------- Comment #6 from rguenth at gcc dot gnu dot org 2008-09-02 09:04 -------
It looks like SCEV does not see that for
(number_of_iterations_in_loop
(analyze_scalar_evolution
(loop_nb = 4)
(scalar = j_3)
(get_scalar_evolution
(scalar = j_3)
(scalar_evolution = ))
(analyze_initial_condition
(loop_phi_node =
j_3 = PHI <j_26(4), j_31(7)>
)
(init_cond = j_26))
(analyze_evolution_in_loop
(loop_phi_node = j_3 = PHI <j_26(4), j_31(7)>
)
(add_to_evolution
(loop_nb = 4)
(chrec_before = j_26)
(to_add = 1)
(res = {j_26, +, 1}_4))
(evolution_function = {j_26, +, 1}_4))
(set_scalar_evolution
(scalar = j_3)
(scalar_evolution = {j_26, +, 1}_4))
)
j_26 is defined by
<bb 4>:
# j_26 = PHI <0(3), 0(5), 0(12), 0(6)>
so it is all zeros. This is because the "iterative" unrolling only does
a cfg cleanup between iterations and not a full constant-prop.
We can "fix" this special case in analyze_initial_condition, but a real
fix would be to run a (partial) CCP pass after each set of unrolling.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37221
