2 files changed, 90 insertions, 80 deletions

diff --git a/compiler/optimizing/gvn.cc b/compiler/optimizing/gvn.cc
index 25168b5b0c..6e5f1bd203 100644
--- a/compiler/optimizing/gvn.cc
+++ b/compiler/optimizing/gvn.cc
@@ -91,29 +91,38 @@ SideEffects GlobalValueNumberer::GetBlockEffects(HBasicBlock* block) const {
   return block_effects_.Get(block->GetBlockId());
 }
 
-static bool IsLoopExit(HBasicBlock* block, HBasicBlock* successor) {
-  HLoopInformation* block_info = block->GetLoopInformation();
-  HLoopInformation* other_info = successor->GetLoopInformation();
-  return block_info != other_info && (other_info == nullptr || block_info->IsIn(*other_info));
-}
-
 void GlobalValueNumberer::VisitBasicBlock(HBasicBlock* block) {
-  if (kIsDebugBuild) {
-    // Check that all non back-edge processors have been visited.
-    for (size_t i = 0, e = block->GetPredecessors().Size(); i < e; ++i) {
-      HBasicBlock* predecessor = block->GetPredecessors().Get(i);
-      DCHECK(visited_.Get(predecessor->GetBlockId())
-             || (block->GetLoopInformation() != nullptr
-                 && (block->GetLoopInformation()->GetBackEdges().Get(0) == predecessor)));
+  ValueSet* set = nullptr;
+  const GrowableArray<HBasicBlock*>& predecessors = block->GetPredecessors();
+  if (predecessors.Size() == 0 || predecessors.Get(0)->IsEntryBlock()) {
+    // The entry block should only accumulate constant instructions, and
+    // the builder puts constants only in the entry block.
+    // Therefore, there is no need to propagate the value set to the next block.
+    set = new (allocator_) ValueSet(allocator_);
+  } else {
+    HBasicBlock* dominator = block->GetDominator();
+    set = sets_.Get(dominator->GetBlockId())->Copy();
+    if (dominator->GetSuccessors().Size() != 1 || dominator->GetSuccessors().Get(0) != block) {
+      // We have to copy if the dominator has other successors, or `block` is not a successor
+      // of the dominator.
+      set = set->Copy();
+    }
+    if (!set->IsEmpty()) {
+      if (block->IsLoopHeader()) {
+        DCHECK_EQ(block->GetDominator(), block->GetLoopInformation()->GetPreHeader());
+        set->Kill(GetLoopEffects(block));
+      } else if (predecessors.Size() > 1) {
+        for (size_t i = 0, e = predecessors.Size(); i < e; ++i) {
+          set->IntersectionWith(sets_.Get(predecessors.Get(i)->GetBlockId()));
+          if (set->IsEmpty()) {
+            break;
+          }
+        }
+      }
     }
-    visited_.Put(block->GetBlockId(), true);
   }
 
-  ValueSet* set = sets_.Get(block->GetBlockId());
-
-  if (block->IsLoopHeader()) {
-    set->Kill(GetLoopEffects(block));
-  }
+  sets_.Put(block->GetBlockId(), set);
 
   HInstruction* current = block->GetFirstInstruction();
   while (current != nullptr) {
@@ -131,57 +140,6 @@ void GlobalValueNumberer::VisitBasicBlock(HBasicBlock* block) {
     }
     current = next;
   }
-
-  if (block == graph_->GetEntryBlock()) {
-    // The entry block should only accumulate constant instructions, and
-    // the builder puts constants only in the entry block.
-    // Therefore, there is no need to propagate the value set to the next block.
-    DCHECK_EQ(block->GetDominatedBlocks().Size(), 1u);
-    HBasicBlock* dominated = block->GetDominatedBlocks().Get(0);
-    sets_.Put(dominated->GetBlockId(), new (allocator_) ValueSet(allocator_));
-    return;
-  }
-
-  // Copy the value set to dominated blocks. We can re-use
-  // the current set for the last dominated block because we are done visiting
-  // this block.
-  for (size_t i = 0, e = block->GetDominatedBlocks().Size(); i < e; ++i) {
-    HBasicBlock* dominated = block->GetDominatedBlocks().Get(i);
-    sets_.Put(dominated->GetBlockId(), i == e - 1 ? set : set->Copy());
-  }
-
-  // Kill instructions in the value set of each successor. If the successor
-  // is a loop exit, then we use the side effects of the loop. If not, we use
-  // the side effects of this block.
-  for (size_t i = 0, e = block->GetSuccessors().Size(); i < e; ++i) {
-    HBasicBlock* successor = block->GetSuccessors().Get(i);
-    if (successor->IsLoopHeader()
-        && successor->GetLoopInformation()->GetBackEdges().Get(0) == block) {
-      // In case of a back edge, we already have visited the loop header.
-      // We should not update its value set, because the last dominated block
-      // of the loop header uses the same value set.
-      DCHECK(visited_.Get(successor->GetBlockId()));
-      continue;
-    }
-    DCHECK(!visited_.Get(successor->GetBlockId()));
-    ValueSet* successor_set = sets_.Get(successor->GetBlockId());
-    // The dominator sets the set, and we are guaranteed to have visited it already.
-    DCHECK(successor_set != nullptr);
-
-    // If this block dominates this successor there is nothing to do.
-    // Also if the set is empty, there is nothing to kill.
-    if (successor->GetDominator() != block && !successor_set->IsEmpty()) {
-      if (block->IsInLoop() && IsLoopExit(block, successor)) {
-        // All instructions killed in the loop must be killed for a loop exit.
-        SideEffects effects = GetLoopEffects(block->GetLoopInformation()->GetHeader());
-        sets_.Get(successor->GetBlockId())->Kill(effects);
-      } else {
-        // Following block (that might be in the same loop).
-        // Just kill instructions based on this block's side effects.
-        sets_.Get(successor->GetBlockId())->Kill(GetBlockEffects(block));
-      }
-    }
-  }
 }
 
