%
% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
%
\section[SpecConstr]{Specialise over constructors}
\begin{code}
module SpecConstr(
specConstrProgram
#ifdef GHCI
, SpecConstrAnnotation(..)
#endif
) where
#include "HsVersions.h"
import CoreSyn
import CoreSubst
import CoreUtils
import CoreUnfold ( couldBeSmallEnoughToInline )
import CoreFVs ( exprsFreeVars )
import CoreMonad
import HscTypes ( ModGuts(..) )
import WwLib ( mkWorkerArgs )
import DataCon
import Coercion
import Rules
import Type hiding( substTy )
import Id
import MkCore ( mkImpossibleExpr )
import Var
import VarEnv
import VarSet
import Name
import BasicTypes
import DynFlags ( DynFlags(..) )
import StaticFlags ( opt_PprStyle_Debug )
import Maybes ( orElse, catMaybes, isJust, isNothing )
import Demand
import DmdAnal ( both )
import Serialized ( deserializeWithData )
import Util
import UniqSupply
import Outputable
import FastString
import UniqFM
import MonadUtils
import Control.Monad ( zipWithM )
import Data.List
#ifndef GHCI
type SpecConstrAnnotation = ()
#else
import Literal ( literalType )
import TyCon ( TyCon )
import GHC.Exts( SpecConstrAnnotation(..) )
#endif
\end{code}
-----------------------------------------------------
Game plan
-----------------------------------------------------
Consider
drop n [] = []
drop 0 xs = []
drop n (x:xs) = drop (n-1) xs
After the first time round, we could pass n unboxed. This happens in
numerical code too. Here's what it looks like in Core:
drop n xs = case xs of
[] -> []
(y:ys) -> case n of
I# n# -> case n# of
0 -> []
_ -> drop (I# (n# -# 1#)) xs
Notice that the recursive call has an explicit constructor as argument.
Noticing this, we can make a specialised version of drop
RULE: drop (I# n#) xs ==> drop' n# xs
drop' n# xs = let n = I# n# in ...orig RHS...
Now the simplifier will apply the specialisation in the rhs of drop', giving
drop' n# xs = case xs of
[] -> []
(y:ys) -> case n# of
0 -> []
_ -> drop (n# -# 1#) xs
Much better!
We'd also like to catch cases where a parameter is carried along unchanged,
but evaluated each time round the loop:
f i n = if i>0 || i>n then i else f (i*2) n
Here f isn't strict in n, but we'd like to avoid evaluating it each iteration.
In Core, by the time we've w/wd (f is strict in i) we get
f i# n = case i# ># 0 of
False -> I# i#
True -> case n of n' { I# n# ->
case i# ># n# of
False -> I# i#
True -> f (i# *# 2#) n'
At the call to f, we see that the argument, n is know to be (I# n#),
and n is evaluated elsewhere in the body of f, so we can play the same
trick as above.
Note [Reboxing]
~~~~~~~~~~~~~~~
We must be careful not to allocate the same constructor twice. Consider
f p = (...(case p of (a,b) -> e)...p...,
...let t = (r,s) in ...t...(f t)...)
At the recursive call to f, we can see that t is a pair. But we do NOT want
to make a specialised copy:
f' a b = let p = (a,b) in (..., ...)
because now t is allocated by the caller, then r and s are passed to the
recursive call, which allocates the (r,s) pair again.
This happens if
(a) the argument p is used in other than a case-scrutinsation way.
(b) the argument to the call is not a 'fresh' tuple; you have to
look into its unfolding to see that it's a tuple
Hence the "OR" part of Note [Good arguments] below.
ALTERNATIVE 2: pass both boxed and unboxed versions. This no longer saves
allocation, but does perhaps save evals. In the RULE we'd have
something like
f (I# x#) = f' (I# x#) x#
If at the call site the (I# x) was an unfolding, then we'd have to
rely on CSE to eliminate the duplicate allocation.... This alternative
doesn't look attractive enough to pursue.
ALTERNATIVE 3: ignore the reboxing problem. The trouble is that
the conservative reboxing story prevents many useful functions from being
specialised. Example:
foo :: Maybe Int -> Int -> Int
foo (Just m) 0 = 0
foo x@(Just m) n = foo x (n-m)
Here the use of 'x' will clearly not require boxing in the specialised function.
The strictness analyser has the same problem, in fact. Example:
f p@(a,b) = ...
If we pass just 'a' and 'b' to the worker, it might need to rebox the
pair to create (a,b). A more sophisticated analysis might figure out
precisely the cases in which this could happen, but the strictness
analyser does no such analysis; it just passes 'a' and 'b', and hopes
for the best.
So my current choice is to make SpecConstr similarly aggressive, and
ignore the bad potential of reboxing.
Note [Good arguments]
~~~~~~~~~~~~~~~~~~~~~
So we look for
* A self-recursive function. Ignore mutual recursion for now,
because it's less common, and the code is simpler for self-recursion.
* EITHER
a) At a recursive call, one or more parameters is an explicit
constructor application
AND
That same parameter is scrutinised by a case somewhere in
the RHS of the function
OR
b) At a recursive call, one or more parameters has an unfolding
that is an explicit constructor application
AND
That same parameter is scrutinised by a case somewhere in
the RHS of the function
AND
Those are the only uses of the parameter (see Note [Reboxing])
What to abstract over
~~~~~~~~~~~~~~~~~~~~~
There's a bit of a complication with type arguments. If the call
site looks like
f p = ...f ((:) [a] x xs)...
then our specialised function look like
f_spec x xs = let p = (:) [a] x xs in ....as before....
This only makes sense if either
a) the type variable 'a' is in scope at the top of f, or
b) the type variable 'a' is an argument to f (and hence fs)
Actually, (a) may hold for value arguments too, in which case
we may not want to pass them. Supose 'x' is in scope at f's
defn, but xs is not. Then we'd like
f_spec xs = let p = (:) [a] x xs in ....as before....
Similarly (b) may hold too. If x is already an argument at the
call, no need to pass it again.
Finally, if 'a' is not in scope at the call site, we could abstract
it as we do the term variables:
f_spec a x xs = let p = (:) [a] x xs in ...as before...
So the grand plan is:
* abstract the call site to a constructor-only pattern
e.g. C x (D (f p) (g q)) ==> C s1 (D s2 s3)
* Find the free variables of the abstracted pattern
* Pass these variables, less any that are in scope at
the fn defn. But see Note [Shadowing] below.
NOTICE that we only abstract over variables that are not in scope,
so we're in no danger of shadowing variables used in "higher up"
in f_spec's RHS.
