compiler/dex/ssa_transformation.cc - fp2-dev/platform/art - Gitiles

 /*
  * Copyright (C) 2011 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 #include "compiler_internals.h"
 #include "dataflow_iterator-inl.h"

 #define NOTVISITED (-1)

 namespace art {

 void MIRGraph::ClearAllVisitedFlags() {
   AllNodesIterator iter(this);
   for (BasicBlock* bb = iter.Next(); bb != NULL; bb = iter.Next()) {
     bb->visited = false;
   }
 }

 BasicBlock* MIRGraph::NeedsVisit(BasicBlock* bb) {
   if (bb != NULL) {
     if (bb->visited || bb->hidden) {
       bb = NULL;
     }
   }
   return bb;
 }

 BasicBlock* MIRGraph::NextUnvisitedSuccessor(BasicBlock* bb) {
   BasicBlock* res = NeedsVisit(GetBasicBlock(bb->fall_through));
   if (res == NULL) {
     res = NeedsVisit(GetBasicBlock(bb->taken));
     if (res == NULL) {
       if (bb->successor_block_list_type != kNotUsed) {
         GrowableArray<SuccessorBlockInfo*>::Iterator iterator(bb->successor_blocks);
         while (true) {
           SuccessorBlockInfo *sbi = iterator.Next();
           if (sbi == NULL) {
             break;
           }
           res = NeedsVisit(GetBasicBlock(sbi->block));
           if (res != NULL) {
             break;
           }
         }
       }
     }
   }
   return res;
 }

 void MIRGraph::MarkPreOrder(BasicBlock* block) {
   block->visited = true;
   /* Enqueue the pre_order block id */
   if (block->id != NullBasicBlockId) {
     dfs_order_->Insert(block->id);
   }
 }

 void MIRGraph::RecordDFSOrders(BasicBlock* block) {
   std::vector<BasicBlock*> succ;
   MarkPreOrder(block);
   succ.push_back(block);
   while (!succ.empty()) {
     BasicBlock* curr = succ.back();
     BasicBlock* next_successor = NextUnvisitedSuccessor(curr);
     if (next_successor != NULL) {
       MarkPreOrder(next_successor);
       succ.push_back(next_successor);
       continue;
     }
     curr->dfs_id = dfs_post_order_->Size();
     if (curr->id != NullBasicBlockId) {
       dfs_post_order_->Insert(curr->id);
     }
     succ.pop_back();
   }
 }

 /* Sort the blocks by the Depth-First-Search */
 void MIRGraph::ComputeDFSOrders() {
   /* Initialize or reset the DFS pre_order list */
   if (dfs_order_ == NULL) {
     dfs_order_ = new (arena_) GrowableArray<BasicBlockId>(arena_, GetNumBlocks(),
                                                           kGrowableArrayDfsOrder);
   } else {
     /* Just reset the used length on the counter */
     dfs_order_->Reset();
   }

   /* Initialize or reset the DFS post_order list */
   if (dfs_post_order_ == NULL) {
     dfs_post_order_ = new (arena_) GrowableArray<BasicBlockId>(arena_, GetNumBlocks(),
                                                                kGrowableArrayDfsPostOrder);
   } else {
     /* Just reset the used length on the counter */
     dfs_post_order_->Reset();
   }

   // Reset visited flags from all nodes
   ClearAllVisitedFlags();

   // Record dfs orders
   RecordDFSOrders(GetEntryBlock());

   num_reachable_blocks_ = dfs_order_->Size();
 }

 /*
  * Mark block bit on the per-Dalvik register vector to denote that Dalvik
  * register idx is defined in BasicBlock bb.
  */
 bool MIRGraph::FillDefBlockMatrix(BasicBlock* bb) {
   if (bb->data_flow_info == NULL) {
     return false;
   }

   for (uint32_t idx : bb->data_flow_info->def_v->Indexes()) {
     /* Block bb defines register idx */
     def_block_matrix_[idx]->SetBit(bb->id);
   }
   return true;
 }

 void MIRGraph::ComputeDefBlockMatrix() {
   int num_registers = cu_->num_dalvik_registers;
   /* Allocate num_dalvik_registers bit vector pointers */
   def_block_matrix_ = static_cast<ArenaBitVector**>
       (arena_->Alloc(sizeof(ArenaBitVector *) * num_registers,
                      kArenaAllocDFInfo));
   int i;

   /* Initialize num_register vectors with num_blocks bits each */
   for (i = 0; i < num_registers; i++) {
     def_block_matrix_[i] =
         new (arena_) ArenaBitVector(arena_, GetNumBlocks(), false, kBitMapBMatrix);
   }
   AllNodesIterator iter(this);
   for (BasicBlock* bb = iter.Next(); bb != NULL; bb = iter.Next()) {
     FindLocalLiveIn(bb);
   }
   AllNodesIterator iter2(this);
   for (BasicBlock* bb = iter2.Next(); bb != NULL; bb = iter2.Next()) {
     FillDefBlockMatrix(bb);
   }

