------- Comment #11 from spop at gcc dot gnu dot org 2010-05-25 23:33 ------- This is not a IV type problem: the number of iterations may be zero when mid == 0 or mid == n, so the number of iterations analysis has a condition under which niter may_be_zero.
I sent out a patch that makes niter return a COND_EXPR instead of a chrec_dont_know: http://gcc.gnu.org/ml/gcc-patches/2010-05/msg01927.html With that patch I now get note: not vectorized: data ref analysis failed D.2726_51 = a[var.9_55]; -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43423
