c: [PR32122] Require pointer types for computed gotos

So GCC has always accepted non-pointer types in computed gotos but
that was wrong based on the documentation:
Any expression of type void * is allowed.

So this fixes the problem by requiring the type to
be a pointer type.

OK? Bootstrapped and tested on x86_64-linux-gnu with no regressions.

	PR c/32122

gcc/c/ChangeLog:

	* c-parser.c (c_parser_statement_after_labels): Pass
	the c_expr instead of the tree to c_finish_goto_ptr.
	* c-typeck.c (c_finish_goto_ptr): Change the second
	argument type to c_expr.
	* c-tree.h (c_finish_goto_ptr): Likewise.
	Error out if the expression was not of a pointer type.

gcc/testsuite/ChangeLog:

	* gcc.dg/comp-goto-5.c: New test.
	* gcc.dg/comp-goto-6.c: New test.

gcc/c/c-parser.c

@@ -6141,7 +6141,7 @@ c_parser_statement_after_labels (c_parser *parser, bool *if_p,
 	      c_parser_consume_token (parser);
 	      val = c_parser_expression (parser);
 	      val = convert_lvalue_to_rvalue (loc, val, false, true);
-	      stmt = c_finish_goto_ptr (loc, val.value);
+	      stmt = c_finish_goto_ptr (loc, val);
 	    }
 	  else
 	    c_parser_error (parser, "expected identifier or %<*%>");

gcc/c/c-tree.h

@@ -746,7 +746,7 @@ extern tree c_finish_expr_stmt (location_t, tree);
 extern tree c_finish_return (location_t, tree, tree);
 extern tree c_finish_bc_stmt (location_t, tree, bool);
 extern tree c_finish_goto_label (location_t, tree);
-extern tree c_finish_goto_ptr (location_t, tree);
+extern tree c_finish_goto_ptr (location_t, c_expr val);
 extern tree c_expr_to_decl (tree, bool *, bool *);
 extern tree c_finish_omp_construct (location_t, enum tree_code, tree, tree);
 extern tree c_finish_oacc_data (location_t, tree, tree);

gcc/c/c-typeck.c

@@ -10783,10 +10783,19 @@ c_finish_goto_label (location_t loc, tree label)
    the GOTO.  */
 
 tree
-c_finish_goto_ptr (location_t loc, tree expr)
+c_finish_goto_ptr (location_t loc, c_expr val)
 {
+  tree expr = val.value;
   tree t;
   pedwarn (loc, OPT_Wpedantic, "ISO C forbids %<goto *expr;%>");
+  if (expr != error_mark_node
+      && !POINTER_TYPE_P (TREE_TYPE (expr))
+      && !null_pointer_constant_p (expr))
+    {
+      error_at (val.get_location (),
+		"computed goto must be pointer type");
+      expr = build_zero_cst (ptr_type_node);
+    }
   expr = c_fully_fold (expr, false, NULL);
   expr = convert (ptr_type_node, expr);
   t = build1 (GOTO_EXPR, void_type_node, expr);

gcc/testsuite/gcc.dg/comp-goto-5.c

@@ -0,0 +1,11 @@
+/* PR c/32122 */
+/* { dg-do compile } */
+/* { dg-options "" } */
+
+enum {a=1};
+void foo()
+{
+  goto *
+        a; /* { dg-error "computed goto must be pointer type" } */
+}
+

gcc/testsuite/gcc.dg/comp-goto-6.c

@@ -0,0 +1,6 @@
+/* PR c/32122 */
+/* { dg-do compile } */
+/* { dg-options "" } */
+void foo(void *a) { goto *10000000; } /* { dg-error "computed goto must be pointer type" } */
+void foo1(void *a) { goto *a; }
+