C: allow aliasing of compatible types derived from enumeral types [PR115157]

Aliasing of enumeral types with the underlying integer is now allowed
by setting the aliasing set to zero.  But this does not allow aliasing
of derived types which are compatible as required by ISO C.  Instead,
initially set structural equality.  Then set TYPE_CANONICAL and update
pointers and main variants when the type is completed (as done for
structures and unions in C23).

	PR tree-optimization/115157
	PR tree-optimization/115177

gcc/c/
	* c-decl.cc (shadow_tag-warned,parse_xref_tag,start_enum,
	finish_enum): Set SET_TYPE_STRUCTURAL_EQUALITY / TYPE_CANONICAL.
	* c-objc-common.cc (get_alias_set): Remove special case.
	(get_aka_type): Add special case.

gcc/c-family/
	* c-attribs.cc (handle_hardbool_attribute): Set TYPE_CANONICAL
	for hardbools.

gcc/
	* godump.cc (go_output_typedef): Use TYPE_MAIN_VARIANT instead
	of TYPE_CANONICAL.

gcc/testsuite/
	* gcc.dg/enum-alias-1.c: New test.
	* gcc.dg/enum-alias-2.c: New test.
	* gcc.dg/enum-alias-3.c: New test.
	* gcc.dg/enum-alias-4.c: New test.

8 files changed, 112 insertions, 14 deletions

diff --git a/gcc/c-family/c-attribs.cc b/gcc/c-family/c-attribs.cc
index 605469d..e3833ed 100644
--- a/gcc/c-family/c-attribs.cc
+++ b/gcc/c-family/c-attribs.cc
@@ -1074,6 +1074,7 @@ handle_hardbool_attribute (tree *node, tree name, tree args,
 
   TREE_SET_CODE (*node, ENUMERAL_TYPE);
   ENUM_UNDERLYING_TYPE (*node) = orig;
+  TYPE_CANONICAL (*node) = TYPE_CANONICAL (orig);
 
   tree false_value;
   if (args)
diff --git a/gcc/c/c-decl.cc b/gcc/c/c-decl.cc
index b691b91..6e6606c 100644
--- a/gcc/c/c-decl.cc
+++ b/gcc/c/c-decl.cc
@@ -5051,7 +5051,7 @@ shadow_tag_warned (const struct c_declspecs *declspecs, int warned)
 	      if (t == NULL_TREE)
 		{
 		  t = make_node (code);
-		  if (flag_isoc23 && code != ENUMERAL_TYPE)
+		  if (flag_isoc23 || code == ENUMERAL_TYPE)
 		    SET_TYPE_STRUCTURAL_EQUALITY (t);
 		  pushtag (input_location, name, t);
 		}
@@ -8828,7 +8828,7 @@ parser_xref_tag (location_t loc, enum tree_code code, tree name,
      the forward-reference will be altered into a real type.  */
 
   ref = make_node (code);
-  if (flag_isoc23 && code != ENUMERAL_TYPE)
+  if (flag_isoc23 || code == ENUMERAL_TYPE)
     SET_TYPE_STRUCTURAL_EQUALITY (ref);
   if (code == ENUMERAL_TYPE)
     {
@@ -9919,6 +9919,7 @@ start_enum (location_t loc, struct c_enum_contents *the_enum, tree name,
     {
       enumtype = make_node (ENUMERAL_TYPE);
       TYPE_SIZE (enumtype) = NULL_TREE;
+      SET_TYPE_STRUCTURAL_EQUALITY (enumtype);
       pushtag (loc, name, enumtype);
       if (fixed_underlying_type != NULL_TREE)
 	{
@@ -9935,6 +9936,8 @@ start_enum (location_t loc, struct c_enum_contents *the_enum, tree name,
 	  TYPE_SIZE (enumtype) = NULL_TREE;
 	  TYPE_PRECISION (enumtype) = TYPE_PRECISION (fixed_underlying_type);
 	  ENUM_UNDERLYING_TYPE (enumtype) = fixed_underlying_type;
+	  TYPE_CANONICAL (enumtype) = TYPE_CANONICAL (fixed_underlying_type);
+	  c_update_type_canonical (enumtype);
 	  layout_type (enumtype);
 	}
     }
@@ -10094,6 +10097,10 @@ finish_enum (tree enumtype, tree values, tree attributes)
       ENUM_UNDERLYING_TYPE (enumtype) =
 	c_common_type_for_size (TYPE_PRECISION (tem), TYPE_UNSIGNED (tem));
 
+      TYPE_CANONICAL (enumtype) =
+	TYPE_CANONICAL (ENUM_UNDERLYING_TYPE (enumtype));
+      c_update_type_canonical (enumtype);
+
       layout_type (enumtype);
     }
 
diff --git a/gcc/c/c-objc-common.cc b/gcc/c/c-objc-common.cc
index 42a62c8..283f6a8 100644
--- a/gcc/c/c-objc-common.cc
+++ b/gcc/c/c-objc-common.cc
@@ -130,6 +130,8 @@ get_aka_type (tree type)
 
