gc.c: avoid integer overflow at process exit

This is rather nitpicking but at the moment the process terminates,
heap_pages_final_slots overflows.

(lldb) bt
* thread #1: tid = 0xc0903, 0x00000001002b3bf7 miniruby`finalize_list(objspace=0x0000000101c09240, zombie=4329149840) + 999 at gc.c:2946, queue = 'com.apple.main-thread', stop reason = EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0)
  * frame #0: 0x00000001002b3bf7 miniruby`finalize_list(objspace=0x0000000101c09240, zombie=4329149840) + 999 at gc.c:2946
    frame #1: 0x000000010026a69e miniruby`rb_objspace_call_finalizer(objspace=0x0000000101c09240) + 7118 at gc.c:3092
    frame #2: 0x0000000100268ac5 miniruby`rb_gc_call_finalizer_at_exit + 149 at gc.c:3015
    frame #3: 0x00000001002272bc miniruby`ruby_finalize_1 + 156 at eval.c:146
    frame #4: 0x00000001002282b6 miniruby`ruby_cleanup(ex=0) + 4070 at eval.c:238
    frame #5: 0x0000000100228785 miniruby`ruby_run_node(n=0x0000000102060ad8) + 85 at eval.c:317
    frame #6: 0x0000000100000b9c miniruby`main(argc=2, argv=0x00007fff5fbfdc38) + 124 at main.c:42
    frame #7: 0x00007fff9966a5ad libdyld.dylib`start + 1
    frame #8: 0x00007fff9966a5ad libdyld.dylib`start + 1
(lldb) p objspace->heap_pages
(rb_objspace::(anonymous struct)) $0 = {
  sorted = 0x0000000101c070b0
  allocated_pages = 24
  allocatable_pages = 0
  sorted_length = 24
  range = {
    [0] = 0x0000000102020028
    [1] = 0x00000001020dbfd0
  }
  freeable_pages = 0
  final_slots = 0
  deferred_final = 4329149840
}
(lldb)




git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@65633 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

Author: shyouhei

gc.c

@@ -2943,7 +2943,7 @@ finalize_list(rb_objspace_t *objspace, VALUE zombie)
 	run_final(objspace, zombie);
 
 	RZOMBIE(zombie)->basic.flags = 0;
-	heap_pages_final_slots--;
+	if (LIKELY(heap_pages_final_slots)) heap_pages_final_slots--;
 	page->final_slots--;
 	page->free_slots++;
 	heap_page_add_freeobj(objspace, GET_HEAP_PAGE(zombie), zombie);