   /*
    * Also set the incoming parameters as defs in the entry block.
    * Only need to handle the parameters for the outer method.
    */
   int num_regs = cu_->num_dalvik_registers;
   int in_reg = num_regs - cu_->num_ins;
   for (; in_reg < num_regs; in_reg++) {
     def_block_matrix_[in_reg]->SetBit(GetEntryBlock()->id);
   }
 }

 void MIRGraph::ComputeDomPostOrderTraversal(BasicBlock* bb) {
   if (dom_post_order_traversal_ == NULL || max_num_reachable_blocks_ < num_reachable_blocks_) {
     // First time or too small - create the array.
     dom_post_order_traversal_ =
         new (arena_) GrowableArray<BasicBlockId>(arena_, num_reachable_blocks_,
                                         kGrowableArrayDomPostOrderTraversal);
   } else {
     dom_post_order_traversal_->Reset();
   }
   ClearAllVisitedFlags();
   std::vector<std::pair<BasicBlock*, ArenaBitVector::IndexIterator>> work_stack;
   bb->visited = true;
   work_stack.push_back(std::make_pair(bb, bb->i_dominated->Indexes().begin()));
   while (!work_stack.empty()) {
     std::pair<BasicBlock*, ArenaBitVector::IndexIterator>* curr = &work_stack.back();
     BasicBlock* curr_bb = curr->first;
     ArenaBitVector::IndexIterator* curr_idom_iter = &curr->second;
     while (!curr_idom_iter->Done() && (NeedsVisit(GetBasicBlock(**curr_idom_iter)) == nullptr)) {
       ++*curr_idom_iter;
     }
     // NOTE: work_stack.push_back()/pop_back() invalidate curr and curr_idom_iter.
     if (!curr_idom_iter->Done()) {
       BasicBlock* new_bb = GetBasicBlock(**curr_idom_iter);
       ++*curr_idom_iter;
       new_bb->visited = true;
       work_stack.push_back(std::make_pair(new_bb, new_bb->i_dominated->Indexes().begin()));
     } else {
       // no successor/next
       if (curr_bb->id != NullBasicBlockId) {
         dom_post_order_traversal_->Insert(curr_bb->id);
       }
       work_stack.pop_back();

       /* hacky loop detection */
       if ((curr_bb->taken != NullBasicBlockId) && curr_bb->dominators->IsBitSet(curr_bb->taken)) {
         curr_bb->nesting_depth++;
         attributes_ |= METHOD_HAS_LOOP;
       }
     }
   }
 }

 void MIRGraph::CheckForDominanceFrontier(BasicBlock* dom_bb,
                                          const BasicBlock* succ_bb) {
   /*
    * TODO - evaluate whether phi will ever need to be inserted into exit
    * blocks.
    */
   if (succ_bb->i_dom != dom_bb->id &&
     succ_bb->block_type == kDalvikByteCode &&
     succ_bb->hidden == false) {
     dom_bb->dom_frontier->SetBit(succ_bb->id);
   }
 }

 /* Worker function to compute the dominance frontier */
 bool MIRGraph::ComputeDominanceFrontier(BasicBlock* bb) {
   /* Calculate DF_local */
   if (bb->taken != NullBasicBlockId) {
     CheckForDominanceFrontier(bb, GetBasicBlock(bb->taken));
   }
   if (bb->fall_through != NullBasicBlockId) {
     CheckForDominanceFrontier(bb, GetBasicBlock(bb->fall_through));
   }
   if (bb->successor_block_list_type != kNotUsed) {
     GrowableArray<SuccessorBlockInfo*>::Iterator iterator(bb->successor_blocks);
       while (true) {
         SuccessorBlockInfo *successor_block_info = iterator.Next();
         if (successor_block_info == NULL) {
           break;
         }
         BasicBlock* succ_bb = GetBasicBlock(successor_block_info->block);
         CheckForDominanceFrontier(bb, succ_bb);
       }
   }

   /* Calculate DF_up */
   for (uint32_t dominated_idx : bb->i_dominated->Indexes()) {
     BasicBlock* dominated_bb = GetBasicBlock(dominated_idx);
     for (uint32_t df_up_block_idx : dominated_bb->dom_frontier->Indexes()) {
       BasicBlock* df_up_block = GetBasicBlock(df_up_block_idx);
       CheckForDominanceFrontier(bb, df_up_block);
     }
   }

   return true;
 }

 /* Worker function for initializing domination-related data structures */
 void MIRGraph::InitializeDominationInfo(BasicBlock* bb) {
   int num_total_blocks = GetBasicBlockListCount();

   if (bb->dominators == NULL) {
     bb->dominators = new (arena_) ArenaBitVector(arena_, num_total_blocks,
                                                  false /* expandable */, kBitMapDominators);
     bb->i_dominated = new (arena_) ArenaBitVector(arena_, num_total_blocks,
                                                   false /* expandable */, kBitMapIDominated);
     bb->dom_frontier = new (arena_) ArenaBitVector(arena_, num_total_blocks,
                                                    false /* expandable */, kBitMapDomFrontier);
   } else {
     bb->dominators->ClearAllBits();
     bb->i_dominated->ClearAllBits();
     bb->dom_frontier->ClearAllBits();
   }
   /* Set all bits in the dominator vector */
   bb->dominators->SetInitialBits(num_total_blocks);

   return;
 }

 /*
  * Walk through the ordered i_dom list until we reach common parent.
  * Given the ordering of i_dom_list, this common parent represents the
  * last element of the intersection of block1 and block2 dominators.
   */
 int MIRGraph::FindCommonParent(int block1, int block2) {
   while (block1 != block2) {
     while (block1 < block2) {
       block1 = i_dom_list_[block1];
       DCHECK_NE(block1, NOTVISITED);
     }
     while (block2 < block1) {
       block2 = i_dom_list_[block2];
       DCHECK_NE(block2, NOTVISITED);
     }
   }
   return block1;
 }

 /* Worker function to compute each block's immediate dominator */
 bool MIRGraph::ComputeblockIDom(BasicBlock* bb) {
   /* Special-case entry block */
   if ((bb->id == NullBasicBlockId) || (bb == GetEntryBlock())) {
     return false;
   }

   /* Iterate through the predecessors */
   GrowableArray<BasicBlockId>::Iterator iter(bb->predecessors);

