[cfe-dev] Applying custom filters after preprocessing (and compile-time sprintf optimization)

[Kazuho Oku]

2014-10-03 9:31 GMT+09:00 Richard Smith <richard at metafoo.co.uk>:

> On Thu, Oct 2, 2014 at 5:18 PM, Kazuho Oku <kazuhooku at gmail.com> wrote:
>
>> Hi,
>>
>> Recently I have started writing a preprocessor that wraps the C
>> preprocessor for optimizing calls to sprintf, since it is the one of the
>> bottlenecks of my application.
>> https://github.com/kazuho/qrintf
>>
>> For GCC, it was easy for me to override the default C preprocessor, by
>> using its `-no-integrated-cpp` and `-wrapper` options (how I have done it
>> can be found in the `qrinf-gcc` and `qrintf-gcc-wrapper` files included in
>> the above repository).
>>
>> However I have so far been unable to find a similar command-line option
>> for Clang.  Is there any way to post-process the output of the preprocessor
>> in Clang?  Or do I need to modify the source code of Clang itself?
>>
>> Thank you in advance.
>>
>> PS. BTW it would be great if compile-time optimization of sprintf goes
>> into Clang.  Is there any chance of such possibility?
>>
>
> In the general case, it's not possible to optimize sprintf fully, because
> its behavior depends on the current locale (this affects %d and %u, which
> it looks like you optimize) and it might have libc-specific extensions, but
> LLVM does optimize in some simple cases: for instance, a sprintf containing
> no % is optimized into memcpy. I expect patches would be accepted to
> implement further cases, such as handling %s and %c.
>

Thank you for the response.  I am delighted to hear that.

I had thought that %d and %u weren't affected by the locale (since the
digits 0..9 and non-monetary use of positive/negative signs are IMO not
locale-dependent).

-- 
Kazuho Oku
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