[C] Remove dead code related to type compatibility across TUs.

diff --git a/gcc/c/c-decl.cc b/gcc/c/c-decl.cc
index f63c1108ab5..70345b4b019 100644
--- a/gcc/c/c-decl.cc
+++ b/gcc/c/c-decl.cc
@@ -1155,16 +1155,6 @@  update_label_decls (struct c_scope *scope)
     }
 }
 
-/* Set the TYPE_CONTEXT of all of TYPE's variants to CONTEXT.  */
-
-static void
-set_type_context (tree type, tree context)
-{
-  for (type = TYPE_MAIN_VARIANT (type); type;
-       type = TYPE_NEXT_VARIANT (type))
-    TYPE_CONTEXT (type) = context;
-}
-
 /* Exit a scope.  Restore the state of the identifier-decl mappings
    that were in effect when this scope was entered.  Return a BLOCK
    node containing all the DECLs in this scope that are of interest
@@ -1253,7 +1243,6 @@  pop_scope (void)
 	case ENUMERAL_TYPE:
 	case UNION_TYPE:
 	case RECORD_TYPE:
-	  set_type_context (p, context);
 
 	  /* Types may not have tag-names, in which case the type
 	     appears in the bindings list with b->id NULL.  */
@@ -1364,12 +1353,7 @@  pop_scope (void)
 	     the TRANSLATION_UNIT_DECL.  This makes same_translation_unit_p
 	     work.  */
 	  if (scope == file_scope)
-	    {
 	      DECL_CONTEXT (p) = context;
-	      if (TREE_CODE (p) == TYPE_DECL
-		  && TREE_TYPE (p) != error_mark_node)
-		set_type_context (TREE_TYPE (p), context);
-	    }
 
 	  gcc_fallthrough ();
 	  /* Parameters go in DECL_ARGUMENTS, not BLOCK_VARS, and have
@@ -2318,21 +2302,18 @@  diagnose_mismatched_decls (tree newdecl, tree olddecl,
 	{
 	  if (DECL_INITIAL (olddecl))
 	    {
-	      /* If both decls are in the same TU and the new declaration
-		 isn't overriding an extern inline reject the new decl.
-		 In c99, no overriding is allowed in the same translation
-		 unit.  */
-	      if ((!DECL_EXTERN_INLINE (olddecl)
-		   || DECL_EXTERN_INLINE (newdecl)
-		   || (!flag_gnu89_inline
-		       && (!DECL_DECLARED_INLINE_P (olddecl)
-			   || !lookup_attribute ("gnu_inline",
-						 DECL_ATTRIBUTES (olddecl)))
-		       && (!DECL_DECLARED_INLINE_P (newdecl)
-			   || !lookup_attribute ("gnu_inline",
-						 DECL_ATTRIBUTES (newdecl))))
-		  )
-		  && same_translation_unit_p (newdecl, olddecl))
+	      /* If the new declaration isn't overriding an extern inline
+		 reject the new decl. In c99, no overriding is allowed
+		 in the same translation unit.  */
+	      if (!DECL_EXTERN_INLINE (olddecl)
+		  || DECL_EXTERN_INLINE (newdecl)
+		  || (!flag_gnu89_inline
+		      && (!DECL_DECLARED_INLINE_P (olddecl)
+			  || !lookup_attribute ("gnu_inline",
+						DECL_ATTRIBUTES (olddecl)))
+		      && (!DECL_DECLARED_INLINE_P (newdecl)
+			  || !lookup_attribute ("gnu_inline",
+						DECL_ATTRIBUTES (newdecl)))))
 		{
 		  auto_diagnostic_group d;
 		  error ("redefinition of %q+D", newdecl);
@@ -3360,18 +3341,11 @@  pushdecl (tree x)
 	 type to the composite of all the types of that declaration.
 	 After the consistency checks, it will be reset to the
 	 composite of the visible types only.  */
-      if (b && (TREE_PUBLIC (x) || same_translation_unit_p (x, b->decl))
-	  && b->u.type)
+      if (b && b->u.type)
 	TREE_TYPE (b->decl) = b->u.type;
 
