[Mono-list] Reference runtime internal variable in managed code

[Paolo Molaro]

On 08/26/03 Derek Woo wrote:
> Sorry for being unclear. I am working in the context of adaptive
> optimization. Maybe I would use a small example:
> 
> Method mthA {
>     
>      // Call some method B here
> }
> 
> What I want to do is have the JIT patch the code of mthA as it is compiling
> it such that it becomes:
> 
> Method mthA {
>     
>      if (condition) {
>          // Call some method C
>      }
>      else {
>          // Call some method B here
>      }
> }

Wouldn't it make more sense to just change method C to read:

	if (condition) {
		call method B;
		return;
	}
	... normal method C code ...

This way you keep code expansion low and it's easier to implement in the
JIT, since it's just stuff you can do in the prolog, for example.

> Now there are some requirement:
> 1. "condition" is a reference to internal data of the runtime, e.g. the
> execution count of a method, or some info that is collected from the
> profiler.
> 2. The condition check is done as "mthA" is actually executing.
> 
> Basically, the runtime passed a reference of some data, to a piece of user
> code. And the user code checked that data for some condition.
> 
> I can certainly do the patching in "mono_method_to_ir()". But the problem is
> how I can enable such condition check from user code to internal data
> structure of the runtime. And do it quickly.


You can do it in three ways:
*) in mono_method_to_ir () by generating the intermediate code directly
(this also means it will be portable). This is the reccomended way.
*) you can do it in mini-x86.c in emit_prolog: hackish non portable way.
*) you can do it using wrappers, like it's done for some methods in
metadata/marshal.c. It's portable, but you need to generate IL code and
it's more cumbersome and runtime-heavy.

I suggest the first way to do it. You may want to grep for coverage_info
in mini.c to see how a static unmanaged variable is accessed in the
internal representation. There are plenty of examples there on how to
call a method as well.

lupus

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