[PATCH] D51789: [clang] Add the exclude_from_explicit_instantiation attribute

[Louis Dionne via Phabricator via cfe-commits]

ldionne added a comment.

In https://reviews.llvm.org/D51789#1238396, @rjmccall wrote:

> That may work for libc++'s purposes, but it's clearly inappropriate as a compiler rule.  There are good reasons why something with hidden visibility would need to be explicitly instantiated.


I take your word for it, but I can't think of any example. For my education, do you have a specific example in mind?

> For many programmers, hidden visibility means "this is private to my library", not "this is actually public to my library, but I'm walking an ABI tightrope".

In libc++'s case, the functions we will annotate with `exclude_from_explicit_instantiation` are private to libc++ too (in the sense that we don't want them part of the ABI and they are not exported from the dylib). Those functions were previously marked with `__always_inline__` to make sure they were not part of the ABI.

Note that I'm quite happy with `exclude_from_explicit_instantiation` as it solves libc++'s problem -- I'm trying to see whether another solution would serve people better while still solving libc++'s problem. (Appart from explicitly exporting functions, typeinfos and vtables like we've talked about on cfe-dev, which is a superior solution to everything else but is left as a future improvement for the time being).


Repository:
  rC Clang

https://reviews.llvm.org/D51789