[C] remove same_translation_unit_p

  Here is a patch to remove the unused function
same_translation_unit_p and related code. The
code to check for structural equivalency of
structs / unions is kept (with some fixes)
because it will be needed for C2X.



    c: Remove dead code related to type compatibility across TUs. 

    Code to detect struct/unions across the same TU is not needed
    anymore. Code for determining compatibility of tagged types is
    preserved as it will be used for C2X. Some errors in the unused
    code are fixed.

    Bootstrapped with no regressions for x86_64-pc-linux-gnu.

    gcc/c/
            * c-decl.cc (set_type_context): Remove.
	    (pop_scope, diagnose_mismatched_decls, pushdecl):
	    Remove dead code.
	    * c-typeck.cc (comptypes_internal): Remove dead code.
	    (same_translation_unit_p): Remove.
	    (tagged_types_tu_compatible_p): Some fixes.




 	  tree a2 = TYPE_ATTRIBUTES (t2);
@@ -1278,11 +1278,11 @@ 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;
 
@@ -1357,40 +1357,7 @@ 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. */
 
@@ -1541,6 +1508,7 @@ 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;
@@ -1619,7 +1587,7 @@ 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;
       }
 
@@ -1627,6 +1595,12 @@ 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))
  

On Tue, 20 Dec 2022, Martin Uecker via Gcc-patches wrote:

> Here is a patch to remove the unused function
> same_translation_unit_p and related code. The
> code to check for structural equivalency of
> structs / unions is kept (with some fixes)
> because it will be needed for C2X.

Could you repost this in development stage 1, since this is not a bug fix?
  

Am Dienstag, dem 20.12.2022 um 20:04 +0000 schrieb Joseph Myers:
> On Tue, 20 Dec 2022, Martin Uecker via Gcc-patches wrote:
> 
> > Here is a patch to remove the unused function
> > same_translation_unit_p and related code. The
> > code to check for structural equivalency of
> > structs / unions is kept (with some fixes)
> > because it will be needed for C2X.
> 
> Could you repost this in development stage 1, since this is not a bug
> fix?

Sure, I will repost for stage 1.

I plan to send some other similar patches with
no functional change (with no expectation that they
get reviewed now) because I like to get some early
feedback rom Martin Liška on some UBsan changes
which are layered on top of them.


Martin