Remove extra uses of ClearAllBits

ArenaBitVector creation guarantees it starts empty. Add a debug
check to make sure this assumption doesn't change.

Note that ArenaAllocator guarantees zero-initialized memory but
ScopedArenaAllocators do not. This is fine either way since the
BitVector constructor calls ClearAllBits.

Bug: 329037671
Test: art/test/testrunner/testrunner.py --host --64 --optimizing -b
Change-Id: Icbf5e5dd1869e80b5d5828ecca9f13de30c0242b

14 files changed, 12 insertions, 55 deletions

diff --git a/compiler/optimizing/code_sinking.cc b/compiler/optimizing/code_sinking.cc
index a2371817ee..0abcaea719 100644
--- a/compiler/optimizing/code_sinking.cc
+++ b/compiler/optimizing/code_sinking.cc
@@ -333,10 +333,9 @@ void CodeSinking::SinkCodeToUncommonBranch(HBasicBlock* end_block) {
 
   size_t number_of_instructions = graph_->GetCurrentInstructionId();
   ScopedArenaVector<HInstruction*> worklist(allocator.Adapter(kArenaAllocMisc));
-  ArenaBitVector processed_instructions(&allocator, number_of_instructions, /* expandable= */ false);
-  processed_instructions.ClearAllBits();
+  ArenaBitVector processed_instructions(
+      &allocator, number_of_instructions, /* expandable= */ false);
   ArenaBitVector post_dominated(&allocator, graph_->GetBlocks().size(), /* expandable= */ false);
-  post_dominated.ClearAllBits();
 
   // Step (1): Visit post order to get a subset of blocks post dominated by `end_block`.
   // TODO(ngeoffray): Getting the full set of post-dominated should be done by
@@ -411,7 +410,6 @@ void CodeSinking::SinkCodeToUncommonBranch(HBasicBlock* end_block) {
   // Step (2): iterate over the worklist to find sinking candidates.
   ArenaBitVector instructions_that_can_move(
       &allocator, number_of_instructions, /* expandable= */ false);
-  instructions_that_can_move.ClearAllBits();
   ScopedArenaVector<ScopedArenaVector<HInstruction*>> instructions_to_move(
       graph_->GetBlocks().size(),
       ScopedArenaVector<HInstruction*>(allocator.Adapter(kArenaAllocMisc)),
diff --git a/compiler/optimizing/constructor_fence_redundancy_elimination.cc b/compiler/optimizing/constructor_fence_redundancy_elimination.cc
index 30c33dd5c5..71fc39a956 100644
--- a/compiler/optimizing/constructor_fence_redundancy_elimination.cc
+++ b/compiler/optimizing/constructor_fence_redundancy_elimination.cc
@@ -52,7 +52,6 @@ class CFREVisitor final : public HGraphVisitor {
       size_t number_of_instructions = GetGraph()->GetCurrentInstructionId();
       candidate_fence_targets_.emplace(
           &scoped_allocator_, number_of_instructions, /*expandable=*/ false, kArenaAllocCFRE);
-      candidate_fence_targets_->ClearAllBits();
     }
 
     for (HInstruction* input : constructor_fence->GetInputs()) {
diff --git a/compiler/optimizing/dead_code_elimination.cc b/compiler/optimizing/dead_code_elimination.cc
index fe1361c935..f44f4b577b 100644
--- a/compiler/optimizing/dead_code_elimination.cc
+++ b/compiler/optimizing/dead_code_elimination.cc
@@ -592,10 +592,7 @@ struct HDeadCodeElimination::TryBelongingInformation {
   TryBelongingInformation(HGraph* graph, ScopedArenaAllocator* allocator)
       : blocks_in_try(allocator, graph->GetBlocks().size(), /*expandable=*/false, kArenaAllocDCE),
         coalesced_try_entries(
-            allocator, graph->GetBlocks().size(), /*expandable=*/false, kArenaAllocDCE) {
-    blocks_in_try.ClearAllBits();
-    coalesced_try_entries.ClearAllBits();
-  }
+            allocator, graph->GetBlocks().size(), /*expandable=*/false, kArenaAllocDCE) {}
 
