[flang] invalid code for where

[MarDiehl]

I've encountered an issue with Flang 21.1.5 which generates invalid code for where. I could reproduce something similar with the following snippet. It should print the sequence of numbers from 1 to 33 but it prints 33 33 33 33 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33. Note that I've disabled use of the random number generator because it always gives 2.2470951E-05.

The same behavior is seen on compiler explorer which uses Flang trunk (commit cce852f)

program test

  implicit none
  integer, dimension(:), allocatable :: v
  real :: r
  integer :: i

  call random_number(r) ! does not work

  print*, 'r',r
  r = 0.32
  allocate(v(1+int(r*100.0)),source=0)

  print*, 'size(v)',size(v)

  do i = 1, size(v)
    where(x(size(v),i)) v=i
  end do

  print*, v
  contains

  function x(n,i)
    integer, intent(in) :: n,i
    logical, dimension(:), allocatable :: x

    allocate(x(n),source=.false.)
    x(i) = .true.

  end function x

end program test

Note: Also reported on LLVM Discourse