[Bug fortran/37749] ICE on array section with vector subscript

["mikael dot morin at tele2 dot fr" <gcc-bugzilla@gcc.gnu.org>]

------- Comment #1 from mikael dot morin at tele2 dot fr  2008-10-29 20:59 -------
Reduced case:

subroutine subr (m, n, a, b, c, d, p)
  implicit none
  integer m, n
  real a(m,n), b(m,n), c(n,n), d(m,n)
  integer p(n)
  d = a(:,p) - matmul(b, c)
end subroutine


The problem is with a(:,p) - matmul(b,c)

It arises because:
(1) gfc_conv_loop_setup chooses matmul's ss to setup the loop bounds. 
    This explains why -matmul(b,c) + a(:,p) works.
(2) The loop->to are asserted to be NULL in gfc_conv_loop_setup
    (GFC_SS_FUNCTION case)
(3) gfc_add_ss_loop_code for the second dimension of a(:,p) calls
    gfc_set_loop_bounds_from_array_spec which sets the second dimension of
    the loop.to
(4) in the loop setting the descriptor in gfc_trans_create_temp_array, 
    in the first iteration, (n = 0), loop.to is NULL, and the size is set to
    NULL. 
(5) In the next iteration, (n = 1), loop.to != NULL, and the loop follows
    the normal path. The size however was set to NULL (condition (4)).


(4) and (5) explain why it works with a(q,:) - matmul(b,c)


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37749