improve broadcast resolution (#1792)

torch/csrc/jit/codegen/cuda/lower_alias_memory.cpp

@@ -21,43 +21,79 @@ namespace {
 
 //! Checks that the current loop nest is not realizing a serial
 //! broadcast so that each index of producer buffer will only
-//! be visited once.
-//! TODO: should refactor this utility now to use loop maps in a
-//! follow up.
+//! be visited once, which is the only case where aggressive
+//!  inner sharing is valid.
+//!
 bool isSerialBroadcastResolution(TensorView* producer, TensorView* consumer) {
- auto producer_root =
- TensorDomain::noReductions(producer->getMaybeRFactorDomain());
- auto consumer_root =
- TensorDomain::noReductions(consumer->getMaybeRFactorDomain());
-
- if (producer_root.size() != consumer_root.size()) {
- // This case would be a single broadcast or a single reduce
- // which wouldn't be a broadcast resolution
- return false;
+ //! Note: see issue #1785:
+ //! serial broadcast resolution doesn't only happen to
+ //! immediate producers of broadcast ops. We can also have
+ //! example:
+ //! T1[I,B] = broadcast(T0[I]])
+ //! T3[I,I] = T1[I,B] + T2[I,I]
+ //! T4[I,I] = T3[I,I]
+ //! and generates the following loop:
+ //! alloc T0[4]
+ //! For i in 0..3
+ //! T0[...] =
+ //!
+ //! For j in 0...X:
+ //! alloc T3[4]
+ //! for k in 0..3:
+ //! alloc T1[1]
+ //! T1[0] = T0[k] // <- This is actually a broadcast resolution
+ //! T3[k] = T1[0] + T2[...]
+ //! T4[...] = T3[...]
+ //!
+ //! In this case we are actually visiting each pixel of T0 in each iteration
+ //! of the j loop while T1 was the broadcasted tensor causing this reuse.
+ //!
+ //! The current version of checking covers this scenario by checking the root
+ //! ids of the consumer concrete loop id's. Any time a local tensor like T0
+ //! appears in a re-use scenario like above, we should see a serial loop id
+ //! that was derived from some root id that doesn't concretely map to T0's
+ //! domain.
+
+ // Serial concrete loop id's that cover consumer's iter domain.
+ std::vector<Val*> consumer_serial_loop_concrete_ids;
+
+ for (auto consumer_leaf_id : consumer->domain()->domain()) {
+ auto concrete_loop_id = GpuLower::current()->caMap()->getConcreteMappedID(
+ consumer_leaf_id, IdMappingMode::LOOP);
+
+ // Check for any serial loop id with non-trivial extent
+ if (!concrete_loop_id->isThread() &&
+ !concrete_loop_id->extent()->isOneInt()) {
+ consumer_serial_loop_concrete_ids.push_back(concrete_loop_id);
+ }
  }
 
- std::vector<Val*> serial_ids;
- std::copy_if(
- producer->domain()->domain().begin(),
- producer->domain()->domain().end(),
- std::back_inserter(serial_ids),
- [](IterDomain* id) { return !id->isThread(); });
-
- auto serial_producer_roots =
- InputsOf::outputs(FusionGuard::getCurFusion(), serial_ids);
- auto serial_root_id =
- ir_utils::filterByType<IterDomain>(serial_producer_roots);
- std::unordered_set<IterDomain*> serial_producer_root_set(
- serial_root_id.begin(), serial_root_id.end());
-
- for (const auto idx : c10::irange(producer_root.size())) {
- if (producer_root[idx]->isBroadcast() &&
- !consumer_root[idx]->isBroadcast()) {
- // Check if this broadcast contributed to any serial
- // scheduled iterdomains:
- if (serial_producer_root_set.count(producer_root[idx])) {
- return true;
- }
+ // Collect the root id's that the serial loop iterdomain
+ // are transformed from.
+ auto serial_loop_roots = InputsOf::outputs(
+ FusionGuard::getCurFusion(), consumer_serial_loop_concrete_ids);
+
+ // Collect exact concrete id's in producer's root domain
+ std::unordered_set<IterDomain*> producer_exact_concrete_root_ids;
+ auto producer_root =
+ TensorDomain::noReductions(producer->getMaybeRFactorDomain());
+ std::transform(
+ producer_root.begin(),
+ producer_root.end(),
+ std::inserter(
+ producer_exact_concrete_root_ids,
+ producer_exact_concrete_root_ids.begin()),
+ ir_utils::caMapExactConcreteId);
+
+ // Check if serial loop roots indexes any exact root id's that
+ // is not within the set of producer's root exact id's. These
+ // id's will imply that the same producer pixel is accessed
+ // in multiple iterations of the materialized serial loop.
+ for (auto serial_loop_root :
+ ir_utils::filterByType<IterDomain>(serial_loop_roots)) {
+ if (!producer_exact_concrete_root_ids.count(
+ ir_utils::caMapExactConcreteId(serial_loop_root))) {
+ return true;
  }
  }
 
@@ -998,7 +1034,6 @@ class AllocateReuseModifier {
  struct InPlaceSharingInfo {
  bool has_broadcast_between = false;
  bool has_unsupported_op = false;
- bool has_serial_broadcast_resolution_between = false;
  };
 
  //! Careful heavy check on inner sharing candidates,
@@ -1044,13 +1079,6 @@ class AllocateReuseModifier {
  return false;
  }
 
- // TODO: blanket disable reuse across broadcast concretization
- // to unblock issue for now.
- // Should improve the precision of this analysis in a follow up.
- if (topo_info.has_serial_broadcast_resolution_between) {
- return false;
- }
-
  // Get information on the allocated domains of the
  // two buffers
  auto& local_alloc_map = GpuLower::current()->localAllocationInfoMap();
@@ -1103,14 +1131,6 @@ class AllocateReuseModifier {
  info.has_unsupported_op = true;
  }
  }
-
- for (auto in_tv :
- ir_utils::filterByType<TensorView>(tv_def->inputs())) {
- if (all_used_val_set.count(in_tv) &&
- isSerialBroadcastResolution(in_tv, tv)) {
- info.has_serial_broadcast_resolution_between = true;
- }
- }
  }
  }
  return info;