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* class.c (finish_struct_1): Add commentary on prevous change. 

From-SVN: r22884
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Mark Mitchell 1998-10-07 09:30:50 +00:00 committed by Mark Mitchell
parent 39828aec68
commit 9335e9a3a1
2 changed files with 21 additions and 2 deletions
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2
gcc/cp/ChangeLog
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@ -1,5 +1,7 @@
1998-10-07 Mark Mitchell <mark@markmitchell.com>
* class.c (finish_struct_1): Add commentary on prevous change.
* cp-tree.h (vtbl_ptr_type_node): New variable.
* class.c (build_vtbl_ref): Don't indirect through the vptr; it's
already of the right type.

21
gcc/cp/class.c
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@ -3777,8 +3777,25 @@ finish_struct_1 (t, warn_anon)
if (vfield == NULL_TREE && has_virtual)
{
/* We build this decl with ptr_type_node, and
change the type when we know what it should be. */
/* We build this decl with vtbl_ptr_type_node, which is a
`vtable_entry_type*'. It might seem more precise to use
`vtable_entry_type (*)[N]' where N is the number of firtual
functions. However, that would require the vtable pointer in
base classes to have a different type than the vtable pointer
in derived classes. We could make that happen, but that
still wouldn't solve all the problems. In particular, the
type-based alias analysis code would decide that assignments
to the base class vtable pointer can't alias assignments to
the derived class vtable pointer, since they have different
types. Thus, in an derived class destructor, where the base
class constructor was inlined, we could generate bad code for
setting up the vtable pointer.
Therefore, we use one type for all vtable pointers. We still
use a type-correct type; it's just doesn't indicate the array
bounds. That's better than using `void*' or some such; it's
cleaner, and it let's the alias analysis code know that these
stores cannot alias stores to void*! */
vfield = build_lang_field_decl (FIELD_DECL, get_vfield_name (t),
vtbl_ptr_type_node);
/* If you change any of the below, take a look at all the