[Bug c++/77397] New: function initializing global static variables not optimized again fully

["noone at turm-lahnstein dot de" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77397

            Bug ID: 77397
           Summary: function initializing global static variables not
                    optimized again fully
           Product: gcc
           Version: 6.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: noone@turm-lahnstein.de
  Target Milestone: ---

Compiling 

static int data = 0;  static int dummy = data; int main() { }

with g++ -Os leads to a less than perfect assembler code:

        .file   "main.cpp"
        .section        .text.startup,"ax",@progbits
        .globl  main
        .type   main, @function
main:
.LFB0:
        .cfi_startproc
        xorl    %eax, %eax
        ret
        .cfi_endproc
.LFE0:
        .size   main, .-main
        .type   _GLOBAL__sub_I_main, @function
_GLOBAL__sub_I_main:
.LFB2:
        .cfi_startproc
        ret
        .cfi_endproc
.LFE2:
        .size   _GLOBAL__sub_I_main, .-_GLOBAL__sub_I_main
        .ident  "GCC: (GNU) 6.1.0"
        .section        .note.GNU-stack,"",@progbits


Because the static variables are optimized away, __GLOBAL__sub_I_main (used to
initialize them in the versions prior to 5.0) is not needed at all.

This carelessness is a likely cause for bug 77396.