[Bug fortran/78178] New: ICE in WHERE statement with diagnostic

["tkoenig at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78178

            Bug ID: 78178
           Summary: ICE in WHERE statement with diagnostic
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tkoenig at gcc dot gnu.org
  Target Milestone: ---

This is a spin-off from PR 65944.

As noted by Dominique in https://gcc.gnu.org/ml/fortran/2016-11/msg00002.html ,
gfc_match_simple_where also has an issue with not setting the locus
correctly.  Test case:

! { dg-do compile }
! { dg-options "-Wcharacter-truncation" }
subroutine where_ice (i,j)

  implicit none

  character(8)  :: y(10,10,2)

  integer       :: i
  integer       :: j

  character(12) :: txt(5)
  if (.true.) where (txt(1:3) /= ''   )  y(1:3,i,j) = txt(1:3) ! { dg-warning
"CHARACTER expression will be truncated" }

end subroutine where_ice

Problem is that the obvious and simple fix

Index: match.c
===================================================================
--- match.c     (Revision 241745)
+++ match.c     (Arbeitskopie)
@@ -6219,6 +6219,7 @@ match_simple_where (void)

   c->next = XCNEW (gfc_code);
   *c->next = new_st;
+  c->next->loc = gfc_current_locus;
   gfc_clear_new_st ();

   new_st.op = EXEC_WHERE;

leads to lots of regressions:

ig25@linux-fd1f:~/Krempel/Where> gfortran actual_array_offset_1.f90 
f951: internal compiler error: Segmentation fault
0xc2695f crash_signal
        ../../trunk/gcc/toplev.c:338
0x6f0ba6 resolve_select_type
        ../../trunk/gcc/fortran/resolve.c:8768
0x6e719c gfc_resolve_code(gfc_code*, gfc_namespace*)
        ../../trunk/gcc/fortran/resolve.c:11045
0x6e94a7 resolve_codes
        ../../trunk/gcc/fortran/resolve.c:16025
0x6e93ee resolve_codes
        ../../trunk/gcc/fortran/resolve.c:16010
0x6e956e gfc_resolve(gfc_namespace*)
        ../../trunk/gcc/fortran/resolve.c:16060
0x6d3ff2 gfc_parse_file()
        ../../trunk/gcc/fortran/parse.c:6092
0x717902 gfc_be_parse_file
        ../../trunk/gcc/fortran/f95-lang.c:198
Please submit a full bug report,
with preprocessed source if appropriate.
Please include the complete backtrace with any bug report.
See <http://gcc.gnu.org/bugs.html> for instructions.

What on earth is going on there I don't know.  I think I will
build from a clean tree and retry, and in the meantime fix
PR 65944 on the other branches.