[Bug c++/100807] New: initialization of global struct with large array leads to huge assembly

[sbence92 at gmail dot com via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100807

            Bug ID: 100807
           Summary: initialization of global struct with large array leads
                    to huge assembly
           Product: gcc
           Version: 11.1.0
            Status: UNCONFIRMED
          Keywords: compile-time-hog
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: sbence92 at gmail dot com
  Target Milestone: ---
              Host: x86_64-w64-mingw32, x86_64-linux-gnu
            Target: x86_64-w64-mingw32, x86_64-linux-gnu
             Build: x86_64-w64-mingw32, x86_64-linux-gnu

The below is a reduced version of a file that took 33 minutes(!) to compile,
cc1 starting from 1GB of memory usage, reaching 2GB eventually.
This example takes ~12 seconds, ~700 MB of memory and generates 14MB of
assembly as gcc unrolls the constructor calls even with O0 and crashes with O1
and above.

clang and icc is fine, they do this with a loop, msvc kindof the same.
This seems to be and old issue, even gcc 4 timeouts on godbolt.

struct B
{
   B() {}
};

struct A
{

   B b[128][1875];
};

A a{};