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

2018-06-16 Thread 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 

std::optional func()
{
return 3;
}

GCC 7 (-O2) compiles to:

   0:   48 89 f8mov%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 01movabs $0x10003,%rax
   7:   00 00 00 
   a:   c3  retq   

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

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

2018-06-16 Thread glisse at gcc dot gnu.org 
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80335

Marc Glisse  changed:

   What|Removed |Added

 Status|NEW |RESOLVED
 Resolution|--- |FIXED

--- Comment #2 from Marc Glisse  ---
Looks like this is fixed. Although the limitations discussed are present:
optional> copies the whole array even if it is never
engaged.

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

2017-08-31 Thread sgunderson at bigfoot dot com 
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80335

sgunderson at bigfoot dot com changed:

   What|Removed |Added

 CC||sgunderson at bigfoot dot com

--- Comment #1 from sgunderson at bigfoot dot com ---
This also affects the _returning_ std::optional; since it is not trivially copy
constructible, std::optional must be returned (at least on amd64) by means
of a hidden parameter instead of in registers.

Since this affects the return type ABI, it can't be changed easily
after-the-fact, so if possible, it should be fixed before C++17 support becomes
non-experimental.

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

2017-04-06 Thread redi at gcc dot gnu.org 
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80335

Jonathan Wakely  changed:

   What|Removed |Added

 Status|UNCONFIRMED |NEW
   Last reconfirmed||2017-04-06
 Ever confirmed|0   |1