Note [Shadowing]
~~~~~~~~~~~~~~~~
In this pass we gather up usage information that may mention variables
that are bound between the usage site and the definition site; or (more
seriously) may be bound to something different at the definition site.
For example:
f x = letrec g y v = let x = ...
in ...(g (a,b) x)...
Since 'x' is in scope at the call site, we may make a rewrite rule that
looks like
RULE forall a,b. g (a,b) x = ...
But this rule will never match, because it's really a different 'x' at
the call site -- and that difference will be manifest by the time the
simplifier gets to it. [A worry: the simplifier doesn't *guarantee*
no-shadowing, so perhaps it may not be distinct?]
Anyway, the rule isn't actually wrong, it's just not useful. One possibility
is to run deShadowBinds before running SpecConstr, but instead we run the
simplifier. That gives the simplest possible program for SpecConstr to
chew on; and it virtually guarantees no shadowing.
Note [Specialising for constant parameters]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
This one is about specialising on a *constant* (but not necessarily
constructor) argument
foo :: Int -> (Int -> Int) -> Int
foo 0 f = 0
foo m f = foo (f m) (+1)
It produces
lvl_rmV :: GHC.Base.Int -> GHC.Base.Int
lvl_rmV =
\ (ds_dlk :: GHC.Base.Int) ->
case ds_dlk of wild_alH { GHC.Base.I# x_alG ->
GHC.Base.I# (GHC.Prim.+# x_alG 1)
T.$wfoo :: GHC.Prim.Int# -> (GHC.Base.Int -> GHC.Base.Int) ->
GHC.Prim.Int#
T.$wfoo =
\ (ww_sme :: GHC.Prim.Int#) (w_smg :: GHC.Base.Int -> GHC.Base.Int) ->
case ww_sme of ds_Xlw {
__DEFAULT ->
case w_smg (GHC.Base.I# ds_Xlw) of w1_Xmo { GHC.Base.I# ww1_Xmz ->
T.$wfoo ww1_Xmz lvl_rmV
};
0 -> 0
}
The recursive call has lvl_rmV as its argument, so we could create a specialised copy
with that argument baked in; that is, not passed at all. Now it can perhaps be inlined.
When is this worth it? Call the constant 'lvl'
- If 'lvl' has an unfolding that is a constructor, see if the corresponding
parameter is scrutinised anywhere in the body.
- If 'lvl' has an unfolding that is a inlinable function, see if the corresponding
parameter is applied (...to enough arguments...?)
Also do this is if the function has RULES?
Also
Note [Specialising for lambda parameters]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
foo :: Int -> (Int -> Int) -> Int
foo 0 f = 0
foo m f = foo (f m) (\n -> n-m)
This is subtly different from the previous one in that we get an
explicit lambda as the argument:
T.$wfoo :: GHC.Prim.Int# -> (GHC.Base.Int -> GHC.Base.Int) ->
GHC.Prim.Int#
T.$wfoo =
\ (ww_sm8 :: GHC.Prim.Int#) (w_sma :: GHC.Base.Int -> GHC.Base.Int) ->
case ww_sm8 of ds_Xlr {
__DEFAULT ->
case w_sma (GHC.Base.I# ds_Xlr) of w1_Xmf { GHC.Base.I# ww1_Xmq ->
T.$wfoo
ww1_Xmq
(\ (n_ad3 :: GHC.Base.Int) ->
case n_ad3 of wild_alB { GHC.Base.I# x_alA ->
GHC.Base.I# (GHC.Prim.-# x_alA ds_Xlr)
})
};
0 -> 0
}
I wonder if SpecConstr couldn't be extended to handle this? After all,
lambda is a sort of constructor for functions and perhaps it already
has most of the necessary machinery?
Furthermore, there's an immediate win, because you don't need to allocate the lamda
at the call site; and if perchance it's called in the recursive call, then you
may avoid allocating it altogether. Just like for constructors.
Looks cool, but probably rare...but it might be easy to implement.
Note [SpecConstr for casts]
~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider
data family T a :: *
data instance T Int = T Int
foo n = ...
where
go (T 0) = 0
go (T n) = go (T (n-1))
The recursive call ends up looking like
go (T (I# ...) `cast` g)
So we want to spot the construtor application inside the cast.
That's why we have the Cast case in argToPat
Note [Local recursive groups]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
For a *local* recursive group, we can see all the calls to the
function, so we seed the specialisation loop from the calls in the
body, not from the calls in the RHS. Consider:
bar m n = foo n (n,n) (n,n) (n,n) (n,n)
where
foo n p q r s
| n == 0 = m
| n > 3000 = case p of { (p1,p2) -> foo (n-1) (p2,p1) q r s }
| n > 2000 = case q of { (q1,q2) -> foo (n-1) p (q2,q1) r s }
| n > 1000 = case r of { (r1,r2) -> foo (n-1) p q (r2,r1) s }
| otherwise = case s of { (s1,s2) -> foo (n-1) p q r (s2,s1) }
If we start with the RHSs of 'foo', we get lots and lots of specialisations,
most of which are not needed. But if we start with the (single) call
in the rhs of 'bar' we get exactly one fully-specialised copy, and all
the recursive calls go to this fully-specialised copy. Indeed, the original
function is later collected as dead code. This is very important in
specialising the loops arising from stream fusion, for example in NDP where
we were getting literally hundreds of (mostly unused) specialisations of
a local function.
Note [Do not specialise diverging functions]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Specialising a function that just diverges is a waste of code.
Furthermore, it broke GHC (simpl014) thus:
{-# STR Sb #-}
f = \x. case x of (a,b) -> f x
If we specialise f we get
f = \x. case x of (a,b) -> fspec a b
But fspec doesn't have decent strictnes info. As it happened,
(f x) :: IO t, so the state hack applied and we eta expanded fspec,
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:
data SPEC = SPEC | SPEC2
{-# ANN type SPEC ForceSpecConstr #-}
foldl :: (a -> b -> a) -> a -> Stream b -> a
{-# INLINE foldl #-}
foldl f z (Stream step s _) = foldl_loop SPEC z s
where
foldl_loop SPEC z s = case step s of
Yield x s' -> foldl_loop SPEC (f z x) s'
Skip -> foldl_loop SPEC z s'
Done -> z
SpecConstr will spot the SPEC parameter and always fully specialise
foldl_loop. Note that we can't just annotate foldl_loop since it isn't a
top-level function but even if we could, inlining etc. could easily drop the
annotation. We also have to prevent the SPEC argument from being removed by
w/w which is why SPEC is a sum type. This is all quite ugly; we ought to come
up with a better design.
