[Bug c++/59659] large zero-initialized std::array compile time excessive

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59659

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |compile-time-hog,
                   |                            |memory-hog,
                   |                            |missed-optimization
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2014-01-07
            Summary|large zero-initialized      |large zero-initialized
                   |std::array of std::atomic   |std::array compile time
                   |compile time excessive      |excessive
     Ever confirmed|0                           |1

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
The frontend generates

  struct array arr;

    struct array arr;
  <<cleanup_point <<< Unknown tree: expr_stmt
  <<cleanup_point <<< Unknown tree: expr_stmt
  arr._M_elems[0] = TARGET_EXPR <D.25804, {.D.23130={._M_i=0}}> >>>>>;
  <<cleanup_point <<< Unknown tree: expr_stmt
  arr._M_elems[1] = TARGET_EXPR <D.25805, {.D.23130={._M_i=0}}> >>>>>;
  <<cleanup_point <<< Unknown tree: expr_stmt
  arr._M_elems[2] = TARGET_EXPR <D.25806, {.D.23130={._M_i=0}}> >>>>>;
  <<cleanup_point <<< Unknown tree: expr_stmt
  arr._M_elems[3] = TARGET_EXPR <D.25807, {.D.23130={._M_i=0}}> >>>>>;
...

instead of generating a loop.  Which may be the cause of std::atomic
having some subtle property (thus reproducible with a random class with
that very same property eventually).

Same issue with the following, so it's std::array's fault (or rather
initializer
list support).

#include <array>

class Foo { public: Foo() {} int i; };

int main() {
    std::array<Foo, 1000000> arr = {{}}; // Halting problem.
}