Re: [cxx-abi-dev] Mangling of anonymous unions?

[Mark Mitchell <mark@xxxxxxxxxxxxxxxx>]

--On Wednesday, December 18, 2002 04:24:45 PM -0800 Kerch Holt 
<kerch@xxxxxxxxxx> wrote:
> Jason Merrill wrote:
> > On Wed, 18 Dec 2002 15:32:04 -0800, Kerch Holt <kerch@xxxxxxxxxx> wrote:
> >
> >
> > > Wouldn't you need some type of factoring of all the members of the union
> > > (instead of first/last) to avoid collisions (of similar unions in the
> > > same inline)?
> >
> > I'm not sure what you mean.  You would mangle it like any other local
> > variable; if there are more than one with the same name, you need to use
> > a discriminator to distinguish between them.  The only question is which
> > name to use.
> Never mind. I was concerned that two different anonymous union types
> would have the same mangling, but, as you point out if the variable is
> always factored in the mangling will differ.
> Perhaps depending on the ordering (first, last) is problematical... are
> these the same type:
> union { int a; char b; }
> union ( char b; int a; }
They're not the same type, but they can't both be declared in the same
scope, so we're OK.

I can never remember if a union has to have any named members.  Is:

union { int : 7; };

legal?  I think so -- but there's no way to talk about such a thing,
so I suppose its mangled name doesn't matter, but it would be nice
if we had one.

This case:

 union { union { int i; }; };

is legal, so the name-based approach needs a recursive formulation.

I think that the first name found in a pre-order, depth-first,
declaration-order walk is a reasonable choice.

--
Mark Mitchell                mark@xxxxxxxxxxxxxxxx
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