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

["Doug Gregor" <doug dot gregor at gmail dot com>]

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.

Attachment: cp_comptypes.patch
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