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1 point by binx 4123 days ago | link | parent

Things that have to be remembered:

1. Local functions which have enclosing environments are harder to inline. If a function's environment is different to the caller's environment, we should replace all its free variables to references to its environment. For simplicity, you can inline only the combinators(functions which have no free variables).

2. When inlining, we should rewrite the parameters only if they are free to the function body, not bound by other local functions in the body.



1 point by almkglor 4123 days ago | link

1. I'm not proposing yet to inline local functions, especially those that close on environments. However, what algorithm would you propose for inlining local functions?

As an aside, closure-conversion makes the creation of environments explicit. Perhaps an inlining step can be added after closure-conversion?

2. I don't understand this part.

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3 points by binx 4123 days ago | link

2. Take this function as an example:

(fn (x y) (g x y (fn (x) (h x))))

When inlined with x=1 and y=2, it should be rewritten as:

(g 1 2 (fn (x) (h x))), not

(g 1 2 (fn (x) (h 1)))

Because the second x is not free in the function body.

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2 points by almkglor 4123 days ago | link

I see. This is actually handled implicitly in the compiler's AST structure: during the conversion from the list form to the AST form, each local variable is given a unique ID:

  (fn (x y) (g x y (fn (x) (h x))))
  =>
  (fn (x@1 y@2) (g x@1 y@2 (fn (x@3) (h x@3))))
  ; approximation of the AST structure, the AST
  ; is really a table of properties
So mindless replacement of the inlined version will simply replace x@1, not x@3.

  (g 1 2 (fn (x@3) (h x@3)))

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1 point by almkglor 4122 days ago | link

Hmm. Turns out this is a real issue, but for a different reason: since local variables are given unique ID's, we should actually replace local variable ID's for subfunctions when a function is inlined several times:

  (set glob
    (fn (x@1 y@2)
      (g x@1 y@2 (fn (x@3) (h x@3))))
  (glob 1 2)
  (glob 3 4)
  =>
  (set glob
    (fn (x@1 y@2)
      (g x@1 y@2 (fn (x@3) (h x@3))))
  (g 1 2
    (fn (x@4) (h x@4)))
  (g 3 4
    (fn (x@5) (h x@5)))

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