   // Which blocks belong in the try.
   ArenaBitVector blocks_in_try;
@@ -803,7 +800,6 @@ bool HDeadCodeElimination::RemoveEmptyIfs() {
     ScopedArenaAllocator allocator(graph_->GetArenaStack());
     ArenaBitVector visited_blocks(
         &allocator, graph_->GetBlocks().size(), /*expandable=*/ false, kArenaAllocDCE);
-    visited_blocks.ClearAllBits();
     HBasicBlock* merge_true = true_block;
     visited_blocks.SetBit(merge_true->GetBlockId());
     while (merge_true->IsSingleGoto()) {
@@ -827,7 +823,6 @@ bool HDeadCodeElimination::RemoveEmptyIfs() {
     ScopedArenaQueue<HInstruction*> maybe_remove(allocator.Adapter(kArenaAllocDCE));
     ArenaBitVector visited(
         &allocator, graph_->GetCurrentInstructionId(), /*expandable=*/ false, kArenaAllocDCE);
-    visited.ClearAllBits();
     maybe_remove.push(if_instr->InputAt(0));
     visited.SetBit(if_instr->GetId());
 
@@ -879,7 +874,6 @@ bool HDeadCodeElimination::RemoveDeadBlocks(bool force_recomputation,
 
   // Classify blocks as reachable/unreachable.
   ArenaBitVector live_blocks(&allocator, graph_->GetBlocks().size(), false, kArenaAllocDCE);
-  live_blocks.ClearAllBits();
 
   MarkReachableBlocks(graph_, &live_blocks);
   bool removed_one_or_more_blocks = false;
diff --git a/compiler/optimizing/graph_checker.cc b/compiler/optimizing/graph_checker.cc
index f2662700c7..1ff0d4dc84 100644
--- a/compiler/optimizing/graph_checker.cc
+++ b/compiler/optimizing/graph_checker.cc
@@ -1175,7 +1175,6 @@ void GraphChecker::VisitPhi(HPhi* phi) {
                                  GetGraph()->GetCurrentInstructionId(),
                                  /* expandable= */ false,
                                  kArenaAllocGraphChecker);
-          visited.ClearAllBits();
           if (!IsConstantEquivalent(phi, other_phi, &visited)) {
             AddError(StringPrintf("Two phis (%d and %d) found for VReg %d but they "
                                   "are not equivalents of constants.",
diff --git a/compiler/optimizing/graph_checker.h b/compiler/optimizing/graph_checker.h
index 541a9cc3d2..a1b7b28a24 100644
--- a/compiler/optimizing/graph_checker.h
+++ b/compiler/optimizing/graph_checker.h
@@ -43,9 +43,7 @@ class GraphChecker final : public HGraphDelegateVisitor {
         uses_per_instruction_(allocator_.Adapter(kArenaAllocGraphChecker)),
         instructions_per_block_(allocator_.Adapter(kArenaAllocGraphChecker)),
         phis_per_block_(allocator_.Adapter(kArenaAllocGraphChecker)),
-        codegen_(codegen) {
-    seen_ids_.ClearAllBits();
-  }
+        codegen_(codegen) {}
 
   // Check the whole graph. The pass_change parameter indicates whether changes
   // may have occurred during the just executed pass. The default value is
diff --git a/compiler/optimizing/gvn.cc b/compiler/optimizing/gvn.cc
index 9113860387..cd3b07065c 100644
--- a/compiler/optimizing/gvn.cc
+++ b/compiler/optimizing/gvn.cc
@@ -353,16 +353,13 @@ class ValueSet : public ArenaObject<kArenaAllocGvn> {
  */
 class GlobalValueNumberer : public ValueObject {
  public:
-  GlobalValueNumberer(HGraph* graph,
-                      const SideEffectsAnalysis& side_effects)
+  GlobalValueNumberer(HGraph* graph, const SideEffectsAnalysis& side_effects)
       : graph_(graph),
         allocator_(graph->GetArenaStack()),
         side_effects_(side_effects),
         sets_(graph->GetBlocks().size(), nullptr, allocator_.Adapter(kArenaAllocGvn)),
         visited_blocks_(
-            &allocator_, graph->GetBlocks().size(), /* expandable= */ false, kArenaAllocGvn) {
-    visited_blocks_.ClearAllBits();
-  }
+            &allocator_, graph->GetBlocks().size(), /* expandable= */ false, kArenaAllocGvn) {}
 
   bool Run();
 