-      /* The point of the same_translation_unit_p check here is,
-	 we want to detect a duplicate decl for a construct like
-	 foo() { extern bar(); } ... static bar();  but not if
-	 they are in different translation units.  In any case,
-	 the static does not go in the externals scope.  */
-      if (b
-	  && (TREE_PUBLIC (x) || same_translation_unit_p (x, b->decl))
-	  && duplicate_decls (x, b->decl))
+      /* the static does not go in the externals scope.  */
+      if (b && duplicate_decls (x, b->decl))
 	{
 	  tree thistype;
 	  if (vistype)
diff --git a/gcc/c/c-typeck.cc b/gcc/c/c-typeck.cc
index f619e2a67e7..9a5d6e003ca 100644
--- a/gcc/c/c-typeck.cc
+++ b/gcc/c/c-typeck.cc
@@ -1259,7 +1259,7 @@  comptypes_internal (const_tree type1, const_tree type2, bool *enum_and_int_p,
     case ENUMERAL_TYPE:
     case RECORD_TYPE:
     case UNION_TYPE:
-      if (val != 1 && !same_translation_unit_p (t1, t2))
+      if (val != 1 && false)
 	{
 	  tree a1 = TYPE_ATTRIBUTES (t1);
 	  tree a2 = TYPE_ATTRIBUTES (t2);
@@ -1268,11 +1268,11 @@  comptypes_internal (const_tree type1, const_tree type2, bool *enum_and_int_p,
 	      && ! attribute_list_contained (a2, a1))
 	    break;
 
-	  if (attrval != 2)
-	    return tagged_types_tu_compatible_p (t1, t2, enum_and_int_p,
-						 different_types_p);
 	  val = tagged_types_tu_compatible_p (t1, t2, enum_and_int_p,
 					      different_types_p);
+
+	  if (attrval != 2)
+	    return val;
 	}
       break;
 
@@ -1347,40 +1347,7 @@  comp_target_types (location_t location, tree ttl, tree ttr)
 
 /* Subroutines of `comptypes'.  */
 
-/* Determine whether two trees derive from the same translation unit.
-   If the CONTEXT chain ends in a null, that tree's context is still
-   being parsed, so if two trees have context chains ending in null,
-   they're in the same translation unit.  */
-
-bool
-same_translation_unit_p (const_tree t1, const_tree t2)
-{
-  while (t1 && TREE_CODE (t1) != TRANSLATION_UNIT_DECL)
-    switch (TREE_CODE_CLASS (TREE_CODE (t1)))
-      {
-      case tcc_declaration:
-	t1 = DECL_CONTEXT (t1); break;
-      case tcc_type:
-	t1 = TYPE_CONTEXT (t1); break;
-      case tcc_exceptional:
-	t1 = BLOCK_SUPERCONTEXT (t1); break;  /* assume block */
-      default: gcc_unreachable ();
-      }
 
-  while (t2 && TREE_CODE (t2) != TRANSLATION_UNIT_DECL)
-    switch (TREE_CODE_CLASS (TREE_CODE (t2)))
-      {
-      case tcc_declaration:
-	t2 = DECL_CONTEXT (t2); break;
-      case tcc_type:
-	t2 = TYPE_CONTEXT (t2); break;
-      case tcc_exceptional:
-	t2 = BLOCK_SUPERCONTEXT (t2); break;  /* assume block */
-      default: gcc_unreachable ();
-      }
-
-  return t1 == t2;
-}
 
 /* Allocate the seen two types, assuming that they are compatible. */
 
@@ -1531,6 +1498,7 @@  tagged_types_tu_compatible_p (const_tree t1, const_tree t2,
     case UNION_TYPE:
       {
 	struct tagged_tu_seen_cache *tu = alloc_tagged_tu_seen_cache (t1, t2);
+
 	if (list_length (TYPE_FIELDS (t1)) != list_length (TYPE_FIELDS (t2)))
 	  {
 	    tu->val = 0;
@@ -1609,7 +1577,7 @@  tagged_types_tu_compatible_p (const_tree t1, const_tree t2,
 		return 0;
 	      }
 	  }
-	tu->val = needs_warning ? 2 : 10;
+	tu->val = needs_warning ? 2 : 1;
 	return tu->val;
       }
 
@@ -1617,6 +1585,12 @@  tagged_types_tu_compatible_p (const_tree t1, const_tree t2,
       {
 	struct tagged_tu_seen_cache *tu = alloc_tagged_tu_seen_cache (t1, t2);
 
+	if (list_length (TYPE_FIELDS (t1)) != list_length (TYPE_FIELDS (t2)))
+	  {
+	    tu->val = 0;
+	    return 0;
+	  }
+
 	for (s1 = TYPE_FIELDS (t1), s2 = TYPE_FIELDS (t2);
 	     s1 && s2;
 	     s1 = DECL_CHAIN (s1), s2 = DECL_CHAIN (s2))