[PATCH] Fix ODR violations in code using <ext/atomicity.h>

[Jonathan Wakely]

On 21/06/19 13:01 -0400, Nathan Sidwell wrote:
>On 6/21/19 12:01 PM, Jonathan Wakely wrote:
>>Nathan noticed that the 'static inline' functions in <ext/atomicity.h>
>>cause ODR violations when used from inline functions or templates (see
>>[basic.def.odr] p12 bullet (12.2)). His modules branch now diagnoses
>>those violations, so we need a fix.
>>
>>Looking at the history (r114044 by Paolo) I believe the idea was indeed
>>to allow different definitions to be used in different TUs. I think
>>__attribute__((__always_inline__)) is a better match for that than
>>'static inline', and doesn't violate the ODR (at least, not if all TUs
>>have the same values for __GTHREADS and _GLIBCXX_ATOMIC_BUILTINS).
>>
>>These functions still violate this rule in [dcl.inline]:
>>
>>C++17: "If a function with external linkage is declared inline in one
>>translation unit, it shall be declared inline in all translation units
>>in which it appears; no diagnostic is required."
>>
>>C++2a WP: "If a function or variable with external or module linkage
>>is declared inline in one translation unit, there shall be a reachable
>>inline declaration in all translation units in which it is declared;
>>no diagnostic is required."
>>
>>But that doesn't seem to be diagnosable by today's implementations.
>>
>>Does this change seem reasonable?
>
>yes, thanks!

Actually, I think I prefer this version. This produces identical code
to the always_inline version, but without the indirection to
additional inline functions, i.e. just inline the relevant code into
the _dispatch functions.

Tests are still running but no failures so far, as expected.


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