Flang semantic error depending on definition order of size/dimension arguments

[hansec]

Hello,

Flang (20.1.5) currently fails in some cases where the size of an argument, which is also passed as an argument itself, is defined after it’s first use. For example, the following simple test case

MODULE test_mod
IMPLICIT NONE
CONTAINS
SUBROUTINE test_sub(a,n)
INTEGER(4), INTENT(in) :: a(n)
INTEGER(8), INTENT(in) :: n
END SUBROUTINE test_sub
END MODULE test_mod

results in the error

./test.F90:6:27: error: The type of 'n' has already been implicitly declared
  INTEGER(8), INTENT(in) :: n
                            ^
./test.F90:4:23: Implicit declaration of 'n'
  SUBROUTINE test_sub(a,n)
                        ^

Note that while the error points to the subroutine definition the actual error appears to be caused by implicit definition of n in the declaration of a. Indeed, if n is defined before a or if n is of default integer type (4 bytes in this case) the error is not thrown.

To be explicit both of the following work

INTEGER(4), INTENT(in) :: a(n)
INTEGER, INTENT(in) :: n

INTEGER(8), INTENT(in) :: n
INTEGER(4), INTENT(in) :: a(n)

I am not sure if this is Flang being pedantic or not, but every other Fortran compiler I work with (Intel, GCC, Cray) supports this ordering of code so it would be nice to not have to change things just to support Flang. This seems somewhat related to #106021.

I tried to look around to see if this was reported earlier but couldn’t find anything. So apologies if this is a repeat. Thanks!

[llvmbot]

@llvm/issue-subscribers-flang-frontend

Author: Chris Hansen (hansec)

Hello,

Flang (20.1.5) currently fails in some cases where a size argument, that is also an argument itself is defined after it’s first use. For example, the following simple test case

MODULE test_mod
IMPLICIT NONE
CONTAINS
SUBROUTINE test_sub(a,n)
INTEGER(4), INTENT(in) :: a(n)
INTEGER(8), INTENT(in) :: n
END SUBROUTINE test_sub
END MODULE test_mod

results in the error

./test.F90:6:27: error: The type of 'n' has already been implicitly declared
  INTEGER(8), INTENT(in) :: n
                            ^
./test.F90:4:23: Implicit declaration of 'n'
  SUBROUTINE test_sub(a,n)
                        ^

Note that while the error points to the subroutine definition the actual error appears to be caused by implicit definition of n in the declaration of a. Indeed, if n is defined before a or if n is of default integer type (4 bytes in this case) the error is not thrown.

To be explicit both of the following work

INTEGER(4), INTENT(in) :: a(n)
INTEGER, INTENT(in) :: n

INTEGER(8), INTENT(in) :: n
INTEGER(4), INTENT(in) :: a(n)

I am not sure if this is Flang being pedantic or not, but every other Fortran compiler I work with (Intel, GCC, Cray) supports this ordering of code so it would be nice to not have to change things just to support Flang. This seems somewhat related to #106021.

I tried to look around to see if this was reported earlier but couldn’t find anything. So apologies if this is a repeat. Thanks!