[Bug fortran/125864] New: Warn about invalid DO CONCURRENT constructs

[tkoenig at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125864

            Bug ID: 125864
           Summary: Warn about invalid DO CONCURRENT constructs
           Product: gcc
           Version: 17.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: fortran
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tkoenig at gcc dot gnu.org
  Target Milestone: ---

We should warn about invalid constructs in DO CONCURRENT which
violate F2023,

11.1.7.5 Additional semantics for DO CONCURRENT constructs.

[...]

If a variable has unspecified locality

if it is referenced in an iteration it shall either be previously
defined during that iteration, or shall not be defined or become
undefined during any other iteration; if it is defined or becomes
undefined by more than one iteration it becomes undefined when the loop
terminates