topic Re: Re:Wrong code (missing temporary) passing array section to explicit size dummy in Intel® Fortran Compiler

Wrong code (missing temporary) passing array section to explicit size dummy

Harald1 — Tue, 07 Mar 2023 21:40:25 GMT

Hello,

the following code prints wrong results in the called subroutine:

module m implicit none contains subroutine s(a, n) integer, intent(in) :: n class(*), intent(in) :: a(n) select type(a) type is(integer) print *,'a is integer, a=', a class default print *,'a is unsupported type' stop 1 end select end end program p use m implicit none integer :: b(2,2) = reshape([21, 22, 23, 24], [2,2]) print *,b call s (b,4) ! OK print * print *,b(:,1::2) call s (b(:,1::2),2) ! OK print * print *,b(1::2,:) call s (b(1::2,:),2) ! bad print * print *,b(2::2,:) call s (b(2::2,:),2) ! bad end

I get with current ifort:

21 22 23 24 a is integer, a= 21 22 23 24 21 22 a is integer, a= 21 22 21 23 a is integer, a= 21 22 22 24 a is integer, a= 22 23

So while the first two cases are ok, the last two are not. Maybe there is no temporary generated for the passed array section to the explicit size dummy, and the actual stride of dimension 1 is not unity.

Thanks,

Harald

Re:Wrong code (missing temporary) passing array section to explicit size dummy

Barbara_P_Intel — Wed, 08 Mar 2023 22:18:18 GMT

Thank you! Love these nice reproducers!

I'll check this out.

Re:Wrong code (missing temporary) passing array section to explicit size dummy

Barbara_P_Intel — Thu, 09 Mar 2023 16:40:43 GMT

I filed a bug, CMPLRLLVM-45596. This reproducer gets the same wrong results with ifx.

Re:Wrong code (missing temporary) passing array section to explicit size dummy

Barbara_P_Intel — Thu, 09 Mar 2023 17:56:10 GMT

UPDATE... the compiler should actually print an error message.

Intel's resident Fortran standards guru told me:

The problem with the test case is that they are passing a two dimensional array section to a one dimensional explicit shape array. This is wrong because 1) passing an array section requires the dummy argument be assumed shape or deferred shape (bounds are declared with colons), and 2) because they are passing a two dimensional array to a one dimensional array and the interface is explicit.

If at line 6, the dimensions of a are declared as “a(:, :)”, it compiles fine an produces the output.

Re: Wrong code (missing temporary) passing array section to explicit size dummy

Harald1 — Thu, 09 Mar 2023 18:28:40 GMT

Would the resident Fortran standard guru please explain this?

For dummy arguments of intrisinc types, this works by F2018: 15.5.2.11 Sequence association. I do not see a reason for this to not apply here, so any helpful pointer is appreciated.

Re: Wrong code (missing temporary) passing array section to explicit size dummy

Harald1 — Thu, 09 Mar 2023 19:04:55 GMT

Here's an extended version that allows comparison of intrinsic type dummy and class(*) dummy:

module m implicit none contains subroutine s(a, n) integer, intent(in) :: n class(*), intent(in) :: a(n) select type(a) type is(integer) print *,'a is integer, a=', a class default print *,'a is unsupported type' stop 1 end select end subroutine t(a, n) integer, intent(in) :: n integer, intent(in) :: a(n) print *,'subroutine t: a=', a end end program p use m implicit none integer :: b(2,2) = reshape([21, 22, 23, 24], [2,2]) print *,b call s (b,4) ! OK call t (b,4) ! OK print * print *,b(:,1::2) call s (b(:,1::2),2) ! OK call t (b(:,1::2),2) ! OK print * print *,b(1::2,:) call s (b(1::2,:),2) ! bad call t (b(1::2,:),2) ! OK print * print *,b(2::2,:) call s (b(2::2,:),2) ! bad call t (b(2::2,:),2) ! OK print * print *, "With an explicit temporary:" call s ((b(2::2,:)),2) ! this is now OK! call t ((b(2::2,:)),2) ! also OK end

So for the subroutine t with a dummy with explicit-shape array of type integer I get what I expect. With class(*) I'd need an explicit temporary.

Re: Wrong code (missing temporary) passing array section to explicit size dummy

Steve_Lionel — Fri, 10 Mar 2023 16:46:00 GMT

I'm afraid that I'm on Harald's side here - there is no requirement that the dummy argument be assumed-shape. Sequence association does apply.

F2018 15.5.2.4

p18 Except when a procedure reference is elemental (15.8), each element of an array actual argument or of a sequence in a sequence association (15.5.2.11) is associated with the element of the dummy array that has the same position in array element order (9.5.3.2).

The compiler would have to do copy-in (and copy-out if not INTENT(IN) or a vector subscript.)

Re:Wrong code (missing temporary) passing array section to explicit size dummy

Barbara_P_Intel — Fri, 10 Mar 2023 15:54:08 GMT

After more research and discussion behind the scenes, the Fortran gurus determined that the original reproducer is valid code and Intel Fortran has a bug. Bug is filed as a runtime issue.

Re: Re:Wrong code (missing temporary) passing array section to explicit size dummy

FortranFan — Fri, 10 Mar 2023 18:39:45 GMT

@Barbara_P_Intel ,

It is not convincing this is a run-time issue only. The evidence is this is a combination issue with the compile-time actions toward the handling of unlimited polymorphic type with the explicit shape received argument. Because if you try with an integer type as opposed to unlimited polymorphic, you will see the program response is as expected by OP:

module m contains subroutine s(a, n) integer, intent(in) :: n integer, intent(in) :: a(n) print *,'a is integer, a=', a end end

You many want to review this with the Intel Fortran team.

Re:Wrong code (missing temporary) passing array section to explicit size dummy

Barbara_P_Intel — Fri, 10 Mar 2023 19:57:42 GMT

@FortranFan, when I said "runtime issue" I meant that the compiler need not print an error message since the code is legal Fortran.

The compiler is indeed generating bad code for this case. That's the bug.

Re:Wrong code (missing temporary) passing array section to explicit size dummy

Barbara_P_Intel — Tue, 21 Nov 2023 20:30:31 GMT

With the release of 2024.0, both ifx and ifort are printing the correct answers at runtime.

Please check out the new releases.

Re: Wrong code (missing temporary) passing array section to explicit size dummy

Harald1 — Wed, 22 Nov 2023 21:20:59 GMT

The testcase is fixed, indeed!

Thanks!