intermodule and comptypes - need some help

["Zack Weinberg" <zack at codesourcery dot com>]

A patch I'm working on has, as a side effect, that (in intermodule
mode) duplicate_decls may encounter two declarations from different
translation units at any time, not just during
merge_translation_unit_decls.  It therefore cannot simply be told when
to invoke comptypes with the special COMPARE_DIFFERENT_TU flag.  I
tried to write a function which would detect when two types came from
different translation units, but it doesn't work: --enable-intermodule
bootstrap blows up with tons of spurious duplicate declarations.

This is the code I wrote:-

/* Determine whether two types derive from the same translation unit.
   If the CONTEXT chain ends in a null, that type's context is still
   being parsed, so if two types have context chains ending in null,
   they're in the same translation unit.  */
static int
same_translation_unit_p (tree t1, tree t2)
{
  while (t1 && TREE_CODE (t1) != TRANSLATION_UNIT_DECL)
    switch (TREE_CODE_CLASS (TREE_CODE (t1)))
      {
      case 'd': t1 = DECL_CONTEXT (t1); break;
      case 't': t1 = TYPE_CONTEXT (t1); break;
      case 'b': t1 = BLOCK_SUPERCONTEXT (t1); break;
      default: abort ();
      }

  while (t2 && TREE_CODE (t2) != TRANSLATION_UNIT_DECL)
    switch (TREE_CODE_CLASS (TREE_CODE (t2)))
      {
      case 'd': t2 = DECL_CONTEXT (t1); break;
      case 't': t2 = TYPE_CONTEXT (t2); break;
      case 'b': t2 = BLOCK_SUPERCONTEXT (t2); break;
      default: abort ();
      }


  return t1 == t2;
}

This replaces the flags check guarding the call to
tagged_types_tu_compatible_p.  What am I doing wrong?

zw