[Bug c++/86320] very long compilation time for std::array, 1024 * 1024>

[skvadrik at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86320

Ulya <skvadrik at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|very long compilatio n      |very long compilation time
                   |                            |for
                   |                            |std::array<std::pair<int,
                   |                            |int>, 1024 * 1024>

--- Comment #1 from Ulya <skvadrik at gmail dot com> ---
Compilation takes very long time for an array of tuples. Time depends on the
length of an array. Clang doesn't seem to have this problem. 

// 1.cpp
#include <array>
#include <utility>

void foo ()
{
  std::array<std::pair<int, int>, 1024 * 1024> arr {};
}

$ time g++ --std=c++11 -c 1.cpp

real    0m48.344s
user    0m45.545s
sys     0m2.306s

$ time clang++ --std=c++11 -c 1.cpp

real    0m0.540s
user    0m0.322s
sys     0m0.030s

A quick check shows that previous GCC version are affected as well:

https://godbolt.org/g/s3yudL the previous GCC versions 

Finally, this the following program with a user-defined 'pair' type compiles
fast:

#include <array>

template <typename T, typename U>
struct pair
{
  T t;
  U u;
};

void foo ()
{
  std::array<pair<int, int>, 1024 * 1024> arr {};
}

$ time g++ --std=c++11 -c 1.cpp

real    0m0.172s
user    0m0.159s
sys     0m0.011s