[libcxx-commits] [libcxx] [libc++] Add __detected_or_t and use it to implement some of the allocator traits aliases (PR #115654)

[David Blaikie via libcxx-commits]

dwblaikie wrote:

> Is there a reason we should ever not put a `_LIBCPP_NODEBUG` on internal aliases?

Don't think so?

> I don't really see how this could have anything to do with anything but aliases, since the number of struct instantiations shouldn't change.

Instantiations don't directly cause DWARF to be emitted - the instantiation has to be referenced by something, so avoiding references to the struct instantiation can reduce the debug info size cost.

Specifically, putting `_LIBCPP_NODEBUG` on the `type` member of a type trait struct avoids needing to describe the struct (to put the `type` member inside of it), which saves a bunch of DWARF. Non-member aliases are nice to attribute too/nice to avoid describing in the DWARF - but the struct types are especially expensive/more verbose than non-member aliases.


https://github.com/llvm/llvm-project/pull/115654