ForceSpecConstr arguments are spotted in scExpr' and scTopBinds which then set
force_spec to True when calling specLoop. This flag makes specLoop and
specialise ignore specConstrCount and specConstrThreshold when deciding
whether to specialise a function.
-----------------------------------------------------
Stuff not yet handled
-----------------------------------------------------
Here are notes arising from Roman's work that I don't want to lose.
Example 1
~~~~~~~~~
data T a = T !a
foo :: Int -> T Int -> Int
foo 0 t = 0
foo x t | even x = case t of { T n -> foo (x-n) t }
| otherwise = foo (x-1) t
SpecConstr does no specialisation, because the second recursive call
looks like a boxed use of the argument. A pity.
$wfoo_sFw :: GHC.Prim.Int# -> T.T GHC.Base.Int -> GHC.Prim.Int#
$wfoo_sFw =
\ (ww_sFo [Just L] :: GHC.Prim.Int#) (w_sFq [Just L] :: T.T GHC.Base.Int) ->
case ww_sFo of ds_Xw6 [Just L] {
__DEFAULT ->
case GHC.Prim.remInt# ds_Xw6 2 of wild1_aEF [Dead Just A] {
__DEFAULT -> $wfoo_sFw (GHC.Prim.-# ds_Xw6 1) w_sFq;
0 ->
case w_sFq of wild_Xy [Just L] { T.T n_ad5 [Just U(L)] ->
case n_ad5 of wild1_aET [Just A] { GHC.Base.I# y_aES [Just L] ->
$wfoo_sFw (GHC.Prim.-# ds_Xw6 y_aES) wild_Xy
} } };
0 -> 0
Example 2
~~~~~~~~~
data a :*: b = !a :*: !b
data T a = T !a
foo :: (Int :*: T Int) -> Int
foo (0 :*: t) = 0
foo (x :*: t) | even x = case t of { T n -> foo ((x-n) :*: t) }
| otherwise = foo ((x-1) :*: t)
Very similar to the previous one, except that the parameters are now in
a strict tuple. Before SpecConstr, we have
$wfoo_sG3 :: GHC.Prim.Int# -> T.T GHC.Base.Int -> GHC.Prim.Int#
$wfoo_sG3 =
\ (ww_sFU [Just L] :: GHC.Prim.Int#) (ww_sFW [Just L] :: T.T
GHC.Base.Int) ->
case ww_sFU of ds_Xws [Just L] {
__DEFAULT ->
case GHC.Prim.remInt# ds_Xws 2 of wild1_aEZ [Dead Just A] {
__DEFAULT ->
case ww_sFW of tpl_B2 [Just L] { T.T a_sFo [Just A] ->
$wfoo_sG3 (GHC.Prim.-# ds_Xws 1) tpl_B2 -- $wfoo1
};
0 ->
case ww_sFW of wild_XB [Just A] { T.T n_ad7 [Just S(L)] ->
case n_ad7 of wild1_aFd [Just L] { GHC.Base.I# y_aFc [Just L] ->
$wfoo_sG3 (GHC.Prim.-# ds_Xws y_aFc) wild_XB -- $wfoo2
} } };
0 -> 0 }
We get two specialisations:
"SC:$wfoo1" [0] __forall {a_sFB :: GHC.Base.Int sc_sGC :: GHC.Prim.Int#}
Foo.$wfoo sc_sGC (Foo.T @ GHC.Base.Int a_sFB)
= Foo.$s$wfoo1 a_sFB sc_sGC ;
"SC:$wfoo2" [0] __forall {y_aFp :: GHC.Prim.Int# sc_sGC :: GHC.Prim.Int#}
Foo.$wfoo sc_sGC (Foo.T @ GHC.Base.Int (GHC.Base.I# y_aFp))
= Foo.$s$wfoo y_aFp sc_sGC ;
But perhaps the first one isn't good. After all, we know that tpl_B2 is
a T (I# x) really, because T is strict and Int has one constructor. (We can't
unbox the strict fields, becuase T is polymorphic!)
%************************************************************************
%* *
\subsection{Top level wrapper stuff}
%* *
%************************************************************************
\begin{code}
specConstrProgram :: ModGuts -> CoreM ModGuts
specConstrProgram guts
= do
dflags <- getDynFlags
us <- getUniqueSupplyM
annos <- getFirstAnnotations deserializeWithData guts
let binds' = fst $ initUs us (go (initScEnv dflags annos) (mg_binds guts))
return (guts { mg_binds = binds' })
where
go _ [] = return []
go env (bind:binds) = do (env', bind') <- scTopBind env bind
binds' <- go env' binds
return (bind' : binds')
\end{code}
%************************************************************************
%* *
\subsection{Environment: goes downwards}
%* *
%************************************************************************
\begin{code}
data ScEnv = SCE { sc_size :: Maybe Int,
sc_count :: Maybe Int,
sc_subst :: Subst,
sc_how_bound :: HowBoundEnv,
sc_vals :: ValueEnv,
sc_annotations :: UniqFM SpecConstrAnnotation
}
type InExpr = CoreExpr
type InVar = Var
type OutExpr = CoreExpr
type OutId = Id
type OutVar = Var
type HowBoundEnv = VarEnv HowBound
type ValueEnv = IdEnv Value
data Value = ConVal AltCon [CoreArg]
| LambdaVal
instance Outputable Value where
ppr (ConVal con args) = ppr con <+> interpp'SP args
ppr LambdaVal = ptext (sLit "<Lambda>")
initScEnv :: DynFlags -> UniqFM SpecConstrAnnotation -> ScEnv
initScEnv dflags anns
= SCE { sc_size = specConstrThreshold dflags,
sc_count = specConstrCount dflags,
sc_subst = emptySubst,
sc_how_bound = emptyVarEnv,
sc_vals = emptyVarEnv,
sc_annotations = anns }
data HowBound = RecFun
| RecArg
instance Outputable HowBound where
ppr RecFun = text "RecFun"
ppr RecArg = text "RecArg"
lookupHowBound :: ScEnv -> Id -> Maybe HowBound
lookupHowBound env id = lookupVarEnv (sc_how_bound env) id
scSubstId :: ScEnv -> Id -> CoreExpr
scSubstId env v = lookupIdSubst (text "scSubstId") (sc_subst env) v
scSubstTy :: ScEnv -> Type -> Type
scSubstTy env ty = substTy (sc_subst env) ty
zapScSubst :: ScEnv -> ScEnv
zapScSubst env = env { sc_subst = zapSubstEnv (sc_subst env) }
extendScInScope :: ScEnv -> [Var] -> ScEnv
extendScInScope env qvars = env { sc_subst = extendInScopeList (sc_subst env) qvars }
extendScSubst :: ScEnv -> Var -> OutExpr -> ScEnv
