diff -r 000000000000 -r 6474c204b198 xpcom/tests/ShowAlignments.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/xpcom/tests/ShowAlignments.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,38 @@
+/* vim: set shiftwidth=2 tabstop=8 autoindent cindent expandtab: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/* show the size and alignment requirements of various types */
+
+#include "nsMemory.h"
+#include <stdio.h>
+
+struct S {
+  double d;
+  char c;
+  short s;
+};
+
+int main()
+{
+  static const char str[] =
+    "Type %s has size %u and alignment requirement %u\n";
+  #define SHOW_TYPE(t_) \
+    printf(str, #t_, unsigned(sizeof(t_)), unsigned(NS_ALIGNMENT_OF(t_)))
+
+  SHOW_TYPE(char);
+  SHOW_TYPE(unsigned short);
+  SHOW_TYPE(int);
+  SHOW_TYPE(long);
+  SHOW_TYPE(uint8_t);
+  SHOW_TYPE(int16_t);
+  SHOW_TYPE(uint32_t);
+  SHOW_TYPE(void*);
+  SHOW_TYPE(double);
+  SHOW_TYPE(short[7]);
+  SHOW_TYPE(S);
+  SHOW_TYPE(double S::*);
+
+  return 0;
+}