Re: types and generic function performance

Hi Bob,

> Hello and thanks for writing Bigloo!
> 
> I have a question about performance ... I wrote this program:
> 
> ;------------------------
> (module test
>         (main scm-main)
>         (export
>         (class TestClass)
>         ))
> 
> (define-generic (test-func obj) (print "GENERIC METHOD"))
> (define-method (test-func obj::TestClass) (print "TEST METHOD"))
> 
> (define (scm-main argv)
>   (let ((tc::TestClass (instantiate::TestClass)))
>     (test-func tc)))
> 
> ;------------------------
> 
> Which works as expected, producing the output "TEST METHOD", but if I look at the generated C code it looks like it is calling test-func dynamically even though I have specified the class type with tc::TestClass.
> 
>  
> 
> Is there some way to make such generic functions faster by calling the correct define-method function directly if the type is known?
> 
> Thanks,
You are correct in your observation. The compiler does not implement
this optimization. I have never conducted any experiment to check if
it would frequently apply in practice.

As it is, the calling a method instead of a regular function incurs a
couple of memory read + a indirect call. Your function TEST-FUNC is compiled
as follows:

(define-generic (test-func obj)
  (let ((test1086 (object? obj)))
    (if test1086
      (let ((method1053
              (unsafe (find-method obj (closure test-func)))))
        (funcall method1053 method1053 obj))
      (let ((fun1087 (generic-default (closure test-func))))
        (funcall fun1087 fun1087 obj)))))

and FIND-METHOD is defined by:

(define-inline (find-method obj generic)
   (let ((obj-class-num (object-class-num obj)))
      (method-array-ref generic (generic-method-array generic) obj-class-num)))


You can check this with bigloo -unsafe -O2 -fno-user-inlining -ast

Cheers,

-- 
Manuel