   /* Find the first processed predecessor */
   int idom = -1;
   while (true) {
     BasicBlock* pred_bb = GetBasicBlock(iter.Next());
     CHECK(pred_bb != NULL);
     if (i_dom_list_[pred_bb->dfs_id] != NOTVISITED) {
       idom = pred_bb->dfs_id;
       break;
     }
   }

   /* Scan the rest of the predecessors */
   while (true) {
       BasicBlock* pred_bb = GetBasicBlock(iter.Next());
       if (!pred_bb) {
         break;
       }
       if (i_dom_list_[pred_bb->dfs_id] == NOTVISITED) {
         continue;
       } else {
         idom = FindCommonParent(pred_bb->dfs_id, idom);
       }
   }

   DCHECK_NE(idom, NOTVISITED);

   /* Did something change? */
   if (i_dom_list_[bb->dfs_id] != idom) {
     i_dom_list_[bb->dfs_id] = idom;
     return true;
   }
   return false;
 }

 /* Worker function to compute each block's domintors */
 bool MIRGraph::ComputeBlockDominators(BasicBlock* bb) {
   if (bb == GetEntryBlock()) {
     bb->dominators->ClearAllBits();
   } else {
     bb->dominators->Copy(GetBasicBlock(bb->i_dom)->dominators);
   }
   bb->dominators->SetBit(bb->id);
   return false;
 }

 bool MIRGraph::SetDominators(BasicBlock* bb) {
   if (bb != GetEntryBlock()) {
     int idom_dfs_idx = i_dom_list_[bb->dfs_id];
     DCHECK_NE(idom_dfs_idx, NOTVISITED);
     int i_dom_idx = dfs_post_order_->Get(idom_dfs_idx);
     BasicBlock* i_dom = GetBasicBlock(i_dom_idx);
     bb->i_dom = i_dom->id;
     /* Add bb to the i_dominated set of the immediate dominator block */
     i_dom->i_dominated->SetBit(bb->id);
   }
   return false;
 }

 /* Compute dominators, immediate dominator, and dominance fronter */
 void MIRGraph::ComputeDominators() {
   int num_reachable_blocks = num_reachable_blocks_;

   /* Initialize domination-related data structures */
   PreOrderDfsIterator iter(this);
   for (BasicBlock* bb = iter.Next(); bb != NULL; bb = iter.Next()) {
     InitializeDominationInfo(bb);
   }

   /* Initialize & Clear i_dom_list */
   if (max_num_reachable_blocks_ < num_reachable_blocks_) {
     i_dom_list_ = static_cast<int*>(arena_->Alloc(sizeof(int) * num_reachable_blocks,
                                                   kArenaAllocDFInfo));
   }
   for (int i = 0; i < num_reachable_blocks; i++) {
     i_dom_list_[i] = NOTVISITED;
   }

   /* For post-order, last block is entry block.  Set its i_dom to istelf */
   DCHECK_EQ(GetEntryBlock()->dfs_id, num_reachable_blocks-1);
   i_dom_list_[GetEntryBlock()->dfs_id] = GetEntryBlock()->dfs_id;

   /* Compute the immediate dominators */
   RepeatingReversePostOrderDfsIterator iter2(this);
   bool change = false;
   for (BasicBlock* bb = iter2.Next(false); bb != NULL; bb = iter2.Next(change)) {
     change = ComputeblockIDom(bb);
   }

   /* Set the dominator for the root node */
   GetEntryBlock()->dominators->ClearAllBits();
   GetEntryBlock()->dominators->SetBit(GetEntryBlock()->id);

   GetEntryBlock()->i_dom = 0;

   PreOrderDfsIterator iter3(this);
   for (BasicBlock* bb = iter3.Next(); bb != NULL; bb = iter3.Next()) {
     SetDominators(bb);
   }

   ReversePostOrderDfsIterator iter4(this);
   for (BasicBlock* bb = iter4.Next(); bb != NULL; bb = iter4.Next()) {
     ComputeBlockDominators(bb);
   }

   // Compute the dominance frontier for each block.
   ComputeDomPostOrderTraversal(GetEntryBlock());
   PostOrderDOMIterator iter5(this);
   for (BasicBlock* bb = iter5.Next(); bb != NULL; bb = iter5.Next()) {
     ComputeDominanceFrontier(bb);
   }
 }

 /*
  * Perform dest U= src1 ^ ~src2
  * This is probably not general enough to be placed in BitVector.[ch].
  */
 void MIRGraph::ComputeSuccLineIn(ArenaBitVector* dest, const ArenaBitVector* src1,
                                  const ArenaBitVector* src2) {
   if (dest->GetStorageSize() != src1->GetStorageSize() ||
       dest->GetStorageSize() != src2->GetStorageSize() ||
       dest->IsExpandable() != src1->IsExpandable() ||
       dest->IsExpandable() != src2->IsExpandable()) {
     LOG(FATAL) << "Incompatible set properties";
   }

   unsigned int idx;
   for (idx = 0; idx < dest->GetStorageSize(); idx++) {
     dest->GetRawStorage()[idx] |= src1->GetRawStorageWord(idx) & ~(src2->GetRawStorageWord(idx));
   }
 }

