maxloc oddity with Intel 15+

All,

I'm currently trying to port a code that works on Intel 15 to use Intel 16 (and 17). In doing so, I encountered a difference in behavior of Intel 16 and 17 compared to 15 (as well as to NAG, PGI, and GNU). A variant also showed a possible bug in Intel 15.

The code is:

program test

   implicit none

   integer, parameter :: nvars = 12
   character(len=*), parameter :: vars(nvars)=(/ &' dw', ' ps', ' pw', ' rw',  &'  q', 'spd', '  t', ' uv',  &'sst', 'gps', 'lag', 'tcp' /)
   integer :: ivars(nvars)
   logical :: lvars(nvars)
   integer :: i
   character(len=3) :: var
   integer :: is(1)

   integer :: iis

   is = 0
   iis = 0

   do i=1,nvars
      ivars(i) = i
   end do

   var = 'X'

   write (*,*) 'var: ', var
   write (*,*) 'vars: ', vars
   write (*,*) 'ivars: ', ivars
   write (*,*) 'vars==var: ', vars==var

   is = maxloc(ivars,vars==var)
   write (*,*) 'is: ', is

   lvars = vars==var
   write (*,*) 'lvars: ', lvars

   iis = maxloc(ivars,dim=1,mask=lvars)
   write (*,*) 'iis: ', iis

end program test

What we are trying to do is find where "var" is in "vars". Now, is maxloc the way to do this? No, probably not, but, still, before I workaround, I want to report this. In this case, since 'X' is not in vars, is -> 0. I've also added a new chunk of code using MAXLOC(ARRAY,DIM=DIM,MASK=MASK) thinking maybe that would help.

Now in Intel 15:

(1513) $ ifort --version
ifort (IFORT) 15.0.2 20150121
Copyright (C) 1985-2015 Intel Corporation.  All rights reserved.

(1514) $ ifort test.F90 && ./a.out
 var: X
 vars:  dw ps pw rw  qspd  t uvsstgpslagtcp
 ivars:            1           2           3           4           5           6
           7           8           9          10          11          12
 vars==var:  F F F F F F F F F F F F
 is:            0
 lvars:  F F F F F F F F F F F F
 iis:            1

Note, is=0 which is why the larger code this is part of worked. My 'dimmed' attempt to see if using dim=1 and outputting an integer threw a 1, which is unexpected.

Now Intel 16:

(1362) $ ifort --version
ifort (IFORT) 16.0.2 20160204
Copyright (C) 1985-2016 Intel Corporation.  All rights reserved.

(1363) $ ifort test.F90 && ./a.out
 var: X
 vars:  dw ps pw rw  qspd  t uvsstgpslagtcp
 ivars:            1           2           3           4           5           6
           7           8           9          10          11          12
 vars==var:  F F F F F F F F F F F F
 is:            1
 lvars:  F F F F F F F F F F F F
 iis:            1

Now is=1. My reading of the standard seems that this use of MAXLOC falls under Case (ii) of the MAXLOC spec:

...If ARRAY has size zero or every element of MASK has the value false, all elements of the result are zero.

Every element of MASK is false is both MAXLOC calls so I think the result should be 0.

Thanks,

Matt