Local optimization options

[Marc Glisse]

On Sun, 5 Jul 2020, Thomas König wrote:

>
>> Am 04.07.2020 um 19:11 schrieb Richard Biener <richard.guenther@gmail.com>:
>>
>> On July 4, 2020 11:30:05 AM GMT+02:00, "Thomas König" <tk@tkoenig.net> wrote:
>>>
>>> What could be a preferred way to achieve that? Could optimization
>>> options like -ffast-math be applied to blocks instead of functions?
>>> Could we set flags on the TREE codes to allow certain optinizations?
>>> Other things?
>>
>> The middle end can handle those things on function granularity only.
>>
>> Richard.
>
> OK, so that will not work (or not without a disproportionate
> amount of effort).  Would it be possible to set something like a
> TREE_FAST_MATH flag on TREEs? An operation could then be
> optimized according to these rules iff both operands
> had that flag, and would also have it then.

In order to support various semantics on floating point operations, I was 
planning to replace some trees with internal functions, with an extra 
operand to specify various behaviors (rounding, exception, etc). Although 
at least in the beginning, I was thinking of only using those functions in 
safe mode, to avoid perf regressions.

https://gcc.gnu.org/pipermail/gcc-patches/2019-August/527040.html

This may never happen now, but it sounds similar to setting flags like 
TREE_FAST_MATH that you are suggesting. I was going with functions for 
more flexibility, and to avoid all the existing assumptions about trees. 
While I guess for fast-math, the worst the assumptions could do is clear 
the flag, which would make use optimize less than possible, not so bad.

-- 
Marc Glisse