[llvm] r211595 - Pass a unique_ptr<MemoryBuffer> to the constructors in the Binary hierarchy.

[Rafael Espíndola]

> Agree, we don't need to refcount in many cases where a reference or pointer
> will do. delete/unique_ptr continues to work in those cases, like the
> snippet in my previous mail.

You started this thread saying it was a problem to use unique_ptr. I
am confused.

Lets be clear, if the only case that needs reference counting are some
files in clang, only those should get a reference count. Why not just
use a shared_ptr in there? I *really* don't want to see reference
counting being force into users that don't need it.

>> Is there a case where we copy the buffer that is used for an ObjectFile?
>
>
> materializeAllPermanently() is called right now to avoid the copy. It avoids
> memory duplication, but at a high cost of having to do lots of work early on
> regardless of whether it's going to be used.
>
> The new scheme will get rid of that early materialization so construction
> becomes a trivial operation, and any materialization can happen on-demand,
> for instance in a in a separate compilation/linking phase.
>
> You know the details better, but I imagine in some cases the materialization
> can probably be avoided completely for LTO.

Not with ld64. That was added because of an specific optimation, it
has nothing to do with avoid copies.

Cheers,
Rafael