[cfe-dev] ASTMatchers.h and its internal linkage variable definitions

Manuel Klimek via cfe-dev cfe-dev at lists.llvm.org
Tue Nov 14 01:03:59 PST 2017

On Tue, Nov 14, 2017, 12:53 AM David Blaikie <dblaikie at gmail.com> wrote:

> Ping?
> Richard & I decided that supporting this particular case of
> namespace-scope static variables in modular headers using modular codegen.

Part of the sentence is missing?

(specifically the case where the namespace-scope static variable is
> referenced from an inline function - thus making a true ODR violation (in
> classic C++ this'd be an ODR violation if more than one TU used that header
> - so it seems OK to not support this in modular codegen))

Calling is not an odr use, right? And I thought referencing alone doesn't
lead to an odr violation?

If the namespace-scoped static variable is unreferenced from inline
> functions, that's fine - such as the iostreams global initializer.
> I'll send a CR to move these definitions out of line.

I'm happy with that, too. I assume once c++17 hits the shelves we'll be
able to replace it anyway?

On Thu, Nov 9, 2017 at 12:30 AM Manuel Klimek <klimek at google.com> wrote:
>> On Thu, Nov 9, 2017 at 12:43 AM David Blaikie <dblaikie at gmail.com> wrote:
>>> Hey Manuel,
>>> In an effort to apply Modular Code Generation to Clang internally, I
>>> came across the fact that this header contains a bunch of internal linkage
>>> variables. (now, maybe modular code generation should be compatible with
>>> internal linkage namespace-scoped variables... I'm looking into that)
>>> These variables technically create ODR violations any time they're
>>> ODR-used in another inline function used in more than one translation unit.
>>> Is there a good way we could fix this header so it doesn't create ODR
>>> violations (hopefully by not containing internal linkage entities)? I mean
>>> one simple solution is to declare all these things in a header and define
>>> them out of line. Since they have no actual state, that's probably pretty
>>> low-cost except for a lot of duplication. I'm happy to use a .def/.inc file
>>> to help remove a bunch of that duplication, if useful.
>> I remember having that argument a long time ago with somebody (perhaps
>> Sam (cc'ed)?)
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