on the device (and dared as variables in the
-- kernel).
makeAllMemoryGlobal :: CallKernelGen a -> CallKernelGen a
makeAllMemoryGlobal =
local (\env -> env { ImpGen.envDefaultSpace = Imp.Space "global" }) .
ImpGen.localVTable (M.map globalMemory)
where globalMemory (ImpGen.MemVar _ entry)
| ImpGen.entryMemSpace entry /= Space "local" =
ImpGen.MemVar Nothing entry { ImpGen.entryMemSpace = Imp.Space "global" }
globalMemory entry =
entry
allThreads :: KernelConstants -> InKernelGen () -> InKernelGen ()
allThreads constants = ImpGen.emit <=< ImpGen.subImpM_ (inKernelOperations constants')
where constants' =
constants { kernelThreadActive = Imp.ValueExp (BoolValue True) }
writeParamToLocalMemory :: Typed (MemBound u) =>
Imp.Exp -> (VName, t) -> Param (MemBound u)
-> ImpGen.ImpM lore op ()
writeParamToLocalMemory i (mem, _) param
| Prim t <- paramType param =
ImpGen.emit $
Imp.Write mem (bytes i') bt (Space "local") Imp.Volatile $
Imp.var (paramName param) t
| otherwise =
return ()
where i' = i * Imp.LeafExp (Imp.SizeOf bt) int32
bt = elemType $ paramType param
readParamFromLocalMemory :: Typed (MemBound u) =>
VName -> Imp.Exp -> Param (MemBound u) -> (VName, t)
-> ImpGen.ImpM lore op ()
readParamFromLocalMemory index i param (l_mem, _)
| Prim _ <- paramType param =
paramName param <--
Imp.index l_mem (bytes i') bt (Space "local") Imp.Volatile
| otherwise = index <-- i
where i' = i * Imp.LeafExp (Imp.SizeOf bt) int32
bt = elemType $ paramType param
groupReduce :: ExplicitMemorish lore =>
KernelConstants
-> Imp.Exp
-> Lambda lore
-> [VName]
-> ImpGen.ImpM lore Imp.KernelOp ()
groupReduce constants w lam arrs = do
offset <- dPrim "offset" int32
groupReduceWithOffset constants offset w lam arrs
groupReduceWithOffset :: ExplicitMemorish lore =>
KernelConstants
-> VName
-> Imp.Exp
-> Lambda lore
-> [VName]
-> ImpGen.ImpM lore Imp.KernelOp ()
groupReduceWithOffset constants offset w lam arrs = do
let (reduce_acc_params, reduce_arr_params) = splitAt (length arrs) $ lambdaParams lam
skip_waves <- dPrim "skip_waves" int32
ImpGen.dLParams $ lambdaParams lam
offset <-- 0
ImpGen.comment "participating threads read initial accumulator" $
sWhen (local_tid .<. w) $
zipWithM_ readReduceArgument reduce_acc_params arrs
let do_reduce = do ImpGen.comment "read array element" $
zipWithM_ readReduceArgument reduce_arr_params arrs
ImpGen.comment "apply reduction operation" $
ImpGen.compileBody' reduce_acc_params $ lambdaBody lam
ImpGen.comment "write result of operation" $
zipWithM_ writeReduceOpResult reduce_acc_params arrs
in_wave_reduce = ImpGen.everythingVolatile do_reduce
wave_size = kernelWaveSize constants
group_size = kernelGroupSize constants
wave_id = local_tid `quot` wave_size
in_wave_id = local_tid - wave_id * wave_size
num_waves = (group_size + wave_size - 1) `quot` wave_size
arg_in_bounds = local_tid + Imp.var offset int32 .<. w
doing_in_wave_reductions =
Imp.var offset int32 .<. wave_size
apply_in_in_wave_iteration =
(in_wave_id .&. (2 * Imp.var offset int32 - 1)) .==. 0
in_wave_reductions = do
offset <-- 1
sWhile doing_in_wave_reductions $ do
sWhen (arg_in_bounds .&&. apply_in_in_wave_iteration)
in_wave_reduce
offset <-- Imp.var offset int32 * 2
doing_cross_wave_reductions =
Imp.var skip_waves int32 .<. num_waves
is_first_thread_in_wave =
in_wave_id .==. 0
wave_not_skipped =
(wave_id .&. (2 * Imp.var skip_waves int32 - 1)) .==. 0
apply_in_cross_wave_iteration =
arg_in_bounds .&&. is_first_thread_in_wave .&&. wave_not_skipped
cross_wave_reductions = do
skip_waves <-- 1
sWhile doing_cross_wave_reductions $ do