diff --git a/compiler/optimizing/instruction_builder.cc b/compiler/optimizing/instruction_builder.cc
index 410d6fd0d0..1d665b2559 100644
--- a/compiler/optimizing/instruction_builder.cc
+++ b/compiler/optimizing/instruction_builder.cc
@@ -538,7 +538,6 @@ ArenaBitVector* HInstructionBuilder::FindNativeDebugInfoLocations() {
                                                      code_item_accessor_.InsnsSizeInCodeUnits(),
                                                      /* expandable= */ false,
                                                      kArenaAllocGraphBuilder);
-  locations->ClearAllBits();
   // The visitor gets called when the line number changes.
   // In other words, it marks the start of new java statement.
   code_item_accessor_.DecodeDebugPositionInfo([&](const DexFile::PositionInfo& entry) {
diff --git a/compiler/optimizing/load_store_analysis.h b/compiler/optimizing/load_store_analysis.h
index 4a630ddf8f..088f5b710f 100644
--- a/compiler/optimizing/load_store_analysis.h
+++ b/compiler/optimizing/load_store_analysis.h
@@ -189,9 +189,7 @@ class HeapLocationCollector : public HGraphVisitor {
         ref_info_array_(allocator->Adapter(kArenaAllocLSA)),
         heap_locations_(allocator->Adapter(kArenaAllocLSA)),
         aliasing_matrix_(allocator, kInitialAliasingMatrixBitVectorSize, true, kArenaAllocLSA),
-        has_heap_stores_(false) {
-    aliasing_matrix_.ClearAllBits();
-  }
+        has_heap_stores_(false) {}
 
   ~HeapLocationCollector() {
     CleanUp();
diff --git a/compiler/optimizing/load_store_elimination.cc b/compiler/optimizing/load_store_elimination.cc
index 80cf9e669b..bd38d8265c 100644
--- a/compiler/optimizing/load_store_elimination.cc
+++ b/compiler/optimizing/load_store_elimination.cc
@@ -1427,9 +1427,8 @@ LSEVisitor::LSEVisitor(HGraph* graph,
       loads_and_stores_(allocator_.Adapter(kArenaAllocLSE)),
       // We may add new instructions (default values, Phis) but we're not adding loads
       // or stores, so we shall not need to resize following vector and BitVector.
-      substitute_instructions_for_loads_(graph->GetCurrentInstructionId(),
-                                         nullptr,
-                                         allocator_.Adapter(kArenaAllocLSE)),
+      substitute_instructions_for_loads_(
+          graph->GetCurrentInstructionId(), nullptr, allocator_.Adapter(kArenaAllocLSE)),
       kept_stores_(&allocator_,
                    /*start_bits=*/graph->GetCurrentInstructionId(),
                    /*expandable=*/false,
@@ -1440,17 +1439,12 @@ LSEVisitor::LSEVisitor(HGraph* graph,
                                                   kArenaAllocLSE),
       loads_requiring_loop_phi_(allocator_.Adapter(kArenaAllocLSE)),
       store_records_(allocator_.Adapter(kArenaAllocLSE)),
-      phi_placeholder_replacements_(num_phi_placeholders_,
-                                    Value::Invalid(),
-                                    allocator_.Adapter(kArenaAllocLSE)),
+      phi_placeholder_replacements_(
+          num_phi_placeholders_, Value::Invalid(), allocator_.Adapter(kArenaAllocLSE)),
       singleton_new_instances_(allocator_.Adapter(kArenaAllocLSE)),
       field_infos_(heap_location_collector_.GetNumberOfHeapLocations(),
                    allocator_.Adapter(kArenaAllocLSE)),
-      current_phase_(Phase::kLoadElimination) {
-  // Clear bit vectors.
-  phi_placeholders_to_search_for_kept_stores_.ClearAllBits();
-  kept_stores_.ClearAllBits();
-}
+      current_phase_(Phase::kLoadElimination) {}
 
 LSEVisitor::Value LSEVisitor::PrepareLoopValue(HBasicBlock* block, size_t idx) {
   // If the pre-header value is known (which implies that the reference dominates this
@@ -1876,7 +1870,6 @@ bool LSEVisitor::TryReplacingLoopPhiPlaceholderWithDefault(
                          /*start_bits=*/ num_phi_placeholders_,
                          /*expandable=*/ false,
                          kArenaAllocLSE);
-  visited.ClearAllBits();
   ScopedArenaVector<PhiPlaceholder> work_queue(allocator.Adapter(kArenaAllocLSE));
 
   // Use depth first search to check if any non-Phi input is unknown.
@@ -1966,7 +1959,6 @@ bool LSEVisitor::TryReplacingLoopPhiPlaceholderWithSingleInput(
                          /*start_bits=*/ num_phi_placeholders_,
                          /*expandable=*/ false,
                          kArenaAllocLSE);
-  visited.ClearAllBits();
   ScopedArenaVector<PhiPlaceholder> work_queue(allocator.Adapter(kArenaAllocLSE));
 
