PR fortran/31243
* resolve.c (resolve_substring): Don't allow too large substring
indexes.
(gfc_resolve_substring_charlen): Fix typo.
(gfc_resolve_character_operator): Fix typo.
(resolve_charlen): Catch unreasonably large string lengths.
* simplify.c (gfc_simplify_len): Don't error out on LEN
range checks.
* gcc/testsuite/gfortran.dg/string_1.f90: New test.
* gcc/testsuite/gfortran.dg/string_2.f90: New test.
* gcc/testsuite/gfortran.dg/string_3.f90: New test.
git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@147619 138bc75d-0d04-0410-961f-82ee72b054a4