int* GetParent(void);
int* FindCommonAncestor(int *aNode1, int *aNode2)
{
if (aNode1 && aNode2) {
int offset = 0;
int *anc1 = aNode1;
for (;;) {
++offset;
int * parent = GetParent();
if (!parent)
break;
anc1 = parent;
}
int *anc2 = aNode2;
for (;;) {
--offset;
int * parent = GetParent();
if (!parent)
break;
anc2 = parent;
}
if (anc1 == anc2) {
anc1 = aNode1;
anc2 = aNode2;
while (offset > 0) {
anc1 = GetParent();
--offset;
}
while (offset < 0) {
anc2 = GetParent();
++offset;
}
while (anc1 != anc2) {
anc1 = GetParent();
anc2 = GetParent();
}
return anc1;
}
}
return 0;
}
Folding predicate offset_5 < 0 to 0
Folded statement: if (offset_5 < 0)
into: if (0)
that is, the second last loop is never executed according to VRP/SCEV because
the exit value of the third last loop
<bb 26>:
offset_48 = ASSERT_EXPR <offset_4, offset_4 <= 0>;
is adjusted to [0, 0] by SCEV:
Visiting statement:
offset_48 = ASSERT_EXPR <offset_4, offset_4 <= 0>;
(analyze_scalar_evolution
(loop_nb = 0)
(scalar = offset_48)
(get_scalar_evolution
(scalar = offset_48)
(scalar_evolution = ))
(analyze_scalar_evolution
(loop_nb = 0)
(scalar = offset_4)
(get_scalar_evolution
(scalar = offset_4)
(scalar_evolution = ))
(analyze_initial_condition
(loop_phi_node =
offset_4 = PHI <offset_37(10), offset_32(9)>)
(init_cond = offset_37))
(analyze_evolution_in_loop
(loop_phi_node = offset_4 = PHI <offset_37(10), offset_32(9)>)
(add_to_evolution
(loop_nb = 3)
(chrec_before = offset_37)
(to_add = -1)
(res = {offset_37, +, -1}_3))
(evolution_function = {offset_37, +, -1}_3))
(set_scalar_evolution
(scalar = offset_4)
(scalar_evolution = {offset_37, +, -1}_3))
(number_of_iterations_in_loop
(analyze_scalar_evolution
(loop_nb = 3)
(scalar = offset_4)
(get_scalar_evolution
(scalar = offset_4)
(scalar_evolution = {offset_37, +, -1}_3))
(set_scalar_evolution
(scalar = offset_4)
(scalar_evolution = {offset_37, +, -1}_3))
)
(analyze_scalar_evolution
(loop_nb = 3)
(scalar = 0)
(get_scalar_evolution
(scalar = 0)
(scalar_evolution = 0))
)
Analyzing # of iterations of loop 3
exit condition 0 < [offset_46, + , -1](no_overflow)
bounds on difference of bases: -2147483648 ... 2147483647
result:
# of iterations (unsigned int) offset_46, bounded by 2147483647
(set_nb_iterations_in_loop = (unsigned int) offset_46))
(chrec_apply
(varying_loop = 3
)
(chrec = {offset_37, +, -1}_3)
(x = offset_46)
(res = offset_37 - offset_46))
(analyze_scalar_evolution
(loop_nb = 0)
(scalar = offset_37)
(get_scalar_evolution
(scalar = offset_37)
(scalar_evolution = ))
(analyze_scalar_evolution
(loop_nb = 0)
(scalar = offset_46)
(get_scalar_evolution
(scalar = offset_46)
(scalar_evolution = ))
(analyze_scalar_evolution
(loop_nb = 0)
(scalar = offset_24)
(get_scalar_evolution
(scalar = offset_24)
(scalar_evolution = {offset_40 + -1, +, -1}_2))
(number_of_iterations_in_loop
(analyze_scalar_evolution
(loop_nb = 2)
(scalar = parent_25)
(get_scalar_evolution
(scalar = parent_25)
(scalar_evolution = parent_25))
(set_scalar_evolution
(scalar = parent_25)
(scalar_evolution = parent_25))
)
(analyze_scalar_evolution
(loop_nb = 2)
(scalar = parent_25)
(get_scalar_evolution
(scalar = parent_25)
(scalar_evolution = parent_25))
(set_scalar_evolution
(scalar = parent_25)
(scalar_evolution = parent_25))
)
(set_nb_iterations_in_loop = scev_not_known))
)
(set_scalar_evolution
(scalar = offset_46)
(scalar_evolution = offset_24))
)
(set_scalar_evolution
(scalar = offset_37)
(scalar_evolution = offset_24))
)
(analyze_scalar_evolution
(loop_nb = 0)
(scalar = offset_46)
(get_scalar_evolution
(scalar = offset_46)
(scalar_evolution = offset_24))
(set_scalar_evolution
(scalar = offset_46)
(scalar_evolution = offset_24))
)
)
(set_scalar_evolution
(scalar = offset_48)
(scalar_evolution = 0))
)
(instantiate_parameters
(loop_nb = 0)
(chrec = 0)
(res = 0))
Found new range for offset_48: [0, 0]
where the particular error looks like this:
Analyzing # of iterations of loop 3
exit condition 0 < [offset_46, + , -1](no_overflow)
bounds on difference of bases: -2147483648 ... 2147483647
result:
# of iterations (unsigned int) offset_46, bounded by 2147483647
(set_nb_iterations_in_loop = (unsigned int) offset_46))
as it may be zero, in case offset_46 is <= 0.
Sebastian, Zdenek - any idea what goes wrong here?
--
Summary: [4.3 Regression] VRP/SCEV miscompiles Firefox
Product: gcc
Version: 4.3.0
Status: UNCONFIRMED
Keywords: wrong-code
Severity: normal
Priority: P3
Component: tree-optimization
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: rguenth at gcc dot gnu dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34244
