[Bug libstdc++/80335] perf of copying std::optional<trivial>

[sgunderson at bigfoot dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80335

--- Comment #3 from sgunderson at bigfoot dot com ---
Appears to have been fixed in GCC 8, indeed.

#include <optional>

std::optional<long> func()
{
        return 3;
}

GCC 7 (-O2) compiles to:

   0:   48 89 f8                mov    %rdi,%rax
   3:   c7 07 03 00 00 00       movl   $0x3,(%rdi)
   9:   c6 47 04 01             movb   $0x1,0x4(%rdi)
   d:   c3                      retq   

GCC 8 (-O2):

   0:   48 b8 03 00 00 00 01    movabs $0x100000003,%rax
   7:   00 00 00 
   a:   c3                      retq   

This is an ABI break, but I'll happily take it. :-)