 /*
  * Iterate through all successor blocks and propagate up the live-in sets.
  * The calculated result is used for phi-node pruning - where we only need to
  * insert a phi node if the variable is live-in to the block.
  */
 bool MIRGraph::ComputeBlockLiveIns(BasicBlock* bb) {
   DCHECK_EQ(temp_bit_vector_size_, cu_->num_dalvik_registers);
   ArenaBitVector* temp_dalvik_register_v = temp_bit_vector_;

   if (bb->data_flow_info == NULL) {
     return false;
   }
   temp_dalvik_register_v->Copy(bb->data_flow_info->live_in_v);
   BasicBlock* bb_taken = GetBasicBlock(bb->taken);
   BasicBlock* bb_fall_through = GetBasicBlock(bb->fall_through);
   if (bb_taken && bb_taken->data_flow_info)
     ComputeSuccLineIn(temp_dalvik_register_v, bb_taken->data_flow_info->live_in_v,
                       bb->data_flow_info->def_v);
   if (bb_fall_through && bb_fall_through->data_flow_info)
     ComputeSuccLineIn(temp_dalvik_register_v, bb_fall_through->data_flow_info->live_in_v,
                       bb->data_flow_info->def_v);
   if (bb->successor_block_list_type != kNotUsed) {
     GrowableArray<SuccessorBlockInfo*>::Iterator iterator(bb->successor_blocks);
     while (true) {
       SuccessorBlockInfo *successor_block_info = iterator.Next();
       if (successor_block_info == NULL) {
         break;
       }
       BasicBlock* succ_bb = GetBasicBlock(successor_block_info->block);
       if (succ_bb->data_flow_info) {
         ComputeSuccLineIn(temp_dalvik_register_v, succ_bb->data_flow_info->live_in_v,
                           bb->data_flow_info->def_v);
       }
     }
   }
   if (!temp_dalvik_register_v->Equal(bb->data_flow_info->live_in_v)) {
     bb->data_flow_info->live_in_v->Copy(temp_dalvik_register_v);
     return true;
   }
   return false;
 }

 /* Insert phi nodes to for each variable to the dominance frontiers */
 void MIRGraph::InsertPhiNodes() {
   int dalvik_reg;
   ArenaBitVector* phi_blocks = new (temp_scoped_alloc_.get()) ArenaBitVector(
       temp_scoped_alloc_.get(), GetNumBlocks(), false, kBitMapPhi);
   ArenaBitVector* input_blocks = new (temp_scoped_alloc_.get()) ArenaBitVector(
       temp_scoped_alloc_.get(), GetNumBlocks(), false, kBitMapInputBlocks);

   RepeatingPostOrderDfsIterator iter(this);
   bool change = false;
   for (BasicBlock* bb = iter.Next(false); bb != NULL; bb = iter.Next(change)) {
     change = ComputeBlockLiveIns(bb);
   }

   /* Iterate through each Dalvik register */
   for (dalvik_reg = cu_->num_dalvik_registers - 1; dalvik_reg >= 0; dalvik_reg--) {
     input_blocks->Copy(def_block_matrix_[dalvik_reg]);
     phi_blocks->ClearAllBits();
     do {
       // TUNING: When we repeat this, we could skip indexes from the previous pass.
       for (uint32_t idx : input_blocks->Indexes()) {
         BasicBlock* def_bb = GetBasicBlock(idx);
         if (def_bb->dom_frontier != nullptr) {
           phi_blocks->Union(def_bb->dom_frontier);
         }
       }
     } while (input_blocks->Union(phi_blocks));

     /*
      * Insert a phi node for dalvik_reg in the phi_blocks if the Dalvik
      * register is in the live-in set.
      */
     for (uint32_t idx : phi_blocks->Indexes()) {
       BasicBlock* phi_bb = GetBasicBlock(idx);
       /* Variable will be clobbered before being used - no need for phi */
       if (!phi_bb->data_flow_info->live_in_v->IsBitSet(dalvik_reg)) {
         continue;
       }
       MIR *phi = NewMIR();
       phi->dalvikInsn.opcode = static_cast<Instruction::Code>(kMirOpPhi);
       phi->dalvikInsn.vA = dalvik_reg;
       phi->offset = phi_bb->start_offset;
       phi->m_unit_index = 0;  // Arbitrarily assign all Phi nodes to outermost method.
       phi_bb->PrependMIR(phi);
     }
   }
 }

 /*
  * Worker function to insert phi-operands with latest SSA names from
  * predecessor blocks
  */
 bool MIRGraph::InsertPhiNodeOperands(BasicBlock* bb) {
   /* Phi nodes are at the beginning of each block */
   for (MIR* mir = bb->first_mir_insn; mir != NULL; mir = mir->next) {
     if (mir->dalvikInsn.opcode != static_cast<Instruction::Code>(kMirOpPhi))
       return true;
     int ssa_reg = mir->ssa_rep->defs[0];
     DCHECK_GE(ssa_reg, 0);   // Shouldn't see compiler temps here
     int v_reg = SRegToVReg(ssa_reg);

     /* Iterate through the predecessors */
     GrowableArray<BasicBlockId>::Iterator iter(bb->predecessors);
     size_t num_uses = bb->predecessors->Size();
     AllocateSSAUseData(mir, num_uses);
     int* uses = mir->ssa_rep->uses;
     BasicBlockId* incoming =
         static_cast<BasicBlockId*>(arena_->Alloc(sizeof(BasicBlockId) * num_uses,
                                                  kArenaAllocDFInfo));
     mir->meta.phi_incoming = incoming;
     int idx = 0;
     while (true) {
       BasicBlock* pred_bb = GetBasicBlock(iter.Next());
       if (!pred_bb) {
        break;
       }
       int ssa_reg = pred_bb->data_flow_info->vreg_to_ssa_map_exit[v_reg];
       uses[idx] = ssa_reg;
       incoming[idx] = pred_bb->id;
       idx++;
     }
   }

   return true;
 }

 void MIRGraph::DoDFSPreOrderSSARename(BasicBlock* block) {
   if (block->visited || block->hidden) {
     return;
   }
   block->visited = true;

