[gcc r11-8523] c++: fix modules binfo merging

[Jason Merrill <jason@gcc.gnu.org>]

https://gcc.gnu.org/g:03346eb2ccd72fcc0ebe71a5b12e850078ec10ab

commit r11-8523-g03346eb2ccd72fcc0ebe71a5b12e850078ec10ab
Author: Jason Merrill <jason@redhat.com>
Date:   Mon Jun 7 17:51:24 2021 -0400

    c++: fix modules binfo merging
    
    My coming fix for PR91706 caused some regressions in the modules testsuite.
    This turned out to be because the change to properly use the base subobject
    BINFO as BASELINK_BINFO hit problems with the code for merging binfos.  The
    tree reader needed a typo fix.  The duplicate_hash function was crashing on
    the BINFO for a variadic base in <variant>.  I started fixing the hash
    function, but then noticed that there's no ::equal function defined;
    duplicate_hash just uses pointer equality, so we might as well also
    use the normal pointer hash for the moment.
    
    gcc/cp/ChangeLog:
    
            * module.cc (duplicate_hash::hash): Comment out.
            (trees_in::tree_value): Adjust loop counter.

Diff:
---
 gcc/cp/module.cc | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
index 02c19f55548..b97b1bcb2f8 100644
--- a/gcc/cp/module.cc
+++ b/gcc/cp/module.cc
@@ -2820,12 +2820,16 @@ struct merge_key {
 
 struct duplicate_hash : nodel_ptr_hash<tree_node>
 {
+#if 0
+  /* This breaks variadic bases in the xtreme_header tests.  Since ::equal is
+     the default pointer_hash::equal, let's use the default hash as well.  */
   inline static hashval_t hash (value_type decl)
   {
     if (TREE_CODE (decl) == TREE_BINFO)
       decl = TYPE_NAME (BINFO_TYPE (decl));
     return hashval_t (DECL_UID (decl));
   }
+#endif
 };
 
 /* Hashmap of merged duplicates.  Usually decls, but can contain
@@ -8909,7 +8913,7 @@ trees_in::tree_value ()
 	  dump (dumper::MERGE)
 	    && dump ("Deduping binfo %N[%u]", type, ix);
 	  existing = TYPE_BINFO (type);
-	  while (existing && ix)
+	  while (existing && ix--)
 	    existing = TREE_CHAIN (existing);
 	  if (existing)
 	    register_duplicate (t, existing);