[cfe-dev] Where do we really need mangled names

[David Blaikie]

On Mon, Feb 17, 2014 at 10:16 AM, Adrian Prantl <aprantl at apple.com> wrote:

>
> On Feb 15, 2014, at 17:25, Eric Christopher <echristo at gmail.com> wrote:
>
> > On Sat, Feb 15, 2014 at 2:57 PM, David Blaikie <dblaikie at gmail.com>
> wrote:
> >> So when comparing Clang's debug info strings to GCC's I came across a
> couple
> >> of disparities hinging on the inclusion of linkage names on certain
> >> functions. Here are a few differences:
> >>
> >> * Clang includes linkage names on file-local (static or anon namespace)
> >> functions. GCC does not.
> >> * Clang does not include the linkage name of member functions of
> >> function-local classes. GCC does, if the function is
> >> non-static/non-anonymous namespace and inline (ie: the member function
> has
> >> linkonce-odr linkage, not internal linkage)
> >> * Clang does not include the linkage name for constructors and
> destructors -
> >> this may be necessary due to the difference (GCC duplicates, Clang has
> one
> >> version call the other) in implementations, but I doubt it. I assume we
> >> still emit multiple member functions, one to describe each version of
> the
> >> ctor/dtor we're emitting.
> >>
> >> It looks like at least for the first case, this may've been deliberate (
> >> http://llvm.org/viewvc/llvm-project?view=revision&revision=154570 which
> >> doesn't explain why and points to rdar://11079003 which Jim Grosbach
> told
> >> didn't have a great deal more context) but I don't have enough context
> to
> >> understand why and whether it's just a GCC bug that they don't emit it,
> or
> >> something tools should handle better, etc.
> >>
> >> So - any thoughts on the disparity and if/why it's necessary?
> >>
> >
> > My thought is that it is basically there to assist in lookup of
> > symbols. I put the earlier patch in because it was seen as useful
> > there. In general I find that mangled names are helpful on any entity
> > that we might want to put into a lookup table since we might have a
> > qualified name that we'd like to look up. I doubt that any
> > discrepancies here are intentional, but that any time we have a
> > mangled name we probably want to add it.
>
> And regarding the change r154570, the summary of that radar is that there
> was a mangled name for a static function in the symbol table, but the
> debugger could not look it up in the DWARF because the mangled name was not
> mentioned there.


Could you try a similar experiment with a constructor/destructor (we don't
emit linkage_name for them, but GCC does) and with member functions of
function-local classes (both in an inline/linkonce-odr function and an
external linkage function - GCC would only put the linkage_name on the
former, not the latter, I believe (because the former's member function has
linkonce-odr linkage and the latter should be internal linkage))?

It'd be nice to get these things consistent.

- David
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