diff options
Diffstat (limited to 'compiler')
| -rw-r--r-- | compiler/specialise/SpecConstr.lhs | 56 |
1 files changed, 31 insertions, 25 deletions
diff --git a/compiler/specialise/SpecConstr.lhs b/compiler/specialise/SpecConstr.lhs index c4b46aa5b2..44dc6f00ef 100644 --- a/compiler/specialise/SpecConstr.lhs +++ b/compiler/specialise/SpecConstr.lhs @@ -1,6 +1,6 @@ -ToDo [Nov 2010] +ToDo [Oct 2013] ~~~~~~~~~~~~~~~ -1. Use a library type rather than an annotation for ForceSpecConstr +1. Nuke ForceSpecConstr for good (it is subsumed by GHC.Types.SPEC in ghc-prim) 2. Nuke NoSpecConstr % @@ -56,7 +56,7 @@ import Data.List import TyCon ( TyCon, tyConName ) import PrelNames ( specTyConName ) --- See Note [SpecConstrAnnotation] +-- See Note [Forcing specialisation] #ifndef GHCI type SpecConstrAnnotation = () #else @@ -423,28 +423,40 @@ But fspec doesn't have decent strictness info. As it happened, and hence f. But now f's strictness is less than its arity, which breaks an invariant. -Note [SpecConstrAnnotation] -~~~~~~~~~~~~~~~~~~~~~~~~~~~ -SpecConstrAnnotation is defined in GHC.Exts, and is only guaranteed to -be available in stage 2 (well, until the bootstrap compiler can be -guaranteed to have it) - -So we define it to be () in stage1 (ie when GHCI is undefined), and -'#ifdef' out the code that uses it. - -See also Note [Forcing specialisation] Note [Forcing specialisation] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -With stream fusion and in other similar cases, we want to fully specialise -some (but not necessarily all!) loops regardless of their size and the -number of specialisations. We allow a library to specify this by annotating -a type with ForceSpecConstr and then adding a parameter of that type to the -loop. Here is a (simplified) example from the vector library: + +With stream fusion and in other similar cases, we want to fully +specialise some (but not necessarily all!) loops regardless of their +size and the number of specialisations. + +We allow a library to do this, in one of two ways (one which is +deprecated): + + 1) Add a parameter of type GHC.Types.SPEC (from ghc-prim) to the loop body. + + 2) (Deprecated) Annotate a type with ForceSpecConstr from GHC.Exts, + and then add *that* type as a parameter to the loop body + +The reason #2 is deprecated is because it requires GHCi, which isn't +available for things like a cross compiler using stage1. + +Here's a (simplified) example from the `vector` package. You may bring +the special 'force specialization' type into scope by saying: + + import GHC.Types (SPEC(..)) + +or by defining your own type (again, deprecated): data SPEC = SPEC | SPEC2 {-# ANN type SPEC ForceSpecConstr #-} +(Note this is the exact same definition of GHC.Types.SPEC, just +without the annotation.) + +After that, you say: + foldl :: (a -> b -> a) -> a -> Stream b -> a {-# INLINE foldl #-} foldl f z (Stream step s _) = foldl_loop SPEC z s @@ -494,12 +506,6 @@ can be used in Stream states and (c) some types are fixed by the user (e.g., the accumulator here) but we still want to specialise as much as possible. -ForceSpecConstr is done by way of an annotation: - data SPEC = SPEC | SPEC2 - {-# ANN type SPEC ForceSpecConstr #-} -But SPEC is the *only* type so annotated, so it'd be better to -use a particular library type. - Alternatives to ForceSpecConstr ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Instead of giving the loop an extra argument of type SPEC, we @@ -906,7 +912,7 @@ decreaseSpecCount env n_specs -- See Note [Avoiding exponential blowup] --------------------------------------------------- --- See Note [SpecConstrAnnotation] +-- See Note [Forcing specialisation] ignoreType :: ScEnv -> Type -> Bool ignoreDataCon :: ScEnv -> DataCon -> Bool forceSpecBndr :: ScEnv -> Var -> Bool |