On 8/14/19 1:37 PM, Jeff Law wrote:
On 8/13/19 6:39 PM, Aldy Hernandez wrote:
On 8/12/19 7:46 PM, Jeff Law wrote:
On 8/12/19 12:43 PM, Aldy Hernandez wrote:
This is a fresh re-post of:
https://gcc.gnu.org/ml/gcc-patches/2019-07/msg00006.html
Andrew gave me some feedback a week ago, and I obviously don't
remember
what it was because I was about to leave on PTO. However, I do
remember
I addressed his concerns before getting drunk on rum in tropical
islands.
FWIW found a great coffee infused rum while in Kauai last week.
I'm not
a coffee fan, but it was wonderful. The one bottle we brought back
isn't going to last until Cauldron and I don't think I can get a
special
order filled before I leave :(
You must bring some to Cauldron before we believe you. :)
That's the problem. The nearest place I can get it is in Vegas and
there's no distributor in Montreal. I can special order it in our
state run stores, but it won't be here in time.
Of course, I don't mind if you don't believe me. More for me in that
case...
Is the supports_type_p stuff there to placate the calls from
ipa-cp? I
can live with it in the short term, but it really feels like there
should be something in the ipa-cp client that avoids this silliness.
I am not happy with this either, but there are various places where
statements that are !stmt_interesting_for_vrp() are still setting a
range of VARYING, which is then being ignored at a later time.
For example, vrp_initialize:
if (!stmt_interesting_for_vrp (phi))
{
tree lhs = PHI_RESULT (phi);
set_def_to_varying (lhs);
prop_set_simulate_again (phi, false);
}
Also in evrp_range_analyzer::record_ranges_from_stmt(), where we if
the
statement is interesting for VRP but extract_range_from_stmt() does
not
produce a useful range, we also set a varying for a range we will
never
use. Similarly for a statement that is not interesting in this hunk.
Ugh. One could perhaps argue that setting any kind of range in these
circumstances is silly. But I suspect it's necessary due to the
optimistic handling of VR_UNDEFINED in value_range_base::union_helper.
It's all coming back to me now...
Then there is vrp_prop::visit_stmt() where we also set VARYING for
types
that VRP will never handle:
case IFN_ADD_OVERFLOW:
case IFN_SUB_OVERFLOW:
case IFN_MUL_OVERFLOW:
case IFN_ATOMIC_COMPARE_EXCHANGE:
/* These internal calls return _Complex integer type,
which VRP does not track, but the immediate uses
thereof might be interesting. */
if (lhs && TREE_CODE (lhs) == SSA_NAME)
{
imm_use_iterator iter;
use_operand_p use_p;
enum ssa_prop_result res = SSA_PROP_VARYING;
set_def_to_varying (lhs);
I've adjusted the patch so that set_def_to_varying will set the
range to
VR_UNDEFINED if !supports_type_p. This is a fail safe, as we can't
really do anything with a nonsensical range. I just don't want to
leave
the range in an indeterminate state.
I think VR_UNDEFINED is unsafe due to value_range_base::union_helper.
And that's a more general than this patch. VR_UNDEFINED is _not_ a
safe
range to set something to if we can't handle it. We have to use
VR_VARYING.
Why? See the beginning of value_range_base::union_helper:
/* VR0 has the resulting range if VR1 is undefined or VR0 is
varying. */
if (vr1->undefined_p ()
|| vr0->varying_p ())
return *vr0;
/* VR1 has the resulting range if VR0 is undefined or VR1 is
varying. */
if (vr0->undefined_p ()
|| vr1->varying_p ())
return *vr1;
This can get called for something like
a = <cond> ? name1 : name2;
If name1 was set to VR_UNDEFINED thinking that VR_UNDEFINED was a safe
value for something we can't handle, then we'll incorrectly return the
range for name2.
I think that if name1 was !supports_type_p, we will have never called
union/intersect. We will have bailed at some point earlier. However, I
do see your point about being consistent.
VR_UNDEFINED can only be used for the ranges of objects we haven't
processed. If we can't produce a range for an object because the
statement is something we don't handle or just doesn't produce anythign
useful, then the right result is VR_VARYING.
This may be worth commenting at the definition site for VR_*.
I also noticed that Andrew's patch was setting num_vr_values to
num_ssa_names + num_ssa_names / 10. I think he meant num_vr_values +
num_vr_values / 10. Please verify the current incantation makes
sense.
Going to assume this will be adjusted per the other messages in this
thread.
Done.
diff --git a/gcc/tree-ssa-threadedge.c b/gcc/tree-ssa-threadedge.c
index 39ea22f0554..663dd6e2398 100644
--- a/gcc/tree-ssa-threadedge.c
+++ b/gcc/tree-ssa-threadedge.c
@@ -182,8 +182,10 @@ record_temporary_equivalences_from_phis (edge e,
new_vr->deep_copy (vr_values->get_value_range (src));
else if (TREE_CODE (src) == INTEGER_CST)
new_vr->set (src);
+ else if (value_range_base::supports_type_p (TREE_TYPE (src)))
+ new_vr->set_varying (TREE_TYPE (src));
else
- new_vr->set_varying ();
+ new_vr->set_undefined ();
So I think this can cause problems. VR_VARYING seems like the right
state here.
+
+ if (!value_range_base::supports_type_p (TREE_TYPE (var)))
+ {
+ vr->set_undefined ();
+ return vr;
Probably better as VR_VARYING here too.
+ {
+ /* If we have an unsupported type (structs, void, etc), there
+ is nothing we'll be able to do with this entry.
+ Initialize it to UNDEFINED as a sanity measure, just in
+ case. */
+ vr->set_undefined ();
Here too.
Hmmm, the problem with setting VR_VARYING for unsupported types is that
we have no min/max to use. Even though min/max will not be used in any
calculation, it's nice to have it set so type() will work consistently.
May I suggest this generic approach while we disassociate the lattice
and ranges from value_range_base (or remove vrp altogether :))?
void
value_range_base::set_varying (tree type)
{
m_kind = VR_VARYING;
if (supports_type_p (type))
{
m_min = vrp_val_min (type, true);
m_max = vrp_val_max (type, true);
}
else
{
/* We can't do anything range-wise with these types. Build
something for which type() will work as a temporary measure
until lattices and value_range_base are disassociated. */
m_min = m_max = build1 (NOP_EXPR, type, void_type_node);
}
}
This way, no changes happen throughout the code, varying remains
varying, type() works everywhere, and we don't have to dig into all
value_range users to skip unsupported types.
This should work, as no one is going to call min() / max() on an
unsupported type, since they're just being used for the lattice.
