[patch] Fix linkage computation for derived types in inline functions

[John McCall]

On May 22, 2013, at 9:10 PM, Rafael Espíndola <rafael.espindola at gmail.com> wrote:
> John noticed that the fix for pr15930 (r181981) didn't handle indirect
> uses of local types. For example, a pointer to local struct, or a
> function that returns it.
> 
> One way to implement this would be to recursively look for local
> types. This would look a lot like the linkage computation itself for
> types.
> 
> To avoid code duplication and utilize the existing linkage cache, this
> patch just makes the computation of "type with no linkage but
> externally visible because it is from an inline function"  part of the
> linkage computation itself.

Hmm, there's a subtle change in assumptions here, because the
linkage enum is no longer a simple continuum.

Previously, merging two linkages just meant taking their minimum.
For example, consider the type T(*)(U):
  - it has no linkage if either T or U has no linkage; or else
  - it has internal linkage if either T or U has internal linkage; or else
  - it has unique external linkage if either T or U has unique external
    linkage; or else
  - it has external linkage.

But if T has VisibleNoLinkage and U has NoLinkage, InternalLinkage,
or UniqueExternalLinkage, then T(*)(U) has NoLinkage.

(This is slightly artificial; IIRC, the notion of types having linkage is
not in the standard.  But it's the right computation for rules that *are*
in the standard directly, like "template arguments can't involve a
declaration lacking external linkage".)

Also, did you check that all of the bit-fields you increased still pack
efficiently?

John.