   // Use depth first search to check if any non-Phi input is unknown.
@@ -2278,7 +2270,6 @@ bool LSEVisitor::MaterializeLoopPhis(const ArenaBitVector& phi_placeholders_to_m
     dependencies.push_back(
         ArenaBitVector::Create(&allocator, num_phi_placeholders, kExpandable, kArenaAllocLSE));
     ArenaBitVector* current_dependencies = dependencies.back();
-    current_dependencies->ClearAllBits();
     current_dependencies->SetBit(matrix_index);  // Count the Phi placeholder as its own dependency.
     PhiPlaceholder current_phi_placeholder =
         GetPhiPlaceholderAt(phi_placeholder_indexes[matrix_index]);
@@ -2377,7 +2368,6 @@ std::optional<LSEVisitor::PhiPlaceholder> LSEVisitor::TryToMaterializeLoopPhis(
   // Find Phi placeholders to materialize.
   ArenaBitVector phi_placeholders_to_materialize(
       &allocator, num_phi_placeholders_, /*expandable=*/ false, kArenaAllocLSE);
-  phi_placeholders_to_materialize.ClearAllBits();
   DataType::Type type = load->GetType();
   bool can_use_default_or_phi = IsDefaultOrPhiAllowedForLoad(load);
   std::optional<PhiPlaceholder> loop_phi_with_unknown_input = FindLoopPhisToMaterialize(
@@ -2681,12 +2671,10 @@ void LSEVisitor::FindOldValueForPhiPlaceholder(PhiPlaceholder phi_placeholder,
                          /*start_bits=*/ num_phi_placeholders_,
                          /*expandable=*/ false,
                          kArenaAllocLSE);
-  visited.ClearAllBits();
 
   // Find Phi placeholders to try and match against existing Phis or other replacement values.
   ArenaBitVector phi_placeholders_to_materialize(
       &allocator, num_phi_placeholders_, /*expandable=*/ false, kArenaAllocLSE);
-  phi_placeholders_to_materialize.ClearAllBits();
   std::optional<PhiPlaceholder> loop_phi_with_unknown_input = FindLoopPhisToMaterialize(
       phi_placeholder, &phi_placeholders_to_materialize, type, /*can_use_default_or_phi=*/true);
   if (loop_phi_with_unknown_input) {
@@ -2791,7 +2779,6 @@ void LSEVisitor::FindStoresWritingOldValues() {
                                    /*start_bits=*/ GetGraph()->GetCurrentInstructionId(),
                                    /*expandable=*/ false,
                                    kArenaAllocLSE);
-  eliminated_stores.ClearAllBits();
 
   for (uint32_t store_id : kept_stores_.Indexes()) {
     DCHECK(kept_stores_.IsBitSet(store_id));
diff --git a/compiler/optimizing/nodes.cc b/compiler/optimizing/nodes.cc
index ba268560e8..f2cac19786 100644
--- a/compiler/optimizing/nodes.cc
+++ b/compiler/optimizing/nodes.cc
@@ -72,7 +72,6 @@ void HGraph::FindBackEdges(ArenaBitVector* visited) {
   // Nodes that we're currently visiting, indexed by block id.
   ArenaBitVector visiting(
       &allocator, blocks_.size(), /* expandable= */ false, kArenaAllocGraphBuilder);
-  visiting.ClearAllBits();
   // Number of successors visited from a given node, indexed by block id.
   ScopedArenaVector<size_t> successors_visited(blocks_.size(),
                                                0u,
@@ -219,7 +218,6 @@ GraphAnalysisResult HGraph::BuildDominatorTree() {
   ScopedArenaAllocator allocator(GetArenaStack());
 
   ArenaBitVector visited(&allocator, blocks_.size(), false, kArenaAllocGraphBuilder);
-  visited.ClearAllBits();
 
   // (1) Find the back edges in the graph doing a DFS traversal.
   FindBackEdges(&visited);
@@ -890,7 +888,6 @@ void HLoopInformation::Populate() {
                            graph->GetBlocks().size(),
                            /* expandable= */ false,
                            kArenaAllocGraphBuilder);
-    visited.ClearAllBits();
     // Stop marking blocks at the loop header.
     visited.SetBit(header_->GetBlockId());
 
