Re: [C++ PATCH] Battle of the comptypes (PR c++/35049)

["Doug Gregor" <doug.gregor@gmail.com>]

Once I get the O.K. from a C++ front end maintainer to commit this,
yes; I'll include that new test case.

  - Doug

On Feb 6, 2008 10:50 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
> Hi Doug,
>
> Can you include a testcase from
>
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35096
>
>
> H.J.
>
> On Feb 5, 2008 9:52 AM, Doug Gregor <doug.gregor@gmail.com> wrote:
> > PR c++/35049 is a 4.3 regression where we are failing to emit an error
> > when performing addition of vector types that don't have the same base
> > type. The bug seems to have been triggered by a recent change in the
> > canonical types system, but in fact it's been a ticking time bomb for
> > a while. The bug shows up on i386-apple-darwin9.1.0 and (for some
> > people) on i686-pc-linux-gnu
> >
> > The C front end declares the function comptypes like this, in c-tree.h:
> >
> >   extern int comptypes(tree, tree);
> >
> > Parts of the C front end and the C/C++ commit bits use this comptypes.
> > However, this comptypes actually resides in c-typeck.c, which is not
> > linked into the C++ compiler.
> >
> > The C++ front end declares comptypes like this, in cp-tree.h:
> >
> >   extern int comptypes(tree, tree, int);
> >
> > That int is the "strict" parameter, that tells the routine how to
> > compare the types, e.g., strict comparison, checking for base and
> > derived, derived and base, or redeclarations.
> >
> > The fun comes in where the C/C++ common bits call comptypes with 2
> > arguments (as they should), but that ends up calling the C++
> > comptypes... with random data for the "strict" argument. So sometimes
> > we'll get strict comparisons (if that parameter is zero), sometimes
> > we'll get comparisons based on derived/base matching, etc. Most likely
> > this didn't matter before because the C bits don't deal with such C++
> > types often, but in the case of this bug we're thwarting the canonical
> > type system (which is only enabled with strict==COMPARE_STRICT) and
> > getting the wrong answer from comptypes.
> >
> > This patch just renames "comptypes" in the C++ front end to
> > "cp_comptypes", and adds a 2-argument "comptypes" function to the C++
> > front end that accepts calls from the C/C++ common bits and forwards
> > on to cp_comptypes.
> >
> > Tested i386-apple-darwin9.1.0; okay for mainline?
> >
> >   - Doug
> >
> > 2008-02-05  Douglas Gregor  <doug.gregor@gmail.com>
> >
> >         PR c++/35049
> >         * typeck.c (structural_comptypes): Call cp_comptypes.
> >         (comptypes): New; called from the C/C++ common bits to perform
> >         strict checks.
> >         (cp_comptypes): Renamed from comptypes, which is already used,
> >         with a different signature, by the C++ front end.
> >         (build_reinterpret_cast_1): Call cp_comptypes.
> >         (ptr_reasonably_similar): Ditto.
> >         * decl.c (decls_match): Ditto.
> >         * cvt.c (convert_to_reference): Ditto.
> >         * cp-tree.h (same_type_p): Ditto.
> >         (same_or_base_type_p): Ditto.
> >         (comptypes): Rename to cp_comptypes.
> >         * pt.c (canonical_type_parameter): Call cp_comptypes.
> >
>