define-inline does not respect inline-limit

[johnwcowan]

If you define a recursive procedure with define-inline, csc 4.8.0.4 loops.

(define-inline (foo x) (if (= x 0) 0 (+ (foo (- x 1)) 1)))
(foo 32)

Compile with csc -t, wait forever. This is not the case with

(declare (inline foo))
(define (foo x) (if (= x 0) 0 (+ (foo (- x 1)) 1)))
(foo 32)

which suppresses the inlining.

[sjamaan]

A bit silly, but if we can easily fix it, that should probably go into 4.10.0

[evhan]

The define-inline feature is pretty much totally distinct from procedure inlining (to which (declare (inline ...)) and inline-limit apply) -- the former is strictly mechanical and takes place during canonicalization, whereas the latter happens later on when the optimizer decides whether or not to inline a predefined procedure or not. Also, inline-limit is a threshold of procedure size, which can't be easily applied to define-inline forms.

To prevent loops, we could add a depth limit for nested define-inline expansions. Or, this may just be a documentation bug that we fix by making clear that define-inline is a naive transformation and if you're not careful, recursive inlines may loop forever. I'd prefer the latter.

Thoughts?

[evhan]

I've added a note to define-inline's documentation that inline-limit doesn't apply to it in 5d102c31cef490e6e3d3bd8f0044801ed4e50d0e.

A cutoff for nested define-inline expansion should really be a separate feature request, as described above. For now, I'm going to call this a documentation bug and mark it resolved. Please open a new enhancement request if such a feature would be valuable to you.