Re: sparse: Why test-parse shows "+=" as a store?

[Jeff Garzik <jeff@garzik.org>]

Christopher Li wrote:
> On Mon, Apr 27, 2009 at 3:28 AM, Jeff Garzik <jeff@garzik.org> wrote:
>> Use of test-parsing eliminates my code as a factor -- which was why I
>> mentioned it.
>>
>> Oh well, I will figure it out.
> 
> Let me take a look at your code as well. Maybe I can spot some thing.
> 
>> linearized output is too low level for LLVM in several cases.  The shifts in
>> linearize_load_gen() and linearize_store_gen() get in the way, for example.
>>  Having sparse calculate struct offsets itself is also not desirable: in
>> order to use LLVM's getelementptr instruction, you should instead give LLVM
>> the type information and member indices, and let it figure out the address
>> calculation from there.
> 
> Right. I think GET_ELEMENT_PTR is the only part missing. I think it is
> a relative small change to preserve the structure laid, comparing to rewriting
> everything.
> 
> BTW, I don't think linearize lost that structure information. It
> happens way before
> linearize stage. Sparse converts the structure member access into void pointer
> add very early on. If you want to preserve that information,
> you need to change more than just linearize code. So linearize is not the
> blocking factor here. It needs upstream change as well.

I just managed to figure out how to locate, enumerate and declare sparse 
SYM_STRUCT to LLVM backend, in s2l-gen.c, without any upstream changes.


>> Thus, use of linearize would imply having to work backwards and recreate
>> information lost during the linearization.
> 
> Or, we can teach sparse to preserve that information in the linearize level.

Well, I'll tell you what.  If you or somebody else wants to volunteer to 
make key sparse & linearize changes, then I will work on a linearize 
LLVM backend.

Absent that, the motivation is lower, considering I have a current, 
working approach that does not require any upstream changes.

	Jeff