[flang-commits] [flang] [Flang] Add parsing and attribute registration for SIMPLE specifier (PR #161285)

[Eugene Epshteyn via flang-commits]

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eugeneepshteyn wrote:

Please follow `DEREF` pattern in `IsExplicitlyImpureProcedure()`.

Consider the following:
```
module m
  contains
    simple subroutine s()
    end subroutine
end module

program p
  use m
  ! IsSimpleProcedure on the use-assoc symbol for 's' must return true
end program
```
Please double-check this and add a test for this case.

https://github.com/llvm/llvm-project/pull/161285