extendScSubst env var expr = env { sc_subst = extendSubst (sc_subst env) var expr }
extendScSubstList :: ScEnv -> [(Var,OutExpr)] -> ScEnv
extendScSubstList env prs = env { sc_subst = extendSubstList (sc_subst env) prs }
extendHowBound :: ScEnv -> [Var] -> HowBound -> ScEnv
extendHowBound env bndrs how_bound
= env { sc_how_bound = extendVarEnvList (sc_how_bound env)
[(bndr,how_bound) | bndr <- bndrs] }
extendBndrsWith :: HowBound -> ScEnv -> [Var] -> (ScEnv, [Var])
extendBndrsWith how_bound env bndrs
= (env { sc_subst = subst', sc_how_bound = hb_env' }, bndrs')
where
(subst', bndrs') = substBndrs (sc_subst env) bndrs
hb_env' = sc_how_bound env `extendVarEnvList`
[(bndr,how_bound) | bndr <- bndrs']
extendBndrWith :: HowBound -> ScEnv -> Var -> (ScEnv, Var)
extendBndrWith how_bound env bndr
= (env { sc_subst = subst', sc_how_bound = hb_env' }, bndr')
where
(subst', bndr') = substBndr (sc_subst env) bndr
hb_env' = extendVarEnv (sc_how_bound env) bndr' how_bound
extendRecBndrs :: ScEnv -> [Var] -> (ScEnv, [Var])
extendRecBndrs env bndrs = (env { sc_subst = subst' }, bndrs')
where
(subst', bndrs') = substRecBndrs (sc_subst env) bndrs
extendBndr :: ScEnv -> Var -> (ScEnv, Var)
extendBndr env bndr = (env { sc_subst = subst' }, bndr')
where
(subst', bndr') = substBndr (sc_subst env) bndr
extendValEnv :: ScEnv -> Id -> Maybe Value -> ScEnv
extendValEnv env _ Nothing = env
extendValEnv env id (Just cv) = env { sc_vals = extendVarEnv (sc_vals env) id cv }
extendCaseBndrs :: ScEnv -> OutExpr -> OutId -> AltCon -> [Var] -> (ScEnv, [Var])
extendCaseBndrs env scrut case_bndr con alt_bndrs
= (env2, alt_bndrs')
where
live_case_bndr = not (isDeadBinder case_bndr)
env1 | Var v <- scrut = extendValEnv env v cval
| otherwise = env
env2 | live_case_bndr = extendValEnv env1 case_bndr cval
| otherwise = env1
alt_bndrs' | case scrut of { Var {} -> True; _ -> live_case_bndr }
= map zap alt_bndrs
| otherwise
= alt_bndrs
cval = case con of
DEFAULT -> Nothing
LitAlt {} -> Just (ConVal con [])
DataAlt {} -> Just (ConVal con vanilla_args)
where
vanilla_args = map Type (tyConAppArgs (idType case_bndr)) ++
varsToCoreExprs alt_bndrs
zap v | isTyCoVar v = v
| otherwise = zapIdOccInfo v
decreaseSpecCount :: ScEnv -> Int -> ScEnv
decreaseSpecCount env n_specs
= env { sc_count = case sc_count env of
Nothing -> Nothing
Just n -> Just (n `div` (n_specs + 1)) }
ignoreType :: ScEnv -> Type -> Bool
ignoreAltCon :: ScEnv -> AltCon -> Bool
forceSpecBndr :: ScEnv -> Var -> Bool
#ifndef GHCI
ignoreType _ _ = False
ignoreAltCon _ _ = False
forceSpecBndr _ _ = False
#else /* GHCI */
ignoreAltCon env (DataAlt dc) = ignoreTyCon env (dataConTyCon dc)
ignoreAltCon env (LitAlt lit) = ignoreType env (literalType lit)
ignoreAltCon _ DEFAULT = panic "ignoreAltCon"
ignoreType env ty
= case splitTyConApp_maybe ty of
Just (tycon, _) -> ignoreTyCon env tycon
_ -> False
ignoreTyCon :: ScEnv -> TyCon -> Bool
ignoreTyCon env tycon
= lookupUFM (sc_annotations env) tycon == Just NoSpecConstr
forceSpecBndr env var = forceSpecFunTy env . snd . splitForAllTys . varType $ var
forceSpecFunTy :: ScEnv -> Type -> Bool
forceSpecFunTy env = any (forceSpecArgTy env) . fst . splitFunTys
forceSpecArgTy :: ScEnv -> Type -> Bool
forceSpecArgTy env ty
| Just ty' <- coreView ty = forceSpecArgTy env ty'
forceSpecArgTy env ty
| Just (tycon, tys) <- splitTyConApp_maybe ty
, tycon /= funTyCon
= lookupUFM (sc_annotations env) tycon == Just ForceSpecConstr
|| any (forceSpecArgTy env) tys
forceSpecArgTy _ _ = False
#endif /* GHCI */
\end{code}
Note [Add scrutinee to ValueEnv too]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider this:
case x of y
(a,b) -> case b of c
I# v -> ...(f y)...
By the time we get to the call (f y), the ValueEnv
will have a binding for y, and for c
y -> (a,b)
c -> I# v
BUT that's not enough! Looking at the call (f y) we
see that y is pair (a,b), but we also need to know what 'b' is.
So in extendCaseBndrs we must *also* add the binding
b -> I# v
else we lose a useful specialisation for f. This is necessary even
though the simplifier has systematically replaced uses of 'x' with 'y'
and 'b' with 'c' in the code. The use of 'b' in the ValueEnv came
from outside the case. See Trac #4908 for the live example.
Note [Avoiding exponential blowup]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The sc_count field of the ScEnv says how many times we are prepared to
duplicate a single function. But we must take care with recursive
specialiations. Consider
let $j1 = let $j2 = let $j3 = ...
in
...$j3...
in
...$j2...
in
...$j1...
If we specialise $j1 then in each specialisation (as well as the original)
we can specialise $j2, and similarly $j3. Even if we make just *one*
specialisation of each, becuase we also have the original we'll get 2^n
copies of $j3, which is not good.
So when recursively specialising we divide the sc_count by the number of
copies we are making at this level, including the original.