   /* Process this block */
   DoSSAConversion(block);
   int map_size = sizeof(int) * cu_->num_dalvik_registers;

   /* Save SSA map snapshot */
   ScopedArenaAllocator allocator(&cu_->arena_stack);
   int* saved_ssa_map =
       static_cast<int*>(allocator.Alloc(map_size, kArenaAllocDalvikToSSAMap));
   memcpy(saved_ssa_map, vreg_to_ssa_map_, map_size);

   if (block->fall_through != NullBasicBlockId) {
     DoDFSPreOrderSSARename(GetBasicBlock(block->fall_through));
     /* Restore SSA map snapshot */
     memcpy(vreg_to_ssa_map_, saved_ssa_map, map_size);
   }
   if (block->taken != NullBasicBlockId) {
     DoDFSPreOrderSSARename(GetBasicBlock(block->taken));
     /* Restore SSA map snapshot */
     memcpy(vreg_to_ssa_map_, saved_ssa_map, map_size);
   }
   if (block->successor_block_list_type != kNotUsed) {
     GrowableArray<SuccessorBlockInfo*>::Iterator iterator(block->successor_blocks);
     while (true) {
       SuccessorBlockInfo *successor_block_info = iterator.Next();
       if (successor_block_info == NULL) {
         break;
       }
       BasicBlock* succ_bb = GetBasicBlock(successor_block_info->block);
       DoDFSPreOrderSSARename(succ_bb);
       /* Restore SSA map snapshot */
       memcpy(vreg_to_ssa_map_, saved_ssa_map, map_size);
     }
   }
   return;
 }

 }  // namespace art
	/*
	* Copyright (C) 2011 The Android Open Source Project
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	#include "compiler_internals.h"
	#include "dataflow_iterator-inl.h"

	#define NOTVISITED (-1)

	namespace art {

	void MIRGraph::ClearAllVisitedFlags() {
	AllNodesIterator iter(this);
	for (BasicBlock* bb = iter.Next(); bb != NULL; bb = iter.Next()) {
	bb->visited = false;
	}
	}

	BasicBlock* MIRGraph::NeedsVisit(BasicBlock* bb) {
	if (bb != NULL) {
	if (bb->visited \|\| bb->hidden) {
	bb = NULL;
	}
	}
	return bb;
	}

	BasicBlock* MIRGraph::NextUnvisitedSuccessor(BasicBlock* bb) {
	BasicBlock* res = NeedsVisit(GetBasicBlock(bb->fall_through));
	if (res == NULL) {
	res = NeedsVisit(GetBasicBlock(bb->taken));
	if (res == NULL) {
	if (bb->successor_block_list_type != kNotUsed) {
	GrowableArray<SuccessorBlockInfo*>::Iterator iterator(bb->successor_blocks);
	while (true) {
	SuccessorBlockInfo *sbi = iterator.Next();
	if (sbi == NULL) {
	break;
	}
	res = NeedsVisit(GetBasicBlock(sbi->block));
	if (res != NULL) {
	break;
	}
	}
	}
	}
	}
	return res;
	}

	void MIRGraph::MarkPreOrder(BasicBlock* block) {
	block->visited = true;
	/* Enqueue the pre_order block id */
	if (block->id != NullBasicBlockId) {
	dfs_order_->Insert(block->id);
	}
	}

	void MIRGraph::RecordDFSOrders(BasicBlock* block) {
	std::vector<BasicBlock*> succ;
	MarkPreOrder(block);
	succ.push_back(block);
	while (!succ.empty()) {
	BasicBlock* curr = succ.back();
	BasicBlock* next_successor = NextUnvisitedSuccessor(curr);
	if (next_successor != NULL) {
	MarkPreOrder(next_successor);
	succ.push_back(next_successor);
	continue;
	}
	curr->dfs_id = dfs_post_order_->Size();
	if (curr->id != NullBasicBlockId) {
	dfs_post_order_->Insert(curr->id);
	}
	succ.pop_back();
	}
	}

	/* Sort the blocks by the Depth-First-Search */
	void MIRGraph::ComputeDFSOrders() {
	/* Initialize or reset the DFS pre_order list */
	if (dfs_order_ == NULL) {
	dfs_order_ = new (arena_) GrowableArray<BasicBlockId>(arena_, GetNumBlocks(),
	kGrowableArrayDfsOrder);
	} else {
	/* Just reset the used length on the counter */
	dfs_order_->Reset();
	}

	/* Initialize or reset the DFS post_order list */
	if (dfs_post_order_ == NULL) {
	dfs_post_order_ = new (arena_) GrowableArray<BasicBlockId>(arena_, GetNumBlocks(),
	kGrowableArrayDfsPostOrder);
	} else {
	/* Just reset the used length on the counter */
	dfs_post_order_->Reset();
	}

	// Reset visited flags from all nodes
	ClearAllVisitedFlags();

	// Record dfs orders
	RecordDFSOrders(GetEntryBlock());

	num_reachable_blocks_ = dfs_order_->Size();
	}

	/*
	* Mark block bit on the per-Dalvik register vector to denote that Dalvik
	* register idx is defined in BasicBlock bb.
	*/
	bool MIRGraph::FillDefBlockMatrix(BasicBlock* bb) {
	if (bb->data_flow_info == NULL) {
	return false;
	}

	for (uint32_t idx : bb->data_flow_info->def_v->Indexes()) {
	/* Block bb defines register idx */
	def_block_matrix_[idx]->SetBit(bb->id);
	}
	return true;
	}

	void MIRGraph::ComputeDefBlockMatrix() {
	int num_registers = cu_->num_dalvik_registers;
	/* Allocate num_dalvik_registers bit vector pointers */
	def_block_matrix_ = static_cast<ArenaBitVector**>
	(arena_->Alloc(sizeof(ArenaBitVector ) num_registers,
	kArenaAllocDFInfo));
	int i;

