Re: Use coroutines for avr-gcc

[Iain Sandoe <idsandoe@googlemail.com>]

> On 22 Sep 2022, at 13:34, Jonathan Wakely <jwakely.gcc@gmail.com> wrote:
> 
> On Thu, 22 Sept 2022 at 13:29, Wilhelm Meier wrote:
>> 
>> According to the standard, an implementation can avoid the
>> heap-allocation, if
>> - the lifetime of the coroutine is strictly within the lifetime of the
>> caller
>> - the size of coroutine state can be determined at compile time
>> 
>> Looks like this optimization is not yet available because new/delete-ops
>> are required.

You can provide your own allocation and deallocation functions in the promise
class :

see  -  https://eel.is/c++draft/dcl.fct.def.coroutine#9
(and #12).

NOTE: this link is the current C++23 draft, the implementation in GCC follows the
C++20 version (but the basic provision is stil there)

>> 
>> Is there any work on this topic?
> 
> The so-called HALO optimizations are much more difficult than was
> originally thought when the wording in the standard was written.
> 
> https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p2477r3.html#background-and-motivation
> describes some of the problems.

Agreed, this topic needs more consideration (and it is not mandatory, so should not be relied upon
for the use-case described in any event).

cheers
Iain

> 
> 
>> Thanks!
>>  Wilhelm
>> 
>> On 21.09.22 15:38, Wilhelm Meier wrote:
>>> I tried to use coroutines with avr-gcc (13.0.0) for the AVR target. I
>>> managed to include the coroutine-header and to write a very simple
>>> generator using the example from cppreference.
>>> 
>>> It compiles well, but then I get undefined symbols:
>>> 
>>> 1) new and delete operator-functions
>>> 2) f(f()::f().Frame*)
>>> 
>>> Therefore two question arise here:
>>> 
>>> a) is it possible to use coroutines without head-allocation? E.g. define
>>> some global storage for the state of the coroutine?
>>> b) if a) can be fullfilled, what is 2) supposed to do?
>>> 
>>> Thanks for any hints,
>>>  Wilhelm