%************************************************************************
%* *
\subsection{Usage information: flows upwards}
%* *
%************************************************************************
\begin{code}
data ScUsage
= SCU {
scu_calls :: CallEnv,
scu_occs :: !(IdEnv ArgOcc)
}
type CallEnv = IdEnv [Call]
type Call = (ValueEnv, [CoreArg])
nullUsage :: ScUsage
nullUsage = SCU { scu_calls = emptyVarEnv, scu_occs = emptyVarEnv }
combineCalls :: CallEnv -> CallEnv -> CallEnv
combineCalls = plusVarEnv_C (++)
combineUsage :: ScUsage -> ScUsage -> ScUsage
combineUsage u1 u2 = SCU { scu_calls = combineCalls (scu_calls u1) (scu_calls u2),
scu_occs = plusVarEnv_C combineOcc (scu_occs u1) (scu_occs u2) }
combineUsages :: [ScUsage] -> ScUsage
combineUsages [] = nullUsage
combineUsages us = foldr1 combineUsage us
lookupOcc :: ScUsage -> OutVar -> (ScUsage, ArgOcc)
lookupOcc (SCU { scu_calls = sc_calls, scu_occs = sc_occs }) bndr
= (SCU {scu_calls = sc_calls, scu_occs = delVarEnv sc_occs bndr},
lookupVarEnv sc_occs bndr `orElse` NoOcc)
lookupOccs :: ScUsage -> [OutVar] -> (ScUsage, [ArgOcc])
lookupOccs (SCU { scu_calls = sc_calls, scu_occs = sc_occs }) bndrs
= (SCU {scu_calls = sc_calls, scu_occs = delVarEnvList sc_occs bndrs},
[lookupVarEnv sc_occs b `orElse` NoOcc | b <- bndrs])
data ArgOcc = NoOcc
| UnkOcc
| ScrutOcc (UniqFM [ArgOcc])
| BothOcc
instance Outputable ArgOcc where
ppr (ScrutOcc xs) = ptext (sLit "scrut-occ") <> ppr xs
ppr UnkOcc = ptext (sLit "unk-occ")
ppr BothOcc = ptext (sLit "both-occ")
ppr NoOcc = ptext (sLit "no-occ")
combineOcc :: ArgOcc -> ArgOcc -> ArgOcc
combineOcc NoOcc occ = occ
combineOcc occ NoOcc = occ
combineOcc (ScrutOcc xs) (ScrutOcc ys) = ScrutOcc (plusUFM_C combineOccs xs ys)
combineOcc _occ (ScrutOcc ys) = ScrutOcc ys
combineOcc (ScrutOcc xs) _occ = ScrutOcc xs
combineOcc UnkOcc UnkOcc = UnkOcc
combineOcc _ _ = BothOcc
combineOccs :: [ArgOcc] -> [ArgOcc] -> [ArgOcc]
combineOccs xs ys = zipWithEqual "combineOccs" combineOcc xs ys
setScrutOcc :: ScEnv -> ScUsage -> OutExpr -> ArgOcc -> ScUsage
setScrutOcc env usg (Cast e _) occ = setScrutOcc env usg e occ
setScrutOcc env usg (Note _ e) occ = setScrutOcc env usg e occ
setScrutOcc env usg (Var v) occ
| Just RecArg <- lookupHowBound env v = usg { scu_occs = extendVarEnv (scu_occs usg) v occ }
| otherwise = usg
setScrutOcc _env usg _other _occ
= usg
conArgOccs :: ArgOcc -> AltCon -> [ArgOcc]
conArgOccs (ScrutOcc fm) (DataAlt dc)
| Just pat_arg_occs <- lookupUFM fm dc
= [UnkOcc | _ <- dataConUnivTyVars dc] ++ pat_arg_occs
conArgOccs _other _con = repeat UnkOcc
\end{code}
%************************************************************************
%* *
\subsection{The main recursive function}
%* *
%************************************************************************
The main recursive function gathers up usage information, and
creates specialised versions of functions.
\begin{code}
scExpr, scExpr' :: ScEnv -> CoreExpr -> UniqSM (ScUsage, CoreExpr)
scExpr env e = scExpr' env e
scExpr' env (Var v) = case scSubstId env v of
Var v' -> return (varUsage env v' UnkOcc, Var v')
e' -> scExpr (zapScSubst env) e'
scExpr' env (Type t) = return (nullUsage, Type (scSubstTy env t))
scExpr' _ e@(Lit {}) = return (nullUsage, e)
scExpr' env (Note n e) = do (usg,e') <- scExpr env e
return (usg, Note n e')
scExpr' env (Cast e co) = do (usg, e') <- scExpr env e
return (usg, Cast e' (scSubstTy env co))
scExpr' env e@(App _ _) = scApp env (collectArgs e)
scExpr' env (Lam b e) = do let (env', b') = extendBndr env b
(usg, e') <- scExpr env' e
return (usg, Lam b' e')
scExpr' env (Case scrut b ty alts)
= do { (scrut_usg, scrut') <- scExpr env scrut
; case isValue (sc_vals env) scrut' of
Just (ConVal con args) -> sc_con_app con args scrut'
_other -> sc_vanilla scrut_usg scrut'
}
where
sc_con_app con args scrut'
= do { let (_, bs, rhs) = findAlt con alts
`orElse` (DEFAULT, [], mkImpossibleExpr (coreAltsType alts))
alt_env' = extendScSubstList env ((b,scrut') : bs `zip` trimConArgs con args)
; scExpr alt_env' rhs }
sc_vanilla scrut_usg scrut'
= do { let (alt_env,b') = extendBndrWith RecArg env b
; (alt_usgs, alt_occs, alts')
<- mapAndUnzip3M (sc_alt alt_env scrut' b') alts
; let (alt_usg, b_occ) = lookupOcc (combineUsages alt_usgs) b'
scrut_occ = foldr combineOcc b_occ alt_occs
scrut_usg' = setScrutOcc env scrut_usg scrut' scrut_occ
; return (alt_usg `combineUsage` scrut_usg',
Case scrut' b' (scSubstTy env ty) alts') }
sc_alt env scrut' b' (con,bs,rhs)
= do { let (env1, bs1) = extendBndrsWith RecArg env bs
(env2, bs2) = extendCaseBndrs env1 scrut' b' con bs1
; (usg,rhs') <- scExpr env2 rhs
; let (usg', arg_occs) = lookupOccs usg bs2
scrut_occ = case con of
DataAlt dc -> ScrutOcc (unitUFM dc arg_occs)
_ -> ScrutOcc emptyUFM
; return (usg', scrut_occ, (con, bs2, rhs')) }
scExpr' env (Let (NonRec bndr rhs) body)
| isTyCoVar bndr
= scExpr' (extendScSubst env bndr rhs) body
| otherwise
= do { let (body_env, bndr') = extendBndr env bndr
; (rhs_usg, rhs_info) <- scRecRhs env (bndr',rhs)
; let body_env2 = extendHowBound body_env [bndr'] RecFun
RI _ rhs' _ _ _ = rhs_info
body_env3 = extendValEnv body_env2 bndr' (isValue (sc_vals env) rhs')
; (body_usg, body') <- scExpr body_env3 body
; let force_spec = False
; (spec_usg, specs) <- specialise env force_spec
(scu_calls body_usg)
rhs_info
(SI [] 0 (Just rhs_usg))
; return (body_usg { scu_calls = scu_calls body_usg `delVarEnv` bndr' }
`combineUsage` spec_usg,
mkLets [NonRec b r | (b,r) <- specInfoBinds rhs_info specs] body')
}
scExpr' env (Let (Rec prs) body)
= do { let (bndrs,rhss) = unzip prs
(rhs_env1,bndrs') = extendRecBndrs env bndrs
rhs_env2 = extendHowBound rhs_env1 bndrs' RecFun
force_spec = any (forceSpecBndr env) bndrs'
; (rhs_usgs, rhs_infos) <- mapAndUnzipM (scRecRhs rhs_env2) (bndrs' `zip` rhss)
; (body_usg, body') <- scExpr rhs_env2 body
; (spec_usg, specs) <- specLoop rhs_env2 force_spec
(scu_calls body_usg) rhs_infos nullUsage
[SI [] 0 (Just usg) | usg <- rhs_usgs]
; let all_usg = spec_usg `combineUsage` body_usg
bind' = Rec (concat (zipWith specInfoBinds rhs_infos specs))
; return (all_usg { scu_calls = scu_calls all_usg `delVarEnvList` bndrs' },
Let bind' body') }
\end{code}
Note [Local let bindings]
~~~~~~~~~~~~~~~~~~~~~~~~~
It is not uncommon to find this
let $j = \x. in ...$j True...$j True...