	/* Initialize num_register vectors with num_blocks bits each */
	for (i = 0; i < num_registers; i++) {
	def_block_matrix_[i] =
	new (arena_) ArenaBitVector(arena_, GetNumBlocks(), false, kBitMapBMatrix);
	}
	AllNodesIterator iter(this);
	for (BasicBlock* bb = iter.Next(); bb != NULL; bb = iter.Next()) {
	FindLocalLiveIn(bb);
	}
	AllNodesIterator iter2(this);
	for (BasicBlock* bb = iter2.Next(); bb != NULL; bb = iter2.Next()) {
	FillDefBlockMatrix(bb);
	}

	/*
	* Also set the incoming parameters as defs in the entry block.
	* Only need to handle the parameters for the outer method.
	*/
	int num_regs = cu_->num_dalvik_registers;
	int in_reg = num_regs - cu_->num_ins;
	for (; in_reg < num_regs; in_reg++) {
	def_block_matrix_[in_reg]->SetBit(GetEntryBlock()->id);
	}
	}

	void MIRGraph::ComputeDomPostOrderTraversal(BasicBlock* bb) {
	if (dom_post_order_traversal_ == NULL \|\| max_num_reachable_blocks_ < num_reachable_blocks_) {
	// First time or too small - create the array.
	dom_post_order_traversal_ =
	new (arena_) GrowableArray<BasicBlockId>(arena_, num_reachable_blocks_,
	kGrowableArrayDomPostOrderTraversal);
	} else {
	dom_post_order_traversal_->Reset();
	}
	ClearAllVisitedFlags();
	std::vector<std::pair<BasicBlock*, ArenaBitVector::IndexIterator>> work_stack;
	bb->visited = true;
	work_stack.push_back(std::make_pair(bb, bb->i_dominated->Indexes().begin()));
	while (!work_stack.empty()) {
	std::pair<BasicBlock, ArenaBitVector::IndexIterator> curr = &work_stack.back();
	BasicBlock* curr_bb = curr->first;
	ArenaBitVector::IndexIterator* curr_idom_iter = &curr->second;
	while (!curr_idom_iter->Done() && (NeedsVisit(GetBasicBlock(**curr_idom_iter)) == nullptr)) {
	++*curr_idom_iter;
	}
	// NOTE: work_stack.push_back()/pop_back() invalidate curr and curr_idom_iter.
	if (!curr_idom_iter->Done()) {
	BasicBlock* new_bb = GetBasicBlock(**curr_idom_iter);
	++*curr_idom_iter;
	new_bb->visited = true;
	work_stack.push_back(std::make_pair(new_bb, new_bb->i_dominated->Indexes().begin()));
	} else {
	// no successor/next
	if (curr_bb->id != NullBasicBlockId) {
	dom_post_order_traversal_->Insert(curr_bb->id);
	}
	work_stack.pop_back();

	/* hacky loop detection */
	if ((curr_bb->taken != NullBasicBlockId) && curr_bb->dominators->IsBitSet(curr_bb->taken)) {
	curr_bb->nesting_depth++;
	attributes_ \|= METHOD_HAS_LOOP;
	}
	}
	}
	}

	void MIRGraph::CheckForDominanceFrontier(BasicBlock* dom_bb,
	const BasicBlock* succ_bb) {
	/*
	* TODO - evaluate whether phi will ever need to be inserted into exit
	* blocks.
	*/
	if (succ_bb->i_dom != dom_bb->id &&
	succ_bb->block_type == kDalvikByteCode &&
	succ_bb->hidden == false) {
	dom_bb->dom_frontier->SetBit(succ_bb->id);
	}
	}

	/* Worker function to compute the dominance frontier */
	bool MIRGraph::ComputeDominanceFrontier(BasicBlock* bb) {
	/* Calculate DF_local */
	if (bb->taken != NullBasicBlockId) {
	CheckForDominanceFrontier(bb, GetBasicBlock(bb->taken));
	}
	if (bb->fall_through != NullBasicBlockId) {
	CheckForDominanceFrontier(bb, GetBasicBlock(bb->fall_through));
	}
	if (bb->successor_block_list_type != kNotUsed) {
	GrowableArray<SuccessorBlockInfo*>::Iterator iterator(bb->successor_blocks);
	while (true) {
	SuccessorBlockInfo *successor_block_info = iterator.Next();
	if (successor_block_info == NULL) {
	break;
	}
	BasicBlock* succ_bb = GetBasicBlock(successor_block_info->block);
	CheckForDominanceFrontier(bb, succ_bb);
	}
	}

