[Bug c++/67550] New: Initialization of local struct array with elements of global array yields zeros instead of initializer values

[f.knauf at mmkf dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67550

            Bug ID: 67550
           Summary: Initialization of local struct array with elements of
                    global array yields zeros instead of initializer
                    values
           Product: gcc
           Version: 5.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: f.knauf at mmkf dot de
  Target Milestone: ---

Initializing a function-local struct array from values in a global struct array
yields wrong values with gcc 5.2.1. The problem can be reproduced with the
following code:

    #include <iostream>
    #include <limits>

    struct S {
      int x;
      int y;
    };

    S const data[] = {
      { 1, std::numeric_limits<int>::max() }
    };

    int main() {
      S data2[] = {
        data[0]
      };

      std::cout
        << data [0].x << ", " << data [0].y << "\n"
        << data2[0].x << ", " << data2[0].y << "\n"
        ;
    }

The output is:

    $ g++ -Wall -Wextra -pedantic foo.cc
    $ ./a.out 
    1, 2147483647
    1, 0

The expected output was:

    1, 2147483647
    1, 2147483647

I am using gcc 5.2.1 on Debian sid (Linux 4.1.3) for x86-64. The error is also
reproducible with gcc 5.2.0 on Arch Linux (also x86-64) and gcc 5.1.1 on Fedora
22 (also x86-64). It is not reproducible with gcc 4.9.3.

A workaround for the error is to remove the "const" keyword from the
declaration of "data", i.e.

    S data[] = {
      { 1, std::numeric_limits<int>::max() }
    };

The error also does not appear if std::numeric_limits<int>::max() is replaced
with a compile-time constant value (such as 42). Consequently, in C++11 mode 
(where std::numeric_limits<int>::max() is constexpr) the above code does not
reproduce the error. Instead,

    int foo() { return 23; }

    S const data[] = {
      { 1, foo() }
    };

can be used to produce the wrong result. With

    int constexpr foo() { return 23; }

the correct result is produced.