[LLVMdev] tblgen internals

[Garrison Venn]

Concerning the RecordKeeper reference in Record. Would you prefer to partially go
back to a more limited constrained version of a global. Since we are not threaded anyway,
we could turn the reference into a singleton for the duration of an initial parse and use session.
The concept would be to instead make the reference a static pointer, make RecordKeeper
a friend of Record, and add RecordKeeper::resetSession(void). resetSession would set
the static pointer to itself. Asserts would also have to be added to the methods which needed
a Record to have a non-NULL RecordKeeper pointer. Although we would in effect still be
using a global, we would be allowing it to be controlled while simultaneously removing the
sizeof(RecordKeeper*) number of bytes from Record instances. Offsets into a another say 
SmallVector instance could also be attempted, but this seems messy to me. 

I am of course assuming that your use of the word suboptimal was concerned with the added
size to Record.

Anyway just a thought

Garrison

On Dec 12, 2010, at 21:52, Garrison Venn wrote:

> Hi Chris,
> 
> Thanks for the review!
> 
> I believe I caught most of the syntax style issues with the attached patch. It only contains
> these style changes.
> 
> On Dec 12, 2010, at 19:30, Chris Lattner wrote:
> 
>> 
>> On Dec 12, 2010, at 10:54 AM, Garrison Venn wrote:
>> 
>>> 
>>> Hey Chris,
>>> 
>>> The following patch removes all global references to a RecordKeeper instance for the tblgen
>>> utility. 
>> 
>> This looks like great progress to me, applied in r121659.
>> 
>> That said, it is suboptimal for Record to have to have a RecordKeeper& in it.  I haven't looked at the code in a long time, is it feasible to detangle that out of record, or is it not worth it?
> 
> I'll see if I can come up with another approach. This internal reference was motivated by the
> Record::setName(...) and UnOpInit::Fold(...) implementations accessing the previous 
> global RecordKeeper instance. We could add a RecordKeeper& argument to setName
> and OpInit::Fold(...). However as I'm looking at the code, while adding this argument to Fold
> for TGParser use is not an issue as it has a RecordKeeper instance, the other Record
> classes have a problem because they lack this type of instance. See for example the
> implementation of Record.cpp:OpInit::resolveBitReference(...). These methods (such as
> resolveBitReference(...) and resolveReferences(...) need a context containing a RecordKeeper
> for their evaluation. A cursory glance for the uses of Record::setName(...) seems to imply that adding a 
> RecordKeeper& argument would not be an issue. I'll keep on looking for other mechanisms.
> 
>> 
>> Another random question: why is createRecord better than using "new Record"?  If createRecord is better, it would be good to make the Record ctor private so the code doesn't evolve into sometimes using one and sometimes using the other.
> 
> This was another syntactic hack. I personally prefer the factory approach, but I cannot
> as it stands get rid of the explicit Record constructor because of MultiClass. It has member
> variable of type Record and constructs this member directly using the Record constructor.
> It therefore does not need the allocation provided by createRecord. I could push the Record
> constructor to protected or private and make MultiClass a friend. This is ugly so I think I should 
> drop the factory method in favor of new Record. Like I said the factory method is mainly sugar 
> anyway.
> 
> I'm assuming your ok with dropping the RecordKeeper::createRecord(...). I'll send that
> patch tomorrow.
> 
> Thanks again for taking time to review.
> 
> Garrison 
> 
>> 
> 
>> Some minor coding style things:
>> 
>> ...
> 
>> -Chris
>> 
> 
> <RecordKeeper.4.patch>