Version 5 (modified by kirsten, 10 years ago) (diff) |
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# Linearity

Instead of:

type DmdEnv = VarEnv Demand

we want:

type DmdEnv = Env CoreExpr Demand

We keep track of demands on partial applications.

After calling dmd_anal on the body of a let, which results in demand type `dmd_ty` with demand env `dmd_env`, we do the following for each let-bound variable `f`:

- Iterate through all the keys in
`dmd_env`, finding all applications of`f`to*n*arguments. - For each
*i*from 1 through*n*(where*n*is`f`'s arity), if each of the applications of`f`to*i*arguments has usage demand`OneOrZero`, then it's safe to mark the corresponding lambda-expression as a one-shot lambda.

This might work, but is kind of kludgy.

This may be *way* too unnecessarily complicated. Can't we just get the same information from the demand on f in the free-var environment of the let body as it is, without changing the environment?

suppose the demand on f is

S1K(S1K(LMX))

if f =

(\ x. (\ y. ...))

then we can mark the outer two lambdas as being one-shot. Right?

Not exactly. Suppose:

let f = \ x. \ y. ... in ...(f 1 2)...(f 3 4)...

f will have demand on it:

SMK(SMK(LMX))

because it's called more than once. (But maybe that's okay? If it instead were:

let f = \ x. \ y. ... in ...(f 1)...(f 3 4)...

then the demand would be:

SMK(LMX)

and we would know that there was a partial application? Getting confused here.)