Changes between Version 7 and Version 8 of DataParallel/Vectorisation/TypeVectorisation
 Timestamp:
 May 29, 2007 8:22:36 AM (10 years ago)
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DataParallel/Vectorisation/TypeVectorisation
v7 v8 1 1 == Type Vectorisation == 2 2 3 The transformation of types includes both closure conversion and the pairing of scalar with lifted computations.3 The transformation of types includes the generation of lifted types, the pairing of scalar with lifted computations, and closure conversion. 4 4 5 5 === Unboxed types === 6 6 7 Unboxed types and functions defined in `GHC.Prim` need to be treated specially during vectorisation. This is as we cannot have `PA` instances for unboxed types and the transformation needs to know which functions from `GHC.Prim` can be safely parallelised (e.g., its fine to run many ` +#` in parallel, whereas this is not really advisable for calls to sideeffecting RTS functions). Indeed, we might regard unboxed types and functions from `GHC.Prim` as the place where we make the transition from implementing vectorisation decisions in package ndp to hardcoding them into the compiler. It is probably a good idea to eventually move as much as possible of the hardcoded information into `primops.txt.pp`, but for the moment, we simply hardcode everything in the modules in `vectorise/`.7 Unboxed types and functions defined in `GHC.Prim` need to be treated specially during vectorisation. This is as we cannot have `PA` instances for unboxed types and the transformation needs to know which functions from `GHC.Prim` can be safely parallelised (e.g., its fine to run many `(+#)` in parallel, whereas this is not really advisable for calls to sideeffecting RTS functions). Indeed, we might regard unboxed types and functions from `GHC.Prim` as the place where we make the transition from implementing vectorisation decisions in package ndp to hardcoding them into the compiler. It is probably a good idea to eventually move as much as possible of the hardcoded information into `primops.txt.pp`, but for the moment, we simply hardcode everything in the modules in `vectorise/`. 8 8 9 To treat unboxed type properly, we cannot simply use the type constructor `PArr` wherever we need a flattened array; instead, we define a type translation 10 {{{ 11 Int#^ = UArr Int 12 Float#^ = UArr Float 13 Double#^ = UArr Double 14 <and so on for other unboxed types> 15 t^ = PArr t* 16 }}} 9 To treat unboxed types properly, we cannot simply use the type constructor `PArr` wherever we need a flattened array; instead, we define a type translation `t^` that treats unboxed types specially; e.g., `Int#^ = UArr Int`. 17 10 18 11 We need to represent functions whose argument and/or result type are unboxed different from functions over boxed types. The reason is the nonstandard kinding rule implemented in GHC for `(>)`, which allows that the two argument type variables are instantiated to unboxed values iff the application of `(>)` is saturated. We can't defined a second type constructor with that property unless we extend the `TypeRep.Type` representation. We also can't simply use a type synonym for a vectorised type function constructor, because we must be able to partially apply it. 19 12 20 === Transformation rules === 13 14 === Vectorisation === 21 15 22 16 TODO: 23 * Be careful that `VFun (t1* > t2*)` and `t1* > t2*` includes `PArr t1` and `PArr t2*`; so, we can only use them if we have `PA` instances for these types.17 * Types `t1* :> t2*` and `t1* :=> t2*` include `PArr t1*` and `PArr t2*`; so, we can only use them if we have `PA` instances for these types. 24 18 25 19 The type transformation rules achieve two goals: (1) they replace original type constructors and variables by their vectorised variants, where those are available, and (2) they alter the representation of functions: … … 27 21 T* = T_V , if T_V exists 28 22 = T , otherwise 29 a* = a _v23 a* = a 30 24 (t1 > t2)* 31 25  isUbxFun (t1>t2) = (t1* > t2*) : (t1^ > t2^) 32 26  otherwise = t1* :> t2* 33 27 (t1 t2)* = t1* t2* 34 (forall a.t)* = forall a _v.t*28 (forall a.t)* = forall a.t* 35 29 }}} 36 We need to distinguish between saturated function space applications involving unboxed types and those that don't, as we need to remain to be compatible with `(>_v) = (:>)`. 30 When encountering saturated function space applications , we need to distinguish those that involve unboxed types, as we need to remain to be compatible with `(>_v) = (:>)` for boxed types. (In other words, the distinction cannot simply be based on whether an application is saturated or not, it really needs to be one the basis of the kinds of types involved.) 31 32 ==== Fixed data constructor mapping ==== 33 34 {{{ 35 (>_v) = (:>) 36 [::]_v = PArr 37 }}} 37 38 38 39 40 === Lifting === 39 41 42 The lifting of types into vector space is, for all boxed monotypes, denoted by the array family constructor `PArr`. However, need to handle the lifting of unboxed types and the extension of signatures with `PA` dictionaries explicitly: 40 43 {{{ 41  OLD 42 T* = T_V , if T_V exists 43 = T , otherwise 44 a* = a_v 45 (t1 > t2)* = ( t1* > t2*, , if kindOf t1 == # 46 [:t1* > t2*:]) or kindOf t2 == # 47 = ( t1* :> t2*, , otherwise 48 [:t1* :> t2*:]) 49 (t1 t2)* = t1* t2* 50 (forall a.t)* = forall a_v.t* 44 Int#^ = UArr Int 45 Float#^ = UArr Float 46 Double#^ = UArr Double 47 ..and so on for other unboxed types.. 48 49 (forall a.t)^ = forall a. PA a > t^ 50 t^ = PArr t* 51 51 }}} 52 As a consequence, we cannot have impredicative instantiations of `[::]`, but this doesn't seem to be a significant restriction. 53 54 55 === `PArr` family instances === 56 57 Remember that `PArr` is defined over vectorised types: 58 {{{ 59 newtype instance PArr (f : (arr > brr)) 60 = PArrUFun (f : (ACls arr brr)) 61 newtype instance PArr (a :> b) = PArrFun (a :=> b) 62 }}}