barrier
offset <-- Imp.var skip_waves int32 * wave_size
sWhen apply_in_cross_wave_iteration
do_reduce
skip_waves <-- Imp.var skip_waves int32 * 2
in_wave_reductions
cross_wave_reductions
where local_tid = kernelLocalThreadId constants
global_tid = kernelGlobalThreadId constants
barrier
| all primType $ lambdaReturnType lam = sOp Imp.LocalBarrier
| otherwise = sOp Imp.GlobalBarrier
readReduceArgument param arr
| Prim _ <- paramType param = do
let i = local_tid + ImpGen.varIndex offset
ImpGen.copyDWIM (paramName param) [] (Var arr) [i]
| otherwise = do
let i = global_tid + ImpGen.varIndex offset
ImpGen.copyDWIM (paramName param) [] (Var arr) [i]
writeReduceOpResult param arr
| Prim _ <- paramType param =
ImpGen.copyDWIM arr [local_tid] (Var $ paramName param) []
| otherwise =
return ()
groupScan :: KernelConstants
-> Maybe (Imp.Exp -> Imp.Exp -> Imp.Exp)
-> Imp.Exp
-> Lambda InKernel
-> [VName]
-> ImpGen.ImpM InKernel Imp.KernelOp ()
groupScan constants seg_flag w lam arrs = do
when (any (not . primType . paramType) $ lambdaParams lam) $
compilerLimitationS "Cannot compile parallel scans with array element type."
renamed_lam <- renameLambda lam
acc_local_mem <- flip zip (repeat ()) <$>
mapM (fmap (ImpGen.memLocationName . ImpGen.entryArrayLocation) .
ImpGen.lookupArray) arrs
let ltid = kernelLocalThreadId constants
(lam_i, other_index_param, actual_params) =
partitionChunkedKernelLambdaParameters $ lambdaParams lam
(x_params, y_params) = splitAt (length arrs) actual_params
ImpGen.dLParams (lambdaParams lam++lambdaParams renamed_lam)
lam_i <-- ltid
-- The scan works by splitting the group into blocks, which are
-- scanned separately. Typically, these blocks are smaller than
-- the lockstep width, which enables barrier-free execution inside
-- them.
--
-- We hardcode the block size here. The only requirement is that
-- it should not be less than the square root of the group size.
-- With 32, we will work on groups of size 1024 or smaller, which
-- fits every device Troels has seen. Still, it would be nicer if
-- it were a runtime parameter. Some day.
let block_size = Imp.ValueExp $ IntValue $ Int32Value 32
simd_width = kernelWaveSize constants
block_id = ltid `quot` block_size
in_block_id = ltid - block_id * block_size
doInBlockScan seg_flag' active = inBlockScan seg_flag' simd_width block_size active ltid acc_local_mem
ltid_in_bounds = ltid .<. w
doInBlockScan seg_flag ltid_in_bounds lam
sOp Imp.LocalBarrier
let last_in_block = in_block_id .==. block_size - 1
sComment "last thread of block 'i' writes its result to offset 'i'" $
sWhen (last_in_block .&&. ltid_in_bounds) $
zipWithM_ (writeParamToLocalMemory block_id) acc_local_mem y_params
sOp Imp.LocalBarrier
let is_first_block = block_id .==. 0
first_block_seg_flag = do
flag_true <- seg_flag
Just $ \from to ->
flag_true (from*block_size+block_size-1) (to*block_size+block_size-1)
ImpGen.comment
"scan the first block, after which offset 'i' contains carry-in for warp 'i+1'" $
doInBlockScan first_block_seg_flag (is_first_block .&&. ltid_in_bounds) renamed_lam
sOp Imp.LocalBarrier
let read_carry_in =
zipWithM_ (readParamFromLocalMemory
(paramName other_index_param) (block_id - 1))
x_params acc_local_mem
let op_to_y
| Nothing <- seg_flag =
ImpGen.compileBody' y_params $ lambdaBody lam
| Just flag_true <- seg_flag =
sUnless (flag_true (block_id*block_size-1) ltid) $
ImpGen.compileBody' y_params $ lambdaBody lam
write_final_result =
zipWithM_ (writeParamToLocalMemory ltid) acc_local_mem y_params
sComment "carry-in for every block except the first" $
