[Bug tree-optimization/78180] Poor optimization of std::array on gcc 4.8/5.4/6.2 as compared to simple raw array

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78180

--- Comment #7 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
By moving the array to be end of struct Rolling, GCC does the correct thing and
optimizing out the load of idx out of the loop.

That is:

template <class C> class Rolling {
  uint32_t idx_;
  const uint32_t size_;
  C times_{};



----- CUT-----------

Basically:
  MEM[(value_type &)&r][_54] = _2;


Is not treated as referencing the array field but rather referencing the whole
struct so SRA thinks it cannot do anything with it.