On 8/15/19 10:06 AM, Aldy Hernandez wrote: > > > On 8/15/19 7:23 AM, Richard Biener wrote: >> On Thu, Aug 15, 2019 at 12:40 PM Aldy Hernandez <al...@redhat.com> wrote: >>> >>> 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. >> >> Then use error_mark_node or NULL_TREE?! > > I tested with error_mark_node. It seems no one is calling type() on > these unsupported types, so perhaps error_mark_node is fine, and signals > that we don't support these types if anyone tries to do anything funny > with them. I've adjusted the patch. I like error_mark_node. It makes it pretty clear that something has gone horribly wrong as opposed to something perhaps being uninitialized.
jeff