Here $j is an arbitrary let-bound function, but it often comes up for
join points. We might like to specialise $j for its call patterns.
Notice the difference from a letrec, where we look for call patterns
in the *RHS* of the function. Here we look for call patterns in the
*body* of the let.
At one point I predicated this on the RHS mentioning the outer
recursive function, but that's not essential and might even be
harmful. I'm not sure.
\begin{code}
scApp :: ScEnv -> (InExpr, [InExpr]) -> UniqSM (ScUsage, CoreExpr)
scApp env (Var fn, args)
= ASSERT( not (null args) )
do { args_w_usgs <- mapM (scExpr env) args
; let (arg_usgs, args') = unzip args_w_usgs
arg_usg = combineUsages arg_usgs
; case scSubstId env fn of
fn'@(Lam {}) -> scExpr (zapScSubst env) (doBeta fn' args')
Var fn' -> return (arg_usg `combineUsage` fn_usg, mkApps (Var fn') args')
where
fn_usg = case lookupHowBound env fn' of
Just RecFun -> SCU { scu_calls = unitVarEnv fn' [(sc_vals env, args')],
scu_occs = emptyVarEnv }
Just RecArg -> SCU { scu_calls = emptyVarEnv,
scu_occs = unitVarEnv fn' (ScrutOcc emptyUFM) }
Nothing -> nullUsage
other_fn' -> return (arg_usg, mkApps other_fn' args') }
where
doBeta :: OutExpr -> [OutExpr] -> OutExpr
doBeta (Lam bndr body) (arg : args) = Let (NonRec bndr arg) (doBeta body args)
doBeta fn args = mkApps fn args
scApp env (other_fn, args)
= do { (fn_usg, fn') <- scExpr env other_fn
; (arg_usgs, args') <- mapAndUnzipM (scExpr env) args
; return (combineUsages arg_usgs `combineUsage` fn_usg, mkApps fn' args') }
scTopBind :: ScEnv -> CoreBind -> UniqSM (ScEnv, CoreBind)
scTopBind env (Rec prs)
| Just threshold <- sc_size env
, not force_spec
, not (all (couldBeSmallEnoughToInline threshold) rhss)
= do { let (rhs_env,bndrs') = extendRecBndrs env bndrs
; (_, rhss') <- mapAndUnzipM (scExpr rhs_env) rhss
; return (rhs_env, Rec (bndrs' `zip` rhss')) }
| otherwise
= do { let (rhs_env1,bndrs') = extendRecBndrs env bndrs
rhs_env2 = extendHowBound rhs_env1 bndrs' RecFun
; (rhs_usgs, rhs_infos) <- mapAndUnzipM (scRecRhs rhs_env2) (bndrs' `zip` rhss)
; let rhs_usg = combineUsages rhs_usgs
; (_, specs) <- specLoop rhs_env2 force_spec
(scu_calls rhs_usg) rhs_infos nullUsage
[SI [] 0 Nothing | _ <- bndrs]
; return (rhs_env1,
Rec (concat (zipWith specInfoBinds rhs_infos specs))) }
where
(bndrs,rhss) = unzip prs
force_spec = any (forceSpecBndr env) bndrs
scTopBind env (NonRec bndr rhs)
= do { (_, rhs') <- scExpr env rhs
; let (env1, bndr') = extendBndr env bndr
env2 = extendValEnv env1 bndr' (isValue (sc_vals env) rhs')
; return (env2, NonRec bndr' rhs') }
scRecRhs :: ScEnv -> (OutId, InExpr) -> UniqSM (ScUsage, RhsInfo)
scRecRhs env (bndr,rhs)
= do { let (arg_bndrs,body) = collectBinders rhs
(body_env, arg_bndrs') = extendBndrsWith RecArg env arg_bndrs
; (body_usg, body') <- scExpr body_env body
; let (rhs_usg, arg_occs) = lookupOccs body_usg arg_bndrs'
; return (rhs_usg, RI bndr (mkLams arg_bndrs' body')
arg_bndrs body arg_occs) }
specInfoBinds :: RhsInfo -> SpecInfo -> [(Id,CoreExpr)]
specInfoBinds (RI fn new_rhs _ _ _) (SI specs _ _)
= [(id,rhs) | OS _ _ id rhs <- specs] ++
[(fn `addIdSpecialisations` rules, new_rhs)]
where
rules = [r | OS _ r _ _ <- specs]
varUsage :: ScEnv -> OutVar -> ArgOcc -> ScUsage
varUsage env v use
| Just RecArg <- lookupHowBound env v = SCU { scu_calls = emptyVarEnv
, scu_occs = unitVarEnv v use }
| otherwise = nullUsage
\end{code}
%************************************************************************
%* *
The specialiser itself
%* *
%************************************************************************
\begin{code}
data RhsInfo = RI OutId
OutExpr
[InVar] InExpr
[ArgOcc]
data SpecInfo = SI [OneSpec]
Int
(Maybe ScUsage)
data OneSpec = OS CallPat
CoreRule
OutId OutExpr
specLoop :: ScEnv
-> Bool
-> CallEnv
-> [RhsInfo]
-> ScUsage -> [SpecInfo]
-> UniqSM (ScUsage, [SpecInfo])
specLoop env force_spec all_calls rhs_infos usg_so_far specs_so_far
= do { specs_w_usg <- zipWithM (specialise env force_spec all_calls) rhs_infos specs_so_far
; let (new_usg_s, all_specs) = unzip specs_w_usg
new_usg = combineUsages new_usg_s
new_calls = scu_calls new_usg
all_usg = usg_so_far `combineUsage` new_usg
; if isEmptyVarEnv new_calls then
return (all_usg, all_specs)
else
specLoop env force_spec new_calls rhs_infos all_usg all_specs }
specialise
:: ScEnv
-> Bool
-> CallEnv
-> RhsInfo
-> SpecInfo
-> UniqSM (ScUsage, SpecInfo)
specialise env force_spec bind_calls (RI fn _ arg_bndrs body arg_occs)
spec_info@(SI specs spec_count mb_unspec)
| not (isBottomingId fn)
, not (isNeverActive (idInlineActivation fn))
, notNull arg_bndrs
