Hello,
I was just looking at the output of the data dep analyzer for
ltrans-1.c and I was quite surprised to see that array indexes are
analyzed twice, as in the following output:
(analyze_array
(ref = u[D.1485_16];
)
(analyze_scalar_evolution
(loop_nb = 1)
(scalar = D.1485_16)
(get_scalar_evolution
(scalar = D.1485_16)
(scalar_evolution = {0, +, 1336}_1))
(set_scalar_evolution
(scalar = D.1485_16)
(scalar_evolution = {0, +, 1336}_1))
)
(instantiate_parameters
(loop_nb = 1)
(chrec = {0, +, 1336}_1)
(res = {0, +, 1336}_1))
)
Here D.1485_16 has an evolution already stored in the cache. However,
just below we get a full recomputation of the same D.1485_16:
(analyze_scalar_evolution
(loop_nb = 1)
(scalar = D.1485_16)
(get_scalar_evolution
(scalar = D.1485_16)
(scalar_evolution = {0, +, 1336}_1))
(analyze_scalar_evolution
(loop_nb = 1)
(scalar = i_3)
(get_scalar_evolution
(scalar = i_3)
(scalar_evolution = {0, +, 1}_1))
(analyze_initial_condition
(loop_phi_node =
i_3 = PHI <i_20(8), 0(5)>;)
(init_cond = 0))
(analyze_evolution_in_loop
(loop_phi_node = i_3 = PHI <i_20(8), 0(5)>;)
(add_to_evolution
(loop_nb = 1)
(chrec_before = 0)
(to_add = 1)
(res = {0, +, 1}_1))
(evolution_function = {0, +, 1}_1))
(set_scalar_evolution
(scalar = i_3)
(scalar_evolution = {0, +, 1}_1))
)
(analyze_scalar_evolution
(loop_nb = 1)
(scalar = 1336)
(get_scalar_evolution
(scalar = 1336)
(scalar_evolution = 1336))
)
(set_scalar_evolution
(scalar = D.1485_16)
(scalar_evolution = {0, +, 1336}_1))
)
The problem seems to be that analyze_offset_expr calls the scev
analyzer explicitely asking for recomputation (third parameter is
true):
/* 2. Variable. Try to substitute with initial_condition of the corresponding
access_fn in the current loop. */
if (SSA_VAR_P (expr))
{
tree access_fn = analyze_scalar_evolution (loop, expr, true,
&unknown_evolution);
Why should we start the analysis from scratch in this case? The same
question could be asked for all the uses of analyze_scalar_evolution
in the vectorizer... Grepping for analyze_scalar_evolution, you get
the following places (in autovect branch) that explicitely ask for
scev recomputation:
tree-vect-analyze.c:551: access_fn = analyze_scalar_evolution (loop, def,
true, &unknown_evolution);
tree-vect-analyze.c:2226: (loop, analyze_scalar_evolution (loop,
PHI_RESULT (phi), true,
tree-vect-transform.c:605: access_fn = analyze_scalar_evolution (loop,
def, true,
tree-vect-transform.c:2548: access_fn = analyze_scalar_evolution (loop,
PHI_RESULT (phi), true,
tree-data-ref.c:940: tree access_fn = analyze_scalar_evolution (loop, ptr_ref,
true,
tree-data-ref.c:1151: tree access_fn = analyze_scalar_evolution (loop,
expr, true,
