----- Am 15. Aug 2025 um 2:33 schrieb Sebastian Huber
sebastian.hu...@embedded-brains.de:
> ----- Am 15. Aug 2025 um 0:02 schrieb Jeff Law jeffreya...@gmail.com:
>
>> On 8/13/25 9:00 PM, Sebastian Huber wrote:
>>> Hello Jeff,
>>>
>>> thanks for your comment.
>>>
>>> ----- Am 10. Jul 2025 um 16:01 schrieb Jeff Law jeffreya...@gmail.com:
>>>
>>>> On 7/9/25 11:53 PM, Sebastian Huber wrote:
>>>>> There are targets, which only offer 32-bit atomic operations (for
>>>>> example 32-bit RISC-V). For these targets, split the 64-bit atomic
>>>>> bitwise-or operation into two parts.
>>>>>
>>>>> For this test case
>>>>>
>>>>> int a(int i);
>>>>> int b(int i);
>>>>>
>>>>> int f(int i)
>>>>> {
>>>>> if (i) {
>>>>> return a(i);
>>>>> } else {
>>>>> return b(i);
>>>>> }
>>>>> }
>>>>>
>>>>> with options
>>>>>
>>>>> -O2 -fprofile-update=atomic -fcondition-coverage
>> So looking at this again, this is sufficient to show some of the issues.
>> I would file this as a bug. I think the question will turn into
>> whether or not we want the instrumentation code to try and optimize away
>> unnecessary ops or if it should be left to the gimple optimizers.
>>
>> In the opptimized dump we can see stuff like this:
>>
>>> __atomic_fetch_or_8 (&__gcov8.f[1], 0, 0);
>>
>> So that's not going to change the value at &__gcov8.f[1] and we don't
>> use the result, so we don't actually need to do the load either. So
>> this could in theory just be removed at the gimple phase. Or at least
>> that's how it seems to me.
>
> I created a bug report:
>
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121560
This turned out to be a duplicate. From reading this
https://gcc.gnu.org/wiki/Atomic/GCCMM/Optimizations
the optimization potential for relaxed atomic operations seems to be rather
limited.
However, this is just a side track of the patch. The main goal is to be able to
use atomic updates on some 32-bit targets.
--
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