Re: Could __builtin_printf parameters be optimized when being compiled

[Jonny Grant <jg@jguk.org>]

On 15/02/2023 15:49, Segher Boessenkool wrote:
> On Wed, Feb 15, 2023 at 03:10:15PM +0000, Jonny Grant wrote:
>> On 15/02/2023 14:30, Richard Earnshaw wrote:
>>>> int main()
>>>> {
>>>>      __builtin_printf("file %s:%d", __FILE__, __LINE__);
>>>> }
> 
> Note that the format needs to end in "\n" if you want this to be
> converted to a puts() call.  Without it it strangely doesn't seem to
> be optimised, although fprintf() is converted to fwrite() in such cases.
> This could be done for printf() as well: you are guaranteed to have
> access to stdout as well, at least if you use printf() instead of the
> builtin (I'm not sure if we do then).
> 
>>> I guess it might be possible to handle cases where all the arguments are constant, but even that has its problems, eg:
>>>
>>> - can we guarantee identical output to the platform printf?
>>
>> That's a good question. I was using __builtin_printf so that should be GCC I expect.
> 
> Not every printf() implementation has exactly the same output in all
> cases.
> 
> Another practically important consideration is what it does to i18n.
> You really need to leave the format string unmodified for that to be
> able to work.
Thank you for your reply. i18n is a good point. At the moment I was just trying to get some strings for debugging in.

Kind regards
Jonny