Go patch committed: Use a different identity function for type hashes

diff -r ae613f1c42f3 go/types.cc
--- a/go/types.cc	Tue Dec 14 22:24:46 2010 -0800
+++ b/go/types.cc	Wed Dec 15 10:21:08 2010 -0800
@@ -393,6 +393,38 @@ 
     }
 }
 
+// Return true if two types are identical when it comes to storing
+// them in a hash table.  This differs from Type::are_identical with
+// regard to how we handle error types.  We want to treat error types
+// as identical to other types when it comes to reporting
+// compatibility errors, but we want to treat them as different when
+// it comes to storing them in a hash table.
+
+bool
+Type::are_identical_for_hash_table(const Type* t1, const Type *t2)
+{
+  if (t1 == NULL || t2 == NULL)
+    return t1 == t2;
+
+  t1 = t1->forwarded();
+  t2 = t2->forwarded();
+
+  if (t1 == t2)
+    return true;
+
+  // Undefined forward declarations are only equal to themselves.
+  if (t1->forward_declaration_type() != NULL
+      || t2->forward_declaration_type() != NULL)
+    return false;
+
+  // The error type is only equal to the error type.
+  if (t1->is_error_type() || t2->is_error_type())
+    return t1->is_error_type() && t2->is_error_type();
+
+  // Otherwise we can use the usual identity check.
+  return Type::are_identical(t1, t2, NULL);
+}
+
 // Return true if it's OK to have a binary operation with types LHS
 // and RHS.  This is not used for shifts or comparisons.
 
@@ -810,14 +842,6 @@ 
 
   tree t = this->get_tree_without_hash(gogo);
 
-  // Don't store errors in the hash table.  This type might be a
-  // pointer to an error type or something like that.  Since error
-  // types are identical to everything else, that could cause us to
-  // return error_mark_node for pointers to any type, which will then
-  // confuse us later.
-  if (t == error_mark_node)
-    return error_mark_node;
-
   if (ins.first->second == NULL_TREE)
     ins.first->second = t;
   else
diff -r ae613f1c42f3 go/types.h
--- a/go/types.h	Tue Dec 14 22:24:46 2010 -0800
+++ b/go/types.h	Wed Dec 15 10:21:08 2010 -0800
@@ -508,6 +508,12 @@ 
   static bool
   are_identical(const Type* lhs, const Type* rhs, std::string* reason);
 
+  // Return true if two types are identical when it comes to putting
+  // them in a hash table.  This differs from are_identical only in
+  // how error types are handled.
+  static bool
+  are_identical_for_hash_table(const Type*, const Type*);
+
   // Return true if two types are compatible for use in a binary
   // operation, other than a shift, comparison, or channel send.  This
   // is an equivalence relation.
@@ -1104,7 +1110,7 @@ 
  public:
   bool
   operator()(const Type* t1, const Type* t2) const
-  { return Type::are_identical(t1, t2, NULL); }
+  { return Type::are_identical_for_hash_table(t1, t2); }
 };
 
 // An identifier with a type.