[armedbear-devel] Progress on generic-class-file branch

Erik Huelsmann ehuels at gmail.com
Sun Aug 1 12:45:28 UTC 2010

Today, updated tests were committed to the branch which allow it to
generate ABCL function classes, load them and execute them. That's
exciting news! It basically means that the branch is good enough for
anybody to write their own lisp code to create new classes (whether or
not they are ABCL functions doesn't really matter).

So, where does that leave us in the bigger picture? Well, even though
it's now possible to generate function classes with your own lisp
code, the generator hasn't been fully integrated into the compiler.
The bit that I did integrate is the use of the CLASS-NAME structure
for identification of classes and class references. Next to that, I
adjusted the method invoking emitters to use different pool functions
for creation of the method refs.

So, what remains to be done?

 * A test needs to be created which tests nested use of
WITH-CODE-TO-METHOD, making sure that
   register allocation in the nested function generator is correctly
transferred to the outer block (more on that below)
 * The pool handling needs to be switched over to the new pool functions
    Possibly, there's a quick-path here by changing the pool-*
functions in p2 to forward to the ones in j-c-f (jvm-class-file).
 * The exception handler creation needs to be adjusted to use the new
 * Changing the compiler away from *code* and *static-code* toward
 * Clean up: removal of unused functions (after integration)
[especially those currently conflicting]
 * Documentation: Not all functions in the j-c-f file are documented.
   All functions except the internal ones (starting with %) should be
 * API declaration
   None of the functions in the file are currently exported  or
autoloaded (unless by accident). In order to
   help others to create their own classes, we should probably export
(some) of the functions, for runtime-class
   to build upon.

It'd be my preference to do the integration work on the branch, unless
we find a strategy to keep trunk stable while we change its class file
generator - one of the most critical components.

When all the above has been completed, I see the following
improvements to be made to the code we generate:

 * multiple methods to handle &optional processing, instead of
fastProcessArgs, if the method has less than 8
   parameters in total
 * moving initialization of static variables to a static {} block,
instead of in the (re-runnable) constructor;
   besides being a nice improvement, this is actually a correctness
issue: our current constructors call
   Lisp.recall(), which can't be called more than once for a given string value
 * Reduction of the number of function classes generated: non-inlined
local functions generated as methods in
   the function class
 * Re-introduction of XEPs (External entry points): SBCL uses a
paradigm where functions which are hard-linked
   together, use internal entry points: they flatten keywords, pass
the right ([un]boxed) values, etc, skipping the
   "parameter discovery" checks. XEPs discover the right parameters
and call the internal entry point.

Apart from that, we should (finally) be able to implement
runtime-class without depending on ASM.

Now, there's the explanation of what should be tested in the test-to-be-written:

WITH-CODE-TO-METHOD catches the output from EMIT. Sometimes, pass2
wants to output a small block of code to the constructor method while
in the midst of writing an "execute" method. Even fewer times, but in
general  quite thinkable, you could see the following nesting with
output to two methods, method1 and method2:

 (WITH-CODE-TO-METHOD (file method1)
   (WITH-CODE-TO-METHOD (file method2)
      (WITH-CODE-TO-METHOD (file method1)

The WITH-CODE-TO-METHOD macro provisions for this scenario by saving
the values of the compiler-specials to the Code attribute. However,
currently, nothing checks if the code works correctly (ie saves enough
specials). The test should establish that.

Ok. Sorry for the lengthy e-mail :-)



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