Re: [xmlvm-users] pop2

[Arno P. <ar...@pu...>]

On 12/16/09 4:19 PM, Gergely Kis wrote:
> Actually XMLVM already makes a distinction in the code between the
> different types, because you generate the following code:
> _st[_sp++].i  - for integers
> _st[_sp++].d - for double
> ... etc.
> The only problem is that in C, you cannot inspect at runtime what is
> stored in a union.
> One idea would be to make a small change in XMLVMElem to also allow the
> storage of the type that was stored in it, and change the generated code
> to something like this:
>
> _st[_sp++].type = 'i'; _st[_sp].i = ...;

The JVM usually only allocated 32-bits per stack element to save space. 
sizeof(XMLVMElem) is 64 bits, that is the core of the problem. Keeping 
type information at runtime or doing an offline data flow analysis would 
be solutions to this problem. However, both are pretty complex and since 
we plan to switch to a register-based machine in the near, mid-term 
future it would be unnecessary work. As I pointed out in my previous 
post, there is an easy way to avoid the pop2 instruction.

> Do you have more information regarding the register machine conversion
> that you are doing? Do you have a timeframe? Will it change the
> interface between the hand-written objc code and the generated code?
> Do you use the DEX model which I mentioned earlier, or are you inventing
> something else?

We make use of the DEX compiler. As a matter of fact, you can already 
see dx.jar in our repository and a DEX output process. Sascha is working 
on this so I let him talk about timeframe.  :-)

The very important fact is that the name-mangling *will not* change, so 
the hand-written code will not need to be changed.

Arno