sUnless (is_first_block .||. Imp.UnOpExp Not ltid_in_bounds) $ do
sComment "read operands" read_carry_in
sComment "perform operation" op_to_y
sComment "write final result" write_final_result
sOp Imp.LocalBarrier
sComment "restore correct values for first block" $
sWhen is_first_block write_final_result
sOp Imp.LocalBarrier
inBlockScan :: Maybe (Imp.Exp -> Imp.Exp -> Imp.Exp)
-> Imp.Exp
-> Imp.Exp
-> Imp.Exp
-> Imp.Exp
-> [(VName, t)]
-> Lambda InKernel
-> InKernelGen ()
inBlockScan seg_flag lockstep_width block_size active ltid acc_local_mem scan_lam = ImpGen.everythingVolatile $ do
skip_threads <- dPrim "skip_threads" int32
let in_block_thread_active =
Imp.var skip_threads int32 .<=. in_block_id
(scan_lam_i, other_index_param, actual_params) =
partitionChunkedKernelLambdaParameters $ lambdaParams scan_lam
(x_params, y_params) =
splitAt (length actual_params `div` 2) actual_params
read_operands =
zipWithM_ (readParamFromLocalMemory (paramName other_index_param) $
ltid - Imp.var skip_threads int32)
x_params acc_local_mem
-- Set initial y values
sWhen active $
zipWithM_ (readParamFromLocalMemory scan_lam_i ltid)
y_params acc_local_mem
let op_to_y
| Nothing <- seg_flag =
ImpGen.compileBody' y_params $ lambdaBody scan_lam
| Just flag_true <- seg_flag =
sUnless (flag_true (ltid-Imp.var skip_threads int32) ltid) $
ImpGen.compileBody' y_params $ lambdaBody scan_lam
write_operation_result =
zipWithM_ (writeParamToLocalMemory ltid) acc_local_mem y_params
maybeLocalBarrier = sWhen (lockstep_width .<=. Imp.var skip_threads int32) $
sOp Imp.LocalBarrier
sComment "in-block scan (hopefully no barriers needed)" $ do
skip_threads <-- 1
sWhile (Imp.var skip_threads int32 .<. block_size) $ do
sWhen (in_block_thread_active .&&. active) $ do
sComment "read operands" read_operands
sComment "perform operation" op_to_y
maybeLocalBarrier
sWhen (in_block_thread_active .&&. active) $
sComment "write result" write_operation_result
maybeLocalBarrier
skip_threads <-- Imp.var skip_threads int32 * 2
where block_id = ltid `quot` block_size
in_block_id = ltid - block_id * block_size
compileKernelStms :: KernelConstants -> [Stm InKernel]
-> InKernelGen a
-> InKernelGen a
compileKernelStms constants ungrouped_bnds m =
compileGroupedKernelStms' $ groupStmsByGuard constants ungrouped_bnds
where compileGroupedKernelStms' [] = m
compileGroupedKernelStms' ((g, bnds):rest_bnds) = do
ImpGen.dScopes (map ((Just . stmExp) &&& (castScope . scopeOf)) bnds)
protect g $ mapM_ compileKernelStm bnds
compileGroupedKernelStms' rest_bnds
protect Nothing body_m =
body_m
protect (Just (Imp.ValueExp (BoolValue True))) body_m =
body_m
protect (Just g) body_m =
sWhen g $ allThreads constants body_m
compileKernelStm (Let pat _ e) = ImpGen.compileExp pat e
groupStmsByGuard :: KernelConstants
-> [Stm InKernel]
-> [(Maybe Imp.Exp, [Stm InKernel])]
groupStmsByGuard constants bnds =
map collapse $ groupBy sameGuard $ zip (map bindingGuard bnds) bnds
where bindingGuard (Let _ _ Op{}) = Nothing
bindingGuard _ = Just $ kernelThreadActive constants
sameGuard (g1, _) (g2, _) = g1 == g2
collapse [] =
(Nothing, [])
collapse l@((g,_):_) =
(g, map snd l)
computeMapKernelGroups :: Imp.Exp -> CallKernelGen (Imp.Exp, Imp.Exp)
computeMapKernelGroups kernel_size = do
group_size <- dPrim "group_size" int32
fname <- asks ImpGen.envFunction
let group_size_var = Imp.var group_size int32
group_size_key = keyWithEntryPoint fname $ nameFromString $ pretty group_size
sOp $ Imp.GetSize group_size group_size_key Imp.SizeGroup
