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

1 files changed, 0 insertions, 5 deletions

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);