[Bug fortran/79929] New: [7 Regression] Bogus Warning: '__builtin_memset': specified size 4294967291 exceeds maximum object size 2147483647

[anlauf at gmx dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79929

            Bug ID: 79929
           Summary: [7 Regression] Bogus Warning: '__builtin_memset':
                    specified size 4294967291 exceeds maximum object size
                    2147483647
           Product: gcc
           Version: 7.0.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: anlauf at gmx dot de
  Target Milestone: ---

Hi all,

for trunk rev.245718, GNU Fortran (GCC) 7.0.1 20170224 (experimental),
the code:

% cat gfcbug138.f90
subroutine gfcbug138 (yerrmsg)
  character(*) :: yerrmsg
  yerrmsg = ""
  yerrmsg = "bug: " // yerrmsg
end subroutine gfcbug138

produces

% gfc-trunk -Wall -c gfcbug138.f90 -O1
gfcbug138.f90:4:0:

   yerrmsg = "bug: " // yerrmsg

Warning: '__builtin_memset': specified size 4294967291 exceeds maximum object
size 2147483647 [-Wstringop-overflow=]

at -O1, -O2, -O3, but not at -O0.