Bug of nvfortran 25.7 with empty arrays

Accelerated Computing HPC Compilers nvc, nvc++ and nvfortran
1

This is yet another bug of nvfortran when handling empty arrays.

Reproducer:

! This program illustrates a bug of nvfortran 25.7-0.
!--------------------------------------------------------------------------------------------------!
! Test 1.
! $ uname -a && nvfortran --version && nvfortran -C -O2 test_bd.f90 && ./a.out
! Linux 6.14.0-27-generic #27~24.04.1-Ubuntu SMP PREEMPT_DYNAMIC Tue Jul 22 17:38:49 UTC 2 x86_64 x86_64 x86_64 GNU/Linux
! nvfortran 25.7-0 64-bit target on x86-64 Linux -tp haswell
! NVIDIA Compilers and Tools
! Copyright (c) 2025, NVIDIA CORPORATION & AFFILIATES.  All rights reserved.
!  A(:, i+1:n) =
! 0: Subscript out of range for array a (test_bd.f90: 34)
!     subscript=3, lower bound=1, upper bound=2, dimension=2
!--------------------------------------------------------------------------------------------------!
! Test 2.
! $ uname -a && nvfortran --version && nvfortran -Mbounds -O2 test_bd.f90 && ./a.out
! Linux zX13 6.14.0-27-generic #27~24.04.1-Ubuntu SMP PREEMPT_DYNAMIC Tue Jul 22 17:38:49 UTC 2 x86_64 x86_64 x86_64 GNU/Linux

! nvfortran 25.7-0 64-bit target on x86-64 Linux -tp haswell
! NVIDIA Compilers and Tools
! Copyright (c) 2025, NVIDIA CORPORATION & AFFILIATES.  All rights reserved.
!  A(:, i+1:n) =
! 0: Subscript out of range for array a (test_bd.f90: 34)
!     subscript=3, lower bound=1, upper bound=2, dimension=2
!--------------------------------------------------------------------------------------------------!

program test_bd
implicit none

integer :: n, i
real :: A(2, 2), Anew(4)
A =  0.0
n = size(A, 2)
i = n
write(*, *) "A(:, i+1:n) = ", A(:, i + 1:n)
Anew = [A(:, 1:i - 1), A(:, i + 1:n), A(:, i)]
write(*, *) "Anew = ", Anew

end program test_bd

Tests:

$ uname -a && nvfortran --version && nvfortran -C -O2 test_bd.f90 && ./a.out
Linux 6.14.0-27-generic #27~24.04.1-Ubuntu SMP PREEMPT_DYNAMIC Tue Jul 22 17:38:49 UTC 2 x86_64 x86_64 x86_64 GNU/Linux

nvfortran 25.7-0 64-bit target on x86-64 Linux -tp haswell 
NVIDIA Compilers and Tools
Copyright (c) 2025, NVIDIA CORPORATION & AFFILIATES.  All rights reserved.
 A(:, i+1:n) = 
0: Subscript out of range for array a (test_bd.f90: 34)
    subscript=3, lower bound=1, upper bound=2, dimension=2

$ uname -a && nvfortran --version && nvfortran -Mbounds -O2 test_bd.f90 && ./a.out
Linux 6.14.0-27-generic #27~24.04.1-Ubuntu SMP PREEMPT_DYNAMIC Tue Jul 22 17:38:49 UTC 2 x86_64 x86_64 x86_64 GNU/Linux

nvfortran 25.7-0 64-bit target on x86-64 Linux -tp haswell 
NVIDIA Compilers and Tools
Copyright (c) 2025, NVIDIA CORPORATION & AFFILIATES.  All rights reserved.
 A(:, i+1:n) = 
0: Subscript out of range for array a (test_bd.f90: 34)
    subscript=3, lower bound=1, upper bound=2, dimension=2

See also test_compiler/test_bd.f90 at master · zequipe/test_compiler · GitHub .

Note:

  1. By the Fortran standards, A(:, n+1 : n) is an empty array.
  2. Related issues:

Thank you for taking a look.

2

Thanks Zaikunzhang, I’ve filed TPR#37701.

Though to set your expectation, Engineering may or may not fix this one. We’re in development of a new Fortran compiler in cooperation with the LLVM community that will eventually replace our current nvfortran. Not that they wont fix this, they do still get fixes in, but given bounds checking is a lower priority feature, they may wait for the new compiler.

-Mat

1 Like
3

Hi Zaikunzhang,

Engineering was able to fix this one, TPR #37701, in our 25.11 release.

-Mat