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

[Eugene Epshteyn via flang-commits]

eugeneepshteyn wrote:

@mlir-maiden , please check the following:

(1) It seems that in `CharacterizeProcedure()` you may need to tell procedure being characterized that it's SIMPLE procedure. Consider the following:
```
subroutine test(f)
  interface
    simple subroutine f()
    end subroutine
  interface
end subroutine
```
What are the characteristics of `f()`? Do they include `SIMPLE`?

(2) Please check if the following compiles:
```
module test_simple

abstract interface
  simple subroutine simple_proc()
  end subroutine
end interface

contains

subroutine call_it(p)
  procedure(simple_proc) :: p
end subroutine

simple subroutine my_simple()
end subroutine

subroutine test()
  call call_it(my_simple)
end subroutine
end module
```
(3) The following should work, because ABS (and many other intrinsics) are inherently SIMPLE:
```
simple subroutine test()
  real :: x
  x = abs(-1.0)
end subroutine
```
(4) This should fail:
```
simple impure subroutine bug()
end subroutine
```

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