[flang-dev] Passing intent(in) to the midend

[Alexey Zhikhartsev via flang-dev]

Consider the following code:

    integer :: arr1(42), arr2(42) ! global

    ...

    recursive subroutine foo(a)

    integer, intent(in) :: a


    ! first load of "a" here

    if (a > 20) then

      return

    endif


    arr1(0) = a

    call foo(a + 1)

    arr2(0) = a ! <- redundant load here

    end subroutine foo



As per the Fortran 90 standard [1], `intent(in)` for variable `a`
"specifies that the dummy argument must not be redefined or become
undefined during the execution of the procedure". Thus, we can assume that
the call to `foo()` does not modify `a`, so the redundant load can be
safely removed (e.g., by the GVN pass in the midend).

How can we pass the intent(in) information to the midend so we could take
advantage of it?

[1] The Fortran 90 standard, section 5.1.2.3
https://wg5-fortran.org/N001-N1100/N692.pdf

Best,

Alexey
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