[cfe-dev] [PROPOSAL] per-function optimization level control

[Eric Christopher]

Especially since we have support for per function code gen attributes now.

-eric

On Wed, Apr 24, 2013 at 3:50 PM, Richard Smith <richard at metafoo.co.uk> wrote:
> On Wed, Apr 24, 2013 at 6:00 AM, <Andrea_DiBiagio at sn.scee.net> wrote:
>>
>> Hello,
>>
>> We've had a high priority feature request from a number of our customers
>> to
>> provide per-function optimization in our Clang/LLVM compiler.
>> I would be interested in working with the community to implement this.
>> The idea is to allow the optimization level to be overridden
>> for specific functions.
>>
>> The rest of this proposal is organized as follows:
>>  - Section 1. describes this new feature and explains why and when
>>    per-function optimization options are useful;
>>  - Sections 2. and 3. describe how the optimizer could be adapted/changed
>>    to allow the definition of per-function optimizations;
>>  - Section 4. tries to outline a possible workflow for implementing this
>>    new feature.
>>
>> I am looking for any feedback or suggestions etc.
>>
>> Thanks!
>> Andrea Di Biagio
>> SN Systems Ltd.
>> http://www.snsys.com
>>
>> 1. Description
>> ==============
>> The idea is to add pragmas to control the optimization level on functions.
>>
>> A similar approach has been implemented by GCC as well.
>> Since GCC 4.4, new function specific option pragmas have been added to
>> allow
>> users to set the optimization level on a per function basis.
>>
>> http://gcc.gnu.org/onlinedocs/gcc/Function-Specific-Option-Pragmas.html
>> describes the pragmas as
>>   #pragma GCC optimize ("string")
>>   #pragma GCC push_options
>>   #pragma GCC pop_options
>>   #pragma GCC reset_options
>>
>> Instead of imitating GCC's syntax, I think it would be better to use a
>> syntax
>> consistent with existing pragma clang diagnostics:
>>
>>   #pragma clang optimize push
>>   #pragma clang optimize "string"
>>   #pragma clang optimize pop
>
>
> Since the intent is to provide overrides on a per-function basis, have you
> considered using a function attribute instead of a pragma?
>
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