)
import OccName ( EncodedFS, mkWorkerOcc )
import PrimRep ( PrimRep )
-import TysPrim ( statePrimTyCon )
import FieldLabel ( FieldLabel )
import Maybes ( orElse )
import SrcLoc ( SrcLoc )
idLBVarInfo id = lbvarInfo (idInfo id)
isOneShotLambda :: Id -> Bool
-isOneShotLambda id = analysis || hack
+isOneShotLambda id = analysis
where analysis = case idLBVarInfo id of
LBVarInfo u | u `eqUsage` usOnce -> True
other -> False
- hack = case splitTyConApp_maybe (idType id) of
- Just (tycon,_) | tycon == statePrimTyCon -> True
- other -> False
-
- -- The last clause is a gross hack. It claims that
- -- every function over realWorldStatePrimTy is a one-shot
- -- function. This is pretty true in practice, and makes a big
- -- difference. For example, consider
- -- a `thenST` \ r -> ...E...
- -- The early full laziness pass, if it doesn't know that r is one-shot
- -- will pull out E (let's say it doesn't mention r) to give
- -- let lvl = E in a `thenST` \ r -> ...lvl...
- -- When `thenST` gets inlined, we end up with
- -- let lvl = E in \s -> case a s of (r, s') -> ...lvl...
- -- and we don't re-inline E.
- --
- -- It would be better to spot that r was one-shot to start with, but
- -- I don't want to rely on that.
- --
- -- Another good example is in fill_in in PrelPack.lhs. We should be able to
- -- spot that fill_in has arity 2 (and when Keith is done, we will) but we can't yet.
setOneShotLambda :: Id -> Id
setOneShotLambda id = modifyIdInfo (`setLBVarInfo` LBVarInfo usOnce) id