------- Comment #6 from ian at airs dot com 2007-04-11 07:15 -------
When we pick a new range to avoid an infinite iteration, we have to pick an
overflow range. This is what catches overflows like
for (i = 1; i > 0; ++i) ++bits;
I've experimented with only doing this in a loop, but it didn't work reliably.
Note that we don't throw away all infinities here, we just throw away
[-INF,+INF]. This is code from before the overflow checks were added.
The suggestion of all_but_one_const sounds reasonable to me. What do you think
of this patch?
Index: tree-vrp.c
===================================================================
--- tree-vrp.c (revision 123521)
+++ tree-vrp.c (working copy)
@@ -5059,7 +5059,7 @@ vrp_visit_phi_node (tree phi)
tree lhs = PHI_RESULT (phi);
value_range_t *lhs_vr = get_value_range (lhs);
value_range_t vr_result = { VR_UNDEFINED, NULL_TREE, NULL_TREE, NULL };
- bool all_const = true;
+ int variable_count;
copy_value_range (&vr_result, lhs_vr);
@@ -5069,6 +5069,7 @@ vrp_visit_phi_node (tree phi)
print_generic_expr (dump_file, phi, dump_flags);
}
+ variable_count = 0;
for (i = 0; i < PHI_NUM_ARGS (phi); i++)
{
edge e = PHI_ARG_EDGE (phi, i);
@@ -5089,7 +5090,7 @@ vrp_visit_phi_node (tree phi)
if (TREE_CODE (arg) == SSA_NAME)
{
vr_arg = *(get_value_range (arg));
- all_const = false;
+ ++variable_count;
}
else
{
@@ -5122,7 +5123,7 @@ vrp_visit_phi_node (tree phi)
when the new value is slightly bigger or smaller than the
previous one. */
if (lhs_vr->type == VR_RANGE && vr_result.type == VR_RANGE
- && !all_const)
+ && variable_count > 1)
{
if (!POINTER_TYPE_P (TREE_TYPE (lhs)))
{
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31522
