[Bug target/60336] empty struct value is passed differently in C and C++

[ubizjak at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60336

--- Comment #17 from Uroš Bizjak <ubizjak at gmail dot com> ---
(In reply to Jason Merrill from comment #15)

> That only documents that sizeof is different for C and C++, the calling
> convention should be the same.  And it seems like classify_argument should
> already be returning 1 with classes[0]==NO_CLASS for both C and C++.  Why
> are we getting different results?

classify_argument has an early exit:

      /* Zero sized arrays or structures are NO_CLASS.  We return 0 to
     signalize memory class, so handle it as special case.  */

      if (!words)
    {
      classes[0] = X86_64_NO_CLASS;
      return 1;
    }

but it doesn't trigger for c++, where words gets calculated as 1.