Re: multi-language to JVM compilers?

["W. Wesley Groleau x4923" <wwgrol@pseserv3.fw.hac.com>]

> Java, and various Java tools would be useless, since the semantic
> level of the JVM generated would be completely wrong. OK, you know
> the JVM specs, but perhaps you do not have a clear idea of the 
> semantic level of a GCC backend, which is a very simple machine model 
> with a limited number of registers.

The JVM and p-code models were very simple in most respects and had 
a limited number of registers.  Where they got complex was in the
frame-handling/subprogram calling instructions where the object code
format/class format was entangled with the instructions that performed
a procedure call/class loading.  (as I recall....)

> By contrast generating silly JVM output from the backend of GCC is by
> contrast trivial, and probably no more than a few weeks work. The fact
> that you think it is a bigger task must mean you have some major
> misconceptions, I can't quite guess what.

The "fact that I think it is a bigger task" is more accurately the 
fact that other people have claimed it is a bigger task.  First,
there were Usenet posts that said starting from the AST was
more feasible (which I may have misinterpreted as meaning easier)
because the byte code was at a higher level that was more similar to
the semantic level of the tree.  Then there was S. Tucker Taft's
paper explaining how Ada features and Java features were so 
straightforwardly mapped onto each other.  

Now you say that a byte-code generating back-end is trivial but 
mapping to the intermediate form is difficult, and that I am 
confused to think otherwise.  I'm not accusing anyone of changing
his/her tune, but I certainly haven't changed mine!

I also do not agree with the apparent suggestion that we can make
object files derived from several different languages compatible
with each other and and with symbolic debuggers, but we can't make
JVM byte-code class files from more than one language "interface
with Java, and the various Java tools."

But my main point is that being able to generate Java classes
from several different languages _would_ be a Good Thing, whether
difficult or not.  That is not to say I fault anyone from doing
whatever he/she/they believes his/her/their customers want/need.

-- 
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    Wes Groleau, Hughes Defense Communications, Fort Wayne, IN USA
Senior Software Engineer - AFATDS                  Tool-smith Wanna-be
                    wwgrol AT pseserv3.fw.hac.com

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