[llvm-commits] [patch] CodeEmitter Memory Foot Reduction

[Bruno Cardoso Lopes]

On Thu, Jul 16, 2009 at 3:27 AM, Chris Lattner<clattner at apple.com> wrote:
> On Jul 15, 2009, at 9:01 AM, Aaron Gray wrote:
>>
>> Chris,
>>
>> If you/we do not like this code, then the alternatives are :-
>> 1) Leave as is, which I would not suggest.
>> 2) Revert to using MachineCodeEmitter like mechanics with virtual extend()
>> method to allow rebuffering with ObjectCodeEmitter providing the memory
>> management.
>> 3) Don't really know of any other alternatives :)
>>
>> 2 maybe the best compromise option. Its easy to code, removes templating
>> from the CodeEmitters, and is virtually transparent to our other DOE work.
>> The only thing it does not write via a BinaryObject object, so we loose that
>> functionality.
>
> Hi Aaron,
>
> I'm sorry for not getting back to you sooner.  I work fairly LIFO and the
> craziness that has happened since your emails have distracted me.
>
> One problem with this patch is that (for example) X86TargetMachine.cpp
> refers to the "createX86ObjectCodeEmitterPass" symbol, which forces the code
> emitter to object code emitter to be linked into the X86 target module.
>  There is still no way to create a JIT without two copies of the code
> emitter template.  I believe that aligning this work with Daniels work to
> make the targets more modular would be straight forward.  Are you willing to
> do this?
>
> This patch keeps around the templates, which I really don't like.  However,
> this is better than what is in mainline, so it seems like a reasonable step
> to me if you really really want to do this.  However, I still don't
> understand why you're unwilling to make the CodeEmitter be a virtual base
> class instead of a template!

In addition to what Chris said, we could also make MachineCodeEmitter
a class with only pure
virtual functions and move everything related to BufferBegin,
BufferEnd and CurBufferPtr to
JITCodeEmitter. This way we can use MCE as a base class for OCE, JCE
and don't lose
BinaryObject functionality.

-- 
Bruno Cardoso Lopes
http://www.brunocardoso.cc