This commit introduces a new macro, _LIBCPP_HIDE_FROM_ABI, whose goal is to
mark functions that shouldn't be part of libc++'s ABI. It marks the functions
as being hidden for dylib visibility purposes, and as having internal linkage
using Clang's attribute((internal_linkage)) when available, and
It replaces _LIBCPP_INLINE_VISIBILITY, which was always using always_inline
to achieve similar goals, but suffered from debuggability and code size problems.
The full proposal, along with more background information, can be found here:
This commit does not rename uses of _LIBCPP_INLINE_VISIBILITY to
_LIBCPP_HIDE_FROM_ABI: this wide reaching but mechanical change can
be done later when we've confirmed we're happy with the new macro.
In the future, it would be nice if we could optionally allow dropping
any internal_linkage or always_inline attribute, which could result
in code size improvements. However, this is currently impossible for
reasons explained here: http://lists.llvm.org/pipermail/cfe-dev/2018-July/058450.html