[gcc r12-1271] c++: fix modules binfo merging

[Jason Merrill]

https://gcc.gnu.org/g:715614ec3ec5390293e508bb190335d28db1fa8b

commit r12-1271-g715614ec3ec5390293e508bb190335d28db1fa8b
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 f0fb0144706..f259515a498 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
@@ -8908,7 +8912,7 @@ 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);