Re: Is it possible to make gcc detect whether printf prints floating point numbers?

Re: Is it possible to make gcc detect whether printf prints floating point numbers?

[Andrew Haley]

[Redirect to gcc-help]

On 06/08/2012 09:54 AM, Bin.Cheng wrote:
> In micro-controller applications, code size is critical and the size
> problem is worse if library is linked.
> For example, most c programs call printf to format output data, that
> means floating point code get linked even the program only want to
> output non-floating point numbers. Currently, we rely on end-user to
> call iprintf if the program does not want floating point.
>
> I noticed that GCC now can check format string of printf functions, so
> I am wondering if it is possible to take advantage of this utility, by
> making gcc detect whether printf prints floating point number and then
> generate assembly directive in backend to pull in floating point
> functions only if necessary.

It wouldn't be at all difficult, but you'd have to change gcc.

Andrew.

Re: Is it possible to make gcc detect whether printf prints floating point numbers?

[Bin.Cheng]

On Fri, Jun 8, 2012 at 5:14 PM, Andrew Haley <aph@redhat.com> wrote:
> [Redirect to gcc-help]
>
> On 06/08/2012 09:54 AM, Bin.Cheng wrote:
>> In micro-controller applications, code size is critical and the size
>> problem is worse if library is linked.
>> For example, most c programs call printf to format output data, that
>> means floating point code get linked even the program only want to
>> output non-floating point numbers. Currently, we rely on end-user to
>> call iprintf if the program does not want floating point.
>>
>> I noticed that GCC now can check format string of printf functions, so
>> I am wondering if it is possible to take advantage of this utility, by
>> making gcc detect whether printf prints floating point number and then
>> generate assembly directive in backend to pull in floating point
>> functions only if necessary.
>
> It wouldn't be at all difficult, but you'd have to change gcc.
>

Thanks Andrew.
How about the question:
The check is done in front end, so how should I expose the check
result to back-end. Is there any hook utility?

Thanks.
-- 
Best Regards.

Re: Is it possible to make gcc detect whether printf prints floating point numbers?

[Andrew Haley]

On 06/08/2012 10:57 AM, Bin.Cheng wrote:
> On Fri, Jun 8, 2012 at 5:14 PM, Andrew Haley <aph@redhat.com> wrote:
>> [Redirect to gcc-help]
>>
>> On 06/08/2012 09:54 AM, Bin.Cheng wrote:
>>> In micro-controller applications, code size is critical and the size
>>> problem is worse if library is linked.
>>> For example, most c programs call printf to format output data, that
>>> means floating point code get linked even the program only want to
>>> output non-floating point numbers. Currently, we rely on end-user to
>>> call iprintf if the program does not want floating point.
>>>
>>> I noticed that GCC now can check format string of printf functions, so
>>> I am wondering if it is possible to take advantage of this utility, by
>>> making gcc detect whether printf prints floating point number and then
>>> generate assembly directive in backend to pull in floating point
>>> functions only if necessary.
>>
>> It wouldn't be at all difficult, but you'd have to change gcc.
>>
> 
> Thanks Andrew.
> How about the question:
> The check is done in front end, so how should I expose the check
> result to back-end.

I wouldn't.  I'd just call printf or iprintf, depending on the
use of floating-point.

Andrew.