, Just all_calls <- lookupVarEnv bind_calls fn
= do { (boring_call, pats) <- callsToPats env specs arg_occs all_calls
; let n_pats = length pats
spec_count' = n_pats + spec_count
; case sc_count env of
Just max | not force_spec && spec_count' > max
-> pprTrace "SpecConstr" msg $
return (nullUsage, spec_info)
where
msg = vcat [ sep [ ptext (sLit "Function") <+> quotes (ppr fn)
, nest 2 (ptext (sLit "has") <+>
speakNOf spec_count' (ptext (sLit "call pattern")) <> comma <+>
ptext (sLit "but the limit is") <+> int max) ]
, ptext (sLit "Use -fspec-constr-count=n to set the bound")
, extra ]
extra | not opt_PprStyle_Debug = ptext (sLit "Use -dppr-debug to see specialisations")
| otherwise = ptext (sLit "Specialisations:") <+> ppr (pats ++ [p | OS p _ _ _ <- specs])
_normal_case -> do {
let spec_env = decreaseSpecCount env n_pats
; (spec_usgs, new_specs) <- mapAndUnzipM (spec_one spec_env fn arg_bndrs body)
(pats `zip` [spec_count..])
; let spec_usg = combineUsages spec_usgs
(new_usg, mb_unspec')
= case mb_unspec of
Just rhs_usg | boring_call -> (spec_usg `combineUsage` rhs_usg, Nothing)
_ -> (spec_usg, mb_unspec)
; return (new_usg, SI (new_specs ++ specs) spec_count' mb_unspec') } }
| otherwise
= return (nullUsage, spec_info)
spec_one :: ScEnv
-> OutId
-> [InVar]
-> InExpr
-> (CallPat, Int)
-> UniqSM (ScUsage, OneSpec)
spec_one env fn arg_bndrs body (call_pat@(qvars, pats), rule_number)
= do { spec_uniq <- getUniqueUs
; let spec_env = extendScSubstList (extendScInScope env qvars)
(arg_bndrs `zip` pats)
fn_name = idName fn
fn_loc = nameSrcSpan fn_name
spec_occ = mkSpecOcc (nameOccName fn_name)
rule_name = mkFastString ("SC:" ++ showSDoc (ppr fn <> int rule_number))
spec_name = mkInternalName spec_uniq spec_occ fn_loc
; (spec_usg, spec_body) <- scExpr spec_env body
; let spec_id = mkLocalId spec_name (mkPiTypes spec_lam_args body_ty)
`setIdStrictness` spec_str
`setIdArity` count isId spec_lam_args
spec_str = calcSpecStrictness fn spec_lam_args pats
(spec_lam_args, spec_call_args) = mkWorkerArgs qvars body_ty
spec_rhs = mkLams spec_lam_args spec_body
body_ty = exprType spec_body
rule_rhs = mkVarApps (Var spec_id) spec_call_args
inline_act = idInlineActivation fn
rule = mkRule True True
rule_name inline_act fn_name qvars pats rule_rhs
; return (spec_usg, OS call_pat rule spec_id spec_rhs) }
calcSpecStrictness :: Id
-> [Var] -> [CoreExpr]
-> StrictSig
calcSpecStrictness fn qvars pats
= StrictSig (mkTopDmdType spec_dmds TopRes)
where
spec_dmds = [ lookupVarEnv dmd_env qv `orElse` lazyDmd | qv <- qvars, isId qv ]
StrictSig (DmdType _ dmds _) = idStrictness fn
dmd_env = go emptyVarEnv dmds pats
go env ds (Type {} : pats) = go env ds pats
go env (d:ds) (pat : pats) = go (go_one env d pat) ds pats
go env _ _ = env
go_one env d (Var v) = extendVarEnv_C both env v d
go_one env (Box d) e = go_one env d e
go_one env (Eval (Prod ds)) e
| (Var _, args) <- collectArgs e = go env ds args
go_one env _ _ = env
\end{code}
Note [Specialise original body]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The RhsInfo for a binding keeps the *original* body of the binding. We
must specialise that, *not* the result of applying specExpr to the RHS
(which is also kept in RhsInfo). Otherwise we end up specialising a
specialised RHS, and that can lead directly to exponential behaviour.
Note [Transfer activation]
~~~~~~~~~~~~~~~~~~~~~~~~~~
This note is for SpecConstr, but exactly the same thing
happens in the overloading specialiser; see
Note [Auto-specialisation and RULES] in Specialise.
In which phase should the specialise-constructor rules be active?
Originally I made them always-active, but Manuel found that this
defeated some clever user-written rules. Then I made them active only
in Phase 0; after all, currently, the specConstr transformation is
only run after the simplifier has reached Phase 0, but that meant
that specialisations didn't fire inside wrappers; see test
simplCore/should_compile/spec-inline.
So now I just use the inline-activation of the parent Id, as the
activation for the specialiation RULE, just like the main specialiser;
This in turn means there is no point in specialising NOINLINE things,
so we test for that.
Note [Transfer strictness]
~~~~~~~~~~~~~~~~~~~~~~~~~~
We must transfer strictness information from the original function to
the specialised one. Suppose, for example
f has strictness SS
and a RULE f (a:as) b = f_spec a as b
Now we want f_spec to have strictess LLS, otherwise we'll use call-by-need
when calling f_spec instead of call-by-value. And that can result in
unbounded worsening in space (cf the classic foldl vs foldl')
See Trac #3437 for a good example.
