[Bug fortran/52865] GCC can't vectorize fortran loop but able to vectorize similar c-loop

[jakub at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52865



--- Comment #10 from Jakub Jelinek <jakub at gcc dot gnu.org> 2013-01-16 
10:47:18 UTC ---

BTW, does Fortran have well defined number of iterations if say a do loop goes

from (unknown to compiler):

  integer :: i, m, n

  m = huge(0) - 7

  n = huge(0) - 2

  do i = m, n, 4

   ...

  end do

?  If it must iterate exactly twice (for i = huge(0) - 7 and i = huge(0) - 3),

then it can't be expressed as a corresponding C loop (which would end up with

undefined behavior).  But using a temporary, increment and then test of the

temporary should be doable in the FE, the question is if it does cure this.