       result = get_aka_type (orig_type);
     }
+  else if (TREE_CODE (type) == ENUMERAL_TYPE)
+    return type;
   else
     {
       tree canonical = TYPE_CANONICAL (type);
@@ -418,11 +420,6 @@ c_var_mod_p (tree x, tree fn ATTRIBUTE_UNUSED)
 alias_set_type
 c_get_alias_set (tree t)
 {
-  /* Allow aliasing between enumeral types and the underlying
-     integer type.  This is required since those are compatible types.  */
-  if (TREE_CODE (t) == ENUMERAL_TYPE)
-    return get_alias_set (ENUM_UNDERLYING_TYPE (t));
-
   /* Structs with variable size can alias different incompatible
      structs.  Let them alias anything.   */
   if (RECORD_OR_UNION_TYPE_P (t) && C_TYPE_VARIABLE_SIZE (t))
diff --git a/gcc/godump.cc b/gcc/godump.cc
index 66e73ad..6784bd7 100644
--- a/gcc/godump.cc
+++ b/gcc/godump.cc
@@ -1118,10 +1118,8 @@ go_output_typedef (class godump_container *container, tree decl)
      separately.  */
   if (TREE_CODE (TREE_TYPE (decl)) == ENUMERAL_TYPE
       && TYPE_SIZE (TREE_TYPE (decl)) != 0
-      && !container->decls_seen.contains (TREE_TYPE (decl))
-      && (TYPE_CANONICAL (TREE_TYPE (decl)) == NULL_TREE
-	  || !container->decls_seen.contains
-				    (TYPE_CANONICAL (TREE_TYPE (decl)))))
+      && !container->decls_seen.contains
+	    (TYPE_MAIN_VARIANT (TREE_TYPE (decl))))
     {
       tree element;
 
@@ -1163,9 +1161,7 @@ go_output_typedef (class godump_container *container, tree decl)
 	  mhval->value = xstrdup (buf);
 	  *slot = mhval;
 	}
-      container->decls_seen.add (TREE_TYPE (decl));
-      if (TYPE_CANONICAL (TREE_TYPE (decl)) != NULL_TREE)
-	container->decls_seen.add (TYPE_CANONICAL (TREE_TYPE (decl)));
+      container->decls_seen.add (TYPE_MAIN_VARIANT (TREE_TYPE (decl)));
     }
 
   if (DECL_NAME (decl) != NULL_TREE)
diff --git a/gcc/testsuite/gcc.dg/enum-alias-1.c b/gcc/testsuite/gcc.dg/enum-alias-1.c
new file mode 100644
index 0000000..8fa30eb
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/enum-alias-1.c
@@ -0,0 +1,24 @@
+/* { dg-do run } */
+/* { dg-options "-O2" } */
+
+enum E { E1 = -1, E2 = 0, E3 = 1 };
+
+typedef int A;
+typedef enum E B;
+
+_Static_assert(_Generic((A){ 0 }, B: 1), "");
+
+void* foo(void* a, void *b, A *c, B *d)
+{
+	*(A**)a = c;
+	*(B**)b = d;
+	return *(A**)a;
+}
+
+int main()
+{
+	A *a, b, c;
+	if (&c != (A*)foo(&a, &a, &b, &c))
+		__builtin_abort();
+}
+
diff --git a/gcc/testsuite/gcc.dg/enum-alias-2.c b/gcc/testsuite/gcc.dg/enum-alias-2.c
new file mode 100644
index 0000000..7ca3f3b
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/enum-alias-2.c
@@ -0,0 +1,25 @@
+/* { dg-do run } */
+/* { dg-options "-O2" } */
+
+typedef int A;
+
+void* foo(void* a, void *b, void *c, void *d)
+{
+	*(A**)a = c;
+
+	{
+		typedef enum E B;
+		enum E { E1 = -1, E2 = 0, E3 = 1 };
+		*(B**)b = d;
+	}
+
+	return *(A**)a;
+}
+
+int main()
+{
+	A *a, b, c;
+	if (&c != (A*)foo(&a, &a, &b, &c))
+		__builtin_abort();
+}
+
diff --git a/gcc/testsuite/gcc.dg/enum-alias-3.c b/gcc/testsuite/gcc.dg/enum-alias-3.c
new file mode 100644
index 0000000..36a4f02
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/enum-alias-3.c
@@ -0,0 +1,26 @@
+/* { dg-do run } */
+/* { dg-options "-O2 -flto" } */
+
+typedef int *A;
+
+void* foo(void* a, void *b, void *c, void *d)
+{
+	*(A**)a = c;
+
+	typedef enum E *B;
+	enum E { E1 = -1, E2 = 0, E3 = 1 };
+	{
+		*(B**)b = d;
+	}
+
+	return *(A**)a;
+}
+
+int main()
+{
+	A *a, b, c;
+	if (&c != (A*)foo(&a, &a, &b, &c))
+		__builtin_abort();
+}
+
+
diff --git a/gcc/testsuite/gcc.dg/enum-alias-4.c b/gcc/testsuite/gcc.dg/enum-alias-4.c
new file mode 100644
index 0000000..b78d045
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/enum-alias-4.c
@@ -0,0 +1,22 @@
+/* { dg-do run } */
+/* { dg-options "-O2" } */
+
+typedef int A;
+typedef int __attribute__ (( hardbool(0, 1) )) B;
+
+_Static_assert(_Generic((A*){ 0 }, B*: 1), "");
+
+void* foo(void* a, void *b, A *c, B *d)
+{
+        *(A**)a = c;
+        *(B**)b = d;
+        return *(A**)a;
+}
+
+int main()
+{
+        A *a, b, c;
+        if (&c != (A*)foo(&a, &a, &b, &c))
+                __builtin_abort();
+}
+