[Bug libstdc++/60621] std::vector::emplace_back generates massively more code than push_back

[marc at kdab dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60621

--- Comment #7 from marc at kdab dot com ---
Retesting with GCC 6.1, it looks better now:

  $ g++ -O2 -o emplace-vs-push_back{.pb,.cpp}
  $ g++ -O2 -o emplace-vs-push_back{.eb,.cpp} -DEMPLACE_BACK
  $ strip emplace-vs-push_back.*
  $ size emplace-vs-push_back.*
   text    data     bss     dec     hex filename
   4474     680       8    5162    142a emplace-vs-push_back.eb
   4830     680       8    5518    158e emplace-vs-push_back.nt
   5083     656       8    5747    1673 emplace-vs-push_back.pb

somewhat at the expense of pessimising push_back(), which used to be 500b
smaller in Comment 3, but at least the relation between emplace_back and
push_back, and between emplace_back(char[2], char[2], char[2]) and
emplace_back(std::string, std::string, std::string) are now as expected.