 }  // namespace art
diff --git a/compiler/optimizing/gvn.h b/compiler/optimizing/gvn.h
index 8e739cb6d3..81f2c3fa87 100644
--- a/compiler/optimizing/gvn.h
+++ b/compiler/optimizing/gvn.h
@@ -96,6 +96,26 @@ class ValueSet : public ArenaObject<kArenaAllocMisc> {
     return nullptr;
   }
 
+  // Returns whether `instruction` is in the set.
+  HInstruction* IdentityLookup(HInstruction* instruction) const {
+    size_t hash_code = instruction->ComputeHashCode();
+    size_t index = hash_code % kDefaultNumberOfEntries;
+    HInstruction* existing = table_[index];
+    if (existing != nullptr && existing == instruction) {
+      return existing;
+    }
+
+    for (ValueSetNode* node = collisions_; node != nullptr; node = node->GetNext()) {
+      if (node->GetHashCode() == hash_code) {
+        existing = node->GetInstruction();
+        if (existing == instruction) {
+          return existing;
+        }
+      }
+    }
+    return nullptr;
+  }
+
   // Removes all instructions in the set that are affected by the given side effects.
   void Kill(SideEffects side_effects) {
     for (size_t i = 0; i < kDefaultNumberOfEntries; ++i) {
@@ -106,9 +126,9 @@ class ValueSet : public ArenaObject<kArenaAllocMisc> {
       }
     }
 
-    ValueSetNode* current = collisions_;
-    ValueSetNode* previous = nullptr;
-    while (current != nullptr) {
+    for (ValueSetNode* current = collisions_, *previous = nullptr;
+         current != nullptr;
+         current = current->GetNext()) {
       HInstruction* instruction = current->GetInstruction();
       if (instruction->GetSideEffects().DependsOn(side_effects)) {
         if (previous == nullptr) {
@@ -120,7 +140,6 @@ class ValueSet : public ArenaObject<kArenaAllocMisc> {
       } else {
         previous = current;
       }
-      current = current->GetNext();
     }
   }
 
@@ -143,6 +162,44 @@ class ValueSet : public ArenaObject<kArenaAllocMisc> {
     return copy;
   }
 
+  void Clear() {
+    number_of_entries_ = 0;
+    collisions_ = nullptr;
+    for (size_t i = 0; i < kDefaultNumberOfEntries; ++i) {
+      table_[i] = nullptr;
+    }
+  }
+
+  // Update this `ValueSet` by intersecting with instructions in `other`.
+  void IntersectionWith(ValueSet* other) {
+    if (IsEmpty()) {
+      return;
+    } else if (other->IsEmpty()) {
+      Clear();
+    } else {
+      for (size_t i = 0; i < kDefaultNumberOfEntries; ++i) {
+        if (table_[i] != nullptr && other->IdentityLookup(table_[i]) == nullptr) {
+          --number_of_entries_;
+          table_[i] = nullptr;
+        }
+      }
+      for (ValueSetNode* current = collisions_, *previous = nullptr;
+           current != nullptr;
+           current = current->GetNext()) {
+        if (other->IdentityLookup(current->GetInstruction()) == nullptr) {
+          if (previous == nullptr) {
+            collisions_ = current->GetNext();
+          } else {
+            previous->SetNext(current->GetNext());
+          }
+          --number_of_entries_;
+        } else {
+          previous = current;
+        }
+      }
+    }
+  }
+
   bool IsEmpty() const { return number_of_entries_ == 0; }
   size_t GetNumberOfEntries() const { return number_of_entries_; }
 
@@ -173,13 +230,11 @@ class GlobalValueNumberer : public ValueObject {
         allocator_(allocator),
         block_effects_(allocator, graph->GetBlocks().Size()),
         loop_effects_(allocator, graph->GetBlocks().Size()),
-        sets_(allocator, graph->GetBlocks().Size()),
-        visited_(allocator, graph->GetBlocks().Size()) {
+        sets_(allocator, graph->GetBlocks().Size()) {
     size_t number_of_blocks = graph->GetBlocks().Size();
     block_effects_.SetSize(number_of_blocks);
     loop_effects_.SetSize(number_of_blocks);
     sets_.SetSize(number_of_blocks);
-    visited_.SetSize(number_of_blocks);
 
     for (size_t i = 0; i < number_of_blocks; ++i) {
       block_effects_.Put(i, SideEffects::None());
@@ -219,9 +274,6 @@ class GlobalValueNumberer : public ValueObject {
   // in the path from the dominator to the block.
   GrowableArray<ValueSet*> sets_;
 
-  // Mark visisted blocks. Only used for debugging.
-  GrowableArray<bool> visited_;
-
   ART_FRIEND_TEST(GVNTest, LoopSideEffects);
   DISALLOW_COPY_AND_ASSIGN(GlobalValueNumberer);
 };