@@ -1221,7 +1218,6 @@ std::ostream& HInstruction::Dump(std::ostream& os, bool dump_args) {
                            (graph != nullptr) ? graph->GetCurrentInstructionId() : 0u,
                            /* expandable= */ (graph == nullptr),
                            kArenaAllocMisc);
-    visited.ClearAllBits();
     visited.SetBit(GetId());
     // Keep a queue of instructions with their indentations.
     ScopedArenaDeque<std::pair<HInstruction*, size_t>> queue(allocator.Adapter(kArenaAllocMisc));
@@ -1424,7 +1420,6 @@ void HInstruction::ReplaceUsesDominatedBy(HInstruction* dominator,
                            graph->GetBlocks().size(),
                            /* expandable= */ false,
                            kArenaAllocMisc);
-    visited_blocks->ClearAllBits();
     ScopedArenaAllocator allocator(graph->GetArenaStack());
     ScopedArenaQueue<const HBasicBlock*> worklist(allocator.Adapter(kArenaAllocMisc));
     worklist.push(dominator_block);
diff --git a/compiler/optimizing/register_allocator.cc b/compiler/optimizing/register_allocator.cc
index 54a80555dc..1b3a9a6285 100644
--- a/compiler/optimizing/register_allocator.cc
+++ b/compiler/optimizing/register_allocator.cc
@@ -214,7 +214,6 @@ bool RegisterAllocator::ValidateIntervals(ArrayRef<LiveInterval* const> interval
   for (size_t i = 0; i < number_of_registers + number_of_spill_slots; ++i) {
     liveness_of_values.push_back(
         ArenaBitVector::Create(&allocator, max_end, false, kArenaAllocRegisterAllocatorValidate));
-    liveness_of_values.back()->ClearAllBits();
   }
 
   for (LiveInterval* start_interval : intervals) {
diff --git a/compiler/optimizing/ssa_liveness_analysis.h b/compiler/optimizing/ssa_liveness_analysis.h
index cc2b49cf22..e9422edb15 100644
--- a/compiler/optimizing/ssa_liveness_analysis.h
+++ b/compiler/optimizing/ssa_liveness_analysis.h
@@ -41,9 +41,6 @@ class BlockInfo : public ArenaObject<kArenaAllocSsaLiveness> {
         live_out_(allocator, number_of_ssa_values, false, kArenaAllocSsaLiveness),
         kill_(allocator, number_of_ssa_values, false, kArenaAllocSsaLiveness) {
     UNUSED(block_);
-    live_in_.ClearAllBits();
-    live_out_.ClearAllBits();
-    kill_.ClearAllBits();
   }
 
  private:
diff --git a/compiler/optimizing/ssa_phi_elimination.cc b/compiler/optimizing/ssa_phi_elimination.cc
index 1d9be3956a..0796acc687 100644
--- a/compiler/optimizing/ssa_phi_elimination.cc
+++ b/compiler/optimizing/ssa_phi_elimination.cc
@@ -143,7 +143,6 @@ bool SsaRedundantPhiElimination::Run() {
                                        graph_->GetCurrentInstructionId(),
                                        /* expandable= */ false,
                                        kArenaAllocSsaPhiElimination);
-  visited_phis_in_cycle.ClearAllBits();
   ScopedArenaVector<HPhi*> cycle_worklist(allocator.Adapter(kArenaAllocSsaPhiElimination));
 
   while (!worklist.empty()) {
diff --git a/compiler/optimizing/superblock_cloner.cc b/compiler/optimizing/superblock_cloner.cc
index 0a7b95a1fb..e14f7347fb 100644
--- a/compiler/optimizing/superblock_cloner.cc
+++ b/compiler/optimizing/superblock_cloner.cc
@@ -272,8 +272,6 @@ void SuperblockCloner::CopyIncomingEdgesForVersioning() {
 // FindBackEdgesInTheNaturalLoop.
 void SuperblockCloner::FindBackEdgesLocal(HBasicBlock* entry_block, ArenaBitVector* local_set) {
   ArenaBitVector visited(arena_, graph_->GetBlocks().size(), false, kArenaAllocSuperblockCloner);
-  // "visited" must be empty on entry, it's an output argument for all visited (i.e. live) blocks.
-  DCHECK_EQ(visited.GetHighestBitSet(), -1);
 
   // Nodes that we're currently visiting, indexed by block id.
   ArenaBitVector visiting(arena_, graph_->GetBlocks().size(), false, kArenaAllocGraphBuilder);