Re: mongodb4 on aarch64

[Martin Husemann <martin%duskware.de@localhost>]

On Mon, Sep 23, 2024 at 09:04:55PM -0400, Greg Troxel wrote:
> I am inclined to drop this flag addition because building on 10 is more
> important than current (at least for the branch), and we can add it back
> based on gcc version or somehow, for systems that need it, once we
> understand more about what's going on.

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.

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

Martin