[Bug tree-optimization/101923] std::function's move ctor is slower than the copy one for empty source objects

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101923

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |missed-optimization
          Component|libstdc++                   |tree-optimization

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Hmm

  __tmp = MEM[(union _Any_data & {ref-all})&f];
  MEM[(union _Any_data * {ref-all})&f] = MEM[(union _Any_data &
{ref-all})&moved];
  MEM[(union _Any_data * {ref-all})&moved] = __tmp;
  __tmp ={v} {CLOBBER};
  _13 = MEM[(void (*type) (const union _Any_data & {ref-all}, const struct Car
&) &)&f + 24];
  _14 = MEM[(void (*type) (const union _Any_data & {ref-all}, const struct Car
&) &)&moved + 24];
  MEM[(void (*<Te9f8>) (const union _Any_data & {ref-all}, const struct Car &)
&)&f + 24] = _14;
  MEM[(void (*<Te9f8>) (const union _Any_data & {ref-all}, const struct Car &)
&)&moved + 24] = _13;

So a missed optimization at the gimple level.
But note the arm64 compiler on godbolt is a few months old, 20210528.  There
might have been some fixes which improve this already.