num_groups <- dPrimV "num_groups" $ kernel_size `quotRoundingUp` Imp.ConvOpExp (SExt Int32 Int32) group_size_var
return (Imp.var group_size int32, Imp.var num_groups int32)
simpleKernelConstants :: Imp.Exp -> String
-> CallKernelGen (KernelConstants, ImpGen.ImpM InKernel Imp.KernelOp ())
simpleKernelConstants kernel_size desc = do
thread_gtid <- newVName $ desc ++ "_gtid"
thread_ltid <- newVName $ desc ++ "_ltid"
group_id <- newVName $ desc ++ "_gid"
(group_size, num_groups) <- computeMapKernelGroups kernel_size
let set_constants = do
dPrim_ thread_gtid int32
dPrim_ thread_ltid int32
dPrim_ group_id int32
sOp (Imp.GetGlobalId thread_gtid 0)
sOp (Imp.GetLocalId thread_ltid 0)
sOp (Imp.GetGroupId group_id 0)
return (KernelConstants
(Imp.var thread_gtid int32) (Imp.var thread_ltid int32) (Imp.var group_id int32)
thread_gtid thread_ltid group_id
group_size num_groups (group_size*num_groups) 0
[] (Imp.var thread_gtid int32 .<. kernel_size) mempty,
set_constants)
sKernel :: KernelConstants -> String -> ImpGen.ImpM InKernel Imp.KernelOp a -> CallKernelGen ()
sKernel constants name m = do
body <- makeAllMemoryGlobal $
ImpGen.subImpM_ (inKernelOperations constants) m
(uses, local_memory) <- computeKernelUses body mempty
ImpGen.emit $ Imp.Op $ Imp.CallKernel Imp.Kernel
{ Imp.kernelBody = body
, Imp.kernelLocalMemory = local_memory
, Imp.kernelUses = uses
, Imp.kernelNumGroups = [kernelNumGroups constants]
, Imp.kernelGroupSize = [kernelGroupSize constants]
, Imp.kernelName =
nameFromString $ name ++ "_" ++ show (baseTag $ kernelGlobalThreadIdVar constants)
}
-- | Perform a Replicate with a kernel.
sReplicate :: VName -> Shape -> SubExp
-> CallKernelGen ()
sReplicate arr (Shape ds) se = do
t <- subExpType se
dims <- mapM ImpGen.compileSubExp $ ds ++ arrayDims t
(constants, set_constants) <-
simpleKernelConstants (product dims) "replicate"
let is' = unflattenIndex dims $ kernelGlobalThreadId constants
sKernel constants "replicate" $ do
set_constants
sWhen (kernelThreadActive constants) $
ImpGen.copyDWIM arr is' se $ drop (length ds) is'
-- | Perform an Iota with a kernel.
sIota :: VName -> Imp.Exp -> Imp.Exp -> Imp.Exp -> IntType
-> CallKernelGen ()
sIota arr n x s et = do
destloc <- ImpGen.entryArrayLocation <$> ImpGen.lookupArray arr
(constants, set_constants) <- simpleKernelConstants n "iota"
sKernel constants "iota" $ do
set_constants
let gtid = kernelGlobalThreadId constants
sWhen (kernelThreadActive constants) $ do
(destmem, destspace, destidx) <-
ImpGen.fullyIndexArray' destloc [gtid] (IntType et)
ImpGen.emit $
Imp.Write destmem destidx (IntType et) destspace Imp.Nonvolatile $
Imp.ConvOpExp (SExt Int32 et) gtid * s + x
sCopy :: PrimType
-> ImpGen.MemLocation
-> ImpGen.MemLocation
-> Imp.Count Imp.Elements
-> CallKernelGen ()
sCopy bt
destloc@(ImpGen.MemLocation destmem _ _)
srcloc@(ImpGen.MemLocation srcmem srcshape _)
n = do
-- Note that the shape of the destination and the source are
-- necessarily the same.
let shape = map Imp.sizeToExp srcshape
shape_se = map (Imp.innerExp . ImpGen.dimSizeToExp) srcshape
kernel_size = Imp.innerExp n * product (drop 1 shape)
(constants, set_constants) <- simpleKernelConstants kernel_size "copy"
sKernel constants "copy" $ do
set_constants
let gtid = kernelGlobalThreadId constants
dest_is = unflattenIndex shape_se gtid
src_is = dest_is
(_, destspace, destidx) <- ImpGen.fullyIndexArray' destloc dest_is bt
(_, srcspace, srcidx) <- ImpGen.fullyIndexArray' srcloc src_is bt
sWhen (gtid .<. kernel_size) $ ImpGen.emit $
Imp.Write destmem destidx bt destspace Imp.Nonvolatile $
Imp.index srcmem srcidx bt srcspace Imp.Nonvolatile