The function calcSpecStrictness performs the calculation.
%************************************************************************
%* *
\subsection{Argument analysis}
%* *
%************************************************************************
This code deals with analysing call-site arguments to see whether
they are constructor applications.
\begin{code}
type CallPat = ([Var], [CoreExpr])
callsToPats :: ScEnv -> [OneSpec] -> [ArgOcc] -> [Call] -> UniqSM (Bool, [CallPat])
callsToPats env done_specs bndr_occs calls
= do { mb_pats <- mapM (callToPats env bndr_occs) calls
; let good_pats :: [([Var], [CoreArg])]
good_pats = catMaybes mb_pats
done_pats = [p | OS p _ _ _ <- done_specs]
is_done p = any (samePat p) done_pats
; return (any isNothing mb_pats,
filterOut is_done (nubBy samePat good_pats)) }
callToPats :: ScEnv -> [ArgOcc] -> Call -> UniqSM (Maybe CallPat)
callToPats env bndr_occs (con_env, args)
| length args < length bndr_occs
= return Nothing
| otherwise
= do { let in_scope = substInScope (sc_subst env)
; prs <- argsToPats env in_scope con_env (args `zip` bndr_occs)
; let (interesting_s, pats) = unzip prs
pat_fvs = varSetElems (exprsFreeVars pats)
qvars = filterOut (`elemInScopeSet` in_scope) pat_fvs
(tvs, ids) = partition isTyCoVar qvars
qvars' = tvs ++ ids
;
if or interesting_s
then return (Just (qvars', pats))
else return Nothing }
argToPat :: ScEnv
-> InScopeSet
-> ValueEnv
-> CoreArg
-> ArgOcc
-> UniqSM (Bool, CoreArg)
argToPat _env _in_scope _val_env arg@(Type {}) _arg_occ
= return (False, arg)
argToPat env in_scope val_env (Note _ arg) arg_occ
= argToPat env in_scope val_env arg arg_occ
argToPat env in_scope val_env (Let _ arg) arg_occ
= argToPat env in_scope val_env arg arg_occ
argToPat env in_scope val_env (Cast arg co) arg_occ
| not (ignoreType env ty2)
= do { (interesting, arg') <- argToPat env in_scope val_env arg arg_occ
; if not interesting then
wildCardPat ty2
else do
{
uniq <- getUniqueUs
; let co_name = mkSysTvName uniq (fsLit "sg")
co_var = mkCoVar co_name (mkCoKind ty1 ty2)
; return (interesting, Cast arg' (mkTyVarTy co_var)) } }
where
(ty1, ty2) = coercionKind co
argToPat env in_scope val_env arg arg_occ
| Just (ConVal dc args) <- isValue val_env arg
, not (ignoreAltCon env dc)
, case arg_occ of
ScrutOcc _ -> True
BothOcc -> case arg of
App {} -> True
_other -> False
_other -> False
= do { args' <- argsToPats env in_scope val_env (args `zip` conArgOccs arg_occ dc)
; return (True, mk_con_app dc (map snd args')) }
argToPat env in_scope val_env (Var v) arg_occ
| case arg_occ of { UnkOcc -> False; _other -> True },
is_value,
not (ignoreType env (varType v))
= return (True, Var v)
where
is_value
| isLocalId v = v `elemInScopeSet` in_scope
&& isJust (lookupVarEnv val_env v)
| otherwise = isValueUnfolding (idUnfolding v)
argToPat _env _in_scope _val_env arg _arg_occ
= wildCardPat (exprType arg)
wildCardPat :: Type -> UniqSM (Bool, CoreArg)
wildCardPat ty = do { uniq <- getUniqueUs
; let id = mkSysLocal (fsLit "sc") uniq ty
; return (False, Var id) }
argsToPats :: ScEnv -> InScopeSet -> ValueEnv
-> [(CoreArg, ArgOcc)]
-> UniqSM [(Bool, CoreArg)]
argsToPats env in_scope val_env args
= mapM do_one args
where
do_one (arg,occ) = argToPat env in_scope val_env arg occ
\end{code}
\begin{code}
isValue :: ValueEnv -> CoreExpr -> Maybe Value
isValue _env (Lit lit)
= Just (ConVal (LitAlt lit) [])
isValue env (Var v)
| Just stuff <- lookupVarEnv env v
= Just stuff
| not (isLocalId v) && isCheapUnfolding unf
= isValue env (unfoldingTemplate unf)
where
unf = idUnfolding v
isValue env (Lam b e)
| isTyCoVar b = case isValue env e of
Just _ -> Just LambdaVal
Nothing -> Nothing
| otherwise = Just LambdaVal
isValue _env expr
| (Var fun, args) <- collectArgs expr
= case isDataConWorkId_maybe fun of
Just con | args `lengthAtLeast` dataConRepArity con
-> Just (ConVal (DataAlt con) args)
_other | valArgCount args < idArity fun
-> Just LambdaVal
_other -> Nothing
isValue _env _expr = Nothing
mk_con_app :: AltCon -> [CoreArg] -> CoreExpr
mk_con_app (LitAlt lit) [] = Lit lit
mk_con_app (DataAlt con) args = mkConApp con args
mk_con_app _other _args = panic "SpecConstr.mk_con_app"
samePat :: CallPat -> CallPat -> Bool
samePat (vs1, as1) (vs2, as2)
= all2 same as1 as2
where
same (Var v1) (Var v2)
| v1 `elem` vs1 = v2 `elem` vs2
| v2 `elem` vs2 = False
| otherwise = v1 == v2
same (Lit l1) (Lit l2) = l1==l2
same (App f1 a1) (App f2 a2) = same f1 f2 && same a1 a2
same (Type {}) (Type {}) = True
same (Note _ e1) e2 = same e1 e2
same (Cast e1 _) e2 = same e1 e2
same e1 (Note _ e2) = same e1 e2
same e1 (Cast e2 _) = same e1 e2
same e1 e2 = WARN( bad e1 || bad e2, ppr e1 $$ ppr e2)
False
bad (Case {}) = True
bad (Let {}) = True
bad (Lam {}) = True
bad _other = False
\end{code}
Note [Ignore type differences]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We do not want to generate specialisations where the call patterns
differ only in their type arguments! Not only is it utterly useless,
but it also means that (with polymorphic recursion) we can generate
an infinite number of specialisations. Example is Data.Sequence.adjustTree,
I think.