	/* Calculate DF_up */
	for (uint32_t dominated_idx : bb->i_dominated->Indexes()) {
	BasicBlock* dominated_bb = GetBasicBlock(dominated_idx);
	for (uint32_t df_up_block_idx : dominated_bb->dom_frontier->Indexes()) {
	BasicBlock* df_up_block = GetBasicBlock(df_up_block_idx);
	CheckForDominanceFrontier(bb, df_up_block);
	}
	}

	return true;
	}

	/* Worker function for initializing domination-related data structures */
	void MIRGraph::InitializeDominationInfo(BasicBlock* bb) {
	int num_total_blocks = GetBasicBlockListCount();

	if (bb->dominators == NULL) {
	bb->dominators = new (arena_) ArenaBitVector(arena_, num_total_blocks,
	false /* expandable */, kBitMapDominators);
	bb->i_dominated = new (arena_) ArenaBitVector(arena_, num_total_blocks,
	false /* expandable */, kBitMapIDominated);
	bb->dom_frontier = new (arena_) ArenaBitVector(arena_, num_total_blocks,
	false /* expandable */, kBitMapDomFrontier);
	} else {
	bb->dominators->ClearAllBits();
	bb->i_dominated->ClearAllBits();
	bb->dom_frontier->ClearAllBits();
	}
	/* Set all bits in the dominator vector */
	bb->dominators->SetInitialBits(num_total_blocks);

	return;
	}

	/*
	* Walk through the ordered i_dom list until we reach common parent.
	* Given the ordering of i_dom_list, this common parent represents the
	* last element of the intersection of block1 and block2 dominators.
	*/
	int MIRGraph::FindCommonParent(int block1, int block2) {
	while (block1 != block2) {
	while (block1 < block2) {
	block1 = i_dom_list_[block1];
	DCHECK_NE(block1, NOTVISITED);
	}
	while (block2 < block1) {
	block2 = i_dom_list_[block2];
	DCHECK_NE(block2, NOTVISITED);
	}
	}
	return block1;
	}

	/* Worker function to compute each block's immediate dominator */
	bool MIRGraph::ComputeblockIDom(BasicBlock* bb) {
	/* Special-case entry block */
	if ((bb->id == NullBasicBlockId) \|\| (bb == GetEntryBlock())) {
	return false;
	}

	/* Iterate through the predecessors */
	GrowableArray<BasicBlockId>::Iterator iter(bb->predecessors);

	/* Find the first processed predecessor */
	int idom = -1;
	while (true) {
	BasicBlock* pred_bb = GetBasicBlock(iter.Next());
	CHECK(pred_bb != NULL);
	if (i_dom_list_[pred_bb->dfs_id] != NOTVISITED) {
	idom = pred_bb->dfs_id;
	break;
	}
	}

	/* Scan the rest of the predecessors */
	while (true) {
	BasicBlock* pred_bb = GetBasicBlock(iter.Next());
	if (!pred_bb) {
	break;
	}
	if (i_dom_list_[pred_bb->dfs_id] == NOTVISITED) {
	continue;
	} else {
	idom = FindCommonParent(pred_bb->dfs_id, idom);
	}
	}

	DCHECK_NE(idom, NOTVISITED);

	/* Did something change? */
	if (i_dom_list_[bb->dfs_id] != idom) {
	i_dom_list_[bb->dfs_id] = idom;
	return true;
	}
	return false;
	}

	/* Worker function to compute each block's domintors */
	bool MIRGraph::ComputeBlockDominators(BasicBlock* bb) {
	if (bb == GetEntryBlock()) {
	bb->dominators->ClearAllBits();
	} else {
	bb->dominators->Copy(GetBasicBlock(bb->i_dom)->dominators);
	}
	bb->dominators->SetBit(bb->id);
	return false;
	}

	bool MIRGraph::SetDominators(BasicBlock* bb) {
	if (bb != GetEntryBlock()) {
	int idom_dfs_idx = i_dom_list_[bb->dfs_id];
	DCHECK_NE(idom_dfs_idx, NOTVISITED);
	int i_dom_idx = dfs_post_order_->Get(idom_dfs_idx);
	BasicBlock* i_dom = GetBasicBlock(i_dom_idx);
	bb->i_dom = i_dom->id;
	/* Add bb to the i_dominated set of the immediate dominator block */
	i_dom->i_dominated->SetBit(bb->id);
	}
	return false;
	}

	/* Compute dominators, immediate dominator, and dominance fronter */
	void MIRGraph::ComputeDominators() {
	int num_reachable_blocks = num_reachable_blocks_;

	/* Initialize domination-related data structures */
	PreOrderDfsIterator iter(this);
	for (BasicBlock* bb = iter.Next(); bb != NULL; bb = iter.Next()) {
	InitializeDominationInfo(bb);
	}

	/* Initialize & Clear i_dom_list */
	if (max_num_reachable_blocks_ < num_reachable_blocks_) {
	i_dom_list_ = static_cast<int>(arena_->Alloc(sizeof(int) num_reachable_blocks,
	kArenaAllocDFInfo));
	}
	for (int i = 0; i < num_reachable_blocks; i++) {
	i_dom_list_[i] = NOTVISITED;
	}

	/* For post-order, last block is entry block. Set its i_dom to istelf */
	DCHECK_EQ(GetEntryBlock()->dfs_id, num_reachable_blocks-1);
	i_dom_list_[GetEntryBlock()->dfs_id] = GetEntryBlock()->dfs_id;

	/* Compute the immediate dominators */
	RepeatingReversePostOrderDfsIterator iter2(this);
	bool change = false;
	for (BasicBlock* bb = iter2.Next(false); bb != NULL; bb = iter2.Next(change)) {
	change = ComputeblockIDom(bb);
	}

	/* Set the dominator for the root node */
	GetEntryBlock()->dominators->ClearAllBits();
	GetEntryBlock()->dominators->SetBit(GetEntryBlock()->id);

	GetEntryBlock()->i_dom = 0;

	PreOrderDfsIterator iter3(this);
	for (BasicBlock* bb = iter3.Next(); bb != NULL; bb = iter3.Next()) {
	SetDominators(bb);
	}

	ReversePostOrderDfsIterator iter4(this);
	for (BasicBlock* bb = iter4.Next(); bb != NULL; bb = iter4.Next()) {
	ComputeBlockDominators(bb);
	}

	// Compute the dominance frontier for each block.
	ComputeDomPostOrderTraversal(GetEntryBlock());
	PostOrderDOMIterator iter5(this);
	for (BasicBlock* bb = iter5.Next(); bb != NULL; bb = iter5.Next()) {
	ComputeDominanceFrontier(bb);
	}
	}

	/*
	* Perform dest U= src1 ^ ~src2
	* This is probably not general enough to be placed in BitVector.[ch].
	*/
	void MIRGraph::ComputeSuccLineIn(ArenaBitVector* dest, const ArenaBitVector* src1,
	const ArenaBitVector* src2) {
	if (dest->GetStorageSize() != src1->GetStorageSize() \|\|
	dest->GetStorageSize() != src2->GetStorageSize() \|\|
	dest->IsExpandable() != src1->IsExpandable() \|\|
	dest->IsExpandable() != src2->IsExpandable()) {
	LOG(FATAL) << "Incompatible set properties";
	}

	unsigned int idx;
	for (idx = 0; idx < dest->GetStorageSize(); idx++) {
	dest->GetRawStorage()[idx] \|= src1->GetRawStorageWord(idx) & ~(src2->GetRawStorageWord(idx));
	}
	}

	/*
	* Iterate through all successor blocks and propagate up the live-in sets.
	* The calculated result is used for phi-node pruning - where we only need to
	* insert a phi node if the variable is live-in to the block.
	*/
	bool MIRGraph::ComputeBlockLiveIns(BasicBlock* bb) {
	DCHECK_EQ(temp_bit_vector_size_, cu_->num_dalvik_registers);
	ArenaBitVector* temp_dalvik_register_v = temp_bit_vector_;

	if (bb->data_flow_info == NULL) {
	return false;
	}
	temp_dalvik_register_v->Copy(bb->data_flow_info->live_in_v);
	BasicBlock* bb_taken = GetBasicBlock(bb->taken);
	BasicBlock* bb_fall_through = GetBasicBlock(bb->fall_through);
	if (bb_taken && bb_taken->data_flow_info)
	ComputeSuccLineIn(temp_dalvik_register_v, bb_taken->data_flow_info->live_in_v,
	bb->data_flow_info->def_v);
	if (bb_fall_through && bb_fall_through->data_flow_info)
	ComputeSuccLineIn(temp_dalvik_register_v, bb_fall_through->data_flow_info->live_in_v,
	bb->data_flow_info->def_v);
	if (bb->successor_block_list_type != kNotUsed) {
	GrowableArray<SuccessorBlockInfo*>::Iterator iterator(bb->successor_blocks);
	while (true) {
	SuccessorBlockInfo *successor_block_info = iterator.Next();
	if (successor_block_info == NULL) {
	break;
	}
	BasicBlock* succ_bb = GetBasicBlock(successor_block_info->block);
	if (succ_bb->data_flow_info) {
	ComputeSuccLineIn(temp_dalvik_register_v, succ_bb->data_flow_info->live_in_v,
	bb->data_flow_info->def_v);
	}
	}
	}
	if (!temp_dalvik_register_v->Equal(bb->data_flow_info->live_in_v)) {
	bb->data_flow_info->live_in_v->Copy(temp_dalvik_register_v);
	return true;
	}
	return false;
	}

	/* Insert phi nodes to for each variable to the dominance frontiers */
	void MIRGraph::InsertPhiNodes() {
	int dalvik_reg;
	ArenaBitVector* phi_blocks = new (temp_scoped_alloc_.get()) ArenaBitVector(
	temp_scoped_alloc_.get(), GetNumBlocks(), false, kBitMapPhi);
	ArenaBitVector* input_blocks = new (temp_scoped_alloc_.get()) ArenaBitVector(
	temp_scoped_alloc_.get(), GetNumBlocks(), false, kBitMapInputBlocks);

	RepeatingPostOrderDfsIterator iter(this);
	bool change = false;
	for (BasicBlock* bb = iter.Next(false); bb != NULL; bb = iter.Next(change)) {
	change = ComputeBlockLiveIns(bb);
	}

	/* Iterate through each Dalvik register */
	for (dalvik_reg = cu_->num_dalvik_registers - 1; dalvik_reg >= 0; dalvik_reg--) {
	input_blocks->Copy(def_block_matrix_[dalvik_reg]);
	phi_blocks->ClearAllBits();
	do {
	// TUNING: When we repeat this, we could skip indexes from the previous pass.
	for (uint32_t idx : input_blocks->Indexes()) {
	BasicBlock* def_bb = GetBasicBlock(idx);
	if (def_bb->dom_frontier != nullptr) {
	phi_blocks->Union(def_bb->dom_frontier);
	}
	}
	} while (input_blocks->Union(phi_blocks));

	/*
	* Insert a phi node for dalvik_reg in the phi_blocks if the Dalvik
	* register is in the live-in set.
	*/
	for (uint32_t idx : phi_blocks->Indexes()) {
	BasicBlock* phi_bb = GetBasicBlock(idx);
	/* Variable will be clobbered before being used - no need for phi */
	if (!phi_bb->data_flow_info->live_in_v->IsBitSet(dalvik_reg)) {
	continue;
	}
	MIR *phi = NewMIR();
	phi->dalvikInsn.opcode = static_cast<Instruction::Code>(kMirOpPhi);
	phi->dalvikInsn.vA = dalvik_reg;
	phi->offset = phi_bb->start_offset;
	phi->m_unit_index = 0; // Arbitrarily assign all Phi nodes to outermost method.
	phi_bb->PrependMIR(phi);
	}
	}
	}

	/*
	