[cfe-dev] [PATCH] Automatic detection of compatibility macros for non-portable diagnostics

[Chandler Carruth]

On Fri, Jul 27, 2012 at 4:07 PM, Alexander Kornienko <alexfh at google.com>wrote:

> On Fri, Jul 27, 2012 at 11:40 PM, Chandler Carruth <chandlerc at google.com>wrote:
>
>> FWIW, at a high level I find the callback approach is very worrisome.
>>
>> The callback system was designed to be fast when the callbacks were
>> completely null, and impose a non-trivial cost on the preprocessor
>> otherwise.
>>
> I do not think that we'll get measurably worse performance as a result of
> this change. This code only works on macro definitions (does anyone know
> how many of those per translation unit should we expect IRL?),
>

Boost provides libraries that do terrifying things here. I don't think we
can count on this number being "small".


> Can we not walk back through the macro definitions after-the-fact? I would
>> expect the preprocessor to still have all the information we need.
>>
> I'm not sure that we retain contents of #undef'ed and redefined macros.
> And we definitely need this as we run analysis after the whole file is
> lexed.
>

But I would expect the macros we're particularly interested in
(compatibility ones) would not be undef'ed anywhere...
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