Bug in nested WHERE construct

[Harald]

Hello,

the following code shows an issue with nested WHERE constructs, which may lead to an unexpected floating point exception:

program nested_where
  implicit none
  integer, parameter :: n = 100
  real               :: x(n), y(n)
  real               :: z = log (0.5)
  call random_number (x)
  y = 1                   ! "Good initialization"
  y = 0                   ! "Bad  initialization"
  print *, count (x == 1) ! Prints 0
  where (x > 0.5)
     y = x
     where (log (y) > z)  ! The "dangerous mask"
        x = 1
     end where
  end where
  print *, count (x == 1) ! Not reached for y=0
end program nested_where

%  ifort -g -traceback nested-where.f90 -fpe0 && ./a.out
           0
forrtl: error (73): floating divide by zero
Image              PC        Routine            Line        Source             
a.out              080A551C  Unknown               Unknown  Unknown
a.out              0804A396  MAIN__                     11  nested-where.f90
a.out              0804A0B6  Unknown               Unknown  Unknown

I had a discussion at

https://groups.google.com/forum/#!topic/comp.lang.fortran/EG2k49ujggA

which appears to support the idea that a standard-conforming compiler should mask the bad values before evaluation of the inner mask.

Or am I missing something?

[Steven_L_Intel1]

I know that in some other contexts (such as MERGE) the mask defines the assignment, not the evaluation, but WHERE may indeed be different. We will investigate.