Re: mongodb4 on aarch64

[Greg Troxel <gdt%lexort.com@localhost>]

Martin Husemann <martin%duskware.de@localhost> writes:

> I think the flag is new in gcc12.
>
> It makes the compiler change the value of __GCC_DESTRUCTIVE_SIZE, which
> gets it default from the CPU selected by -mtune=... (but only in C++17
> or newer mode).
>
> You can check the value like this:
>
> 	touch /tmp/empty.cpp
> 	c++ -std=c++17 -dM -E /tmp/empty.cpp | fgrep STRUCTIVE
>
> and if the compiler does not define that macro, you could skip the option.

Sure, but that requires writing and patching a configure test into the
upstream code.  I left at todo

> The C++ library uses that macro for a stupid feature in the C++17 standard,
> std::hardware_destructive_interference_size.

THanks for the explanation - stuck in comments to help the next person.