[LLVMdev] [patch] CodeEmitter Memory Foot Reduction

Daniel Dunbar daniel at zuster.org
Thu Jul 16 11:03:10 PDT 2009

On Thu, Jul 16, 2009 at 10:04 AM, Aaron
Gray<aaronngray.lists at googlemail.com> wrote:
> 2009/7/16 Chris Lattner <clattner at apple.com>
>> Whats Daniels approach, does he have any online documentation or code, do
>> you have an email address so I may talk to him.
>> Take a look at how asmprinters work
>> in include/llvm/Target/TargetRegistry.h .  If you have specific questions,
>> llvmdev is a great place to ask them.
> Okay I will take a look.

I don't have any documentation yet other than the doxygen comments
(some will be added at least before 2.6), but the basic idea is that
there is one global Target instance per target, and targets register
optional components via initialization functions (which can be called
via static constructors, or explicitly by the client).

Clients of the targets simple request a Target, which will always be
linked in, and look to see if the optional functionality is present
(i.e. was linked in).

 - Daniel

> Aaron
>> -Chris
>> Aaron
>> 2009/7/16 Chris Lattner <clattner at apple.com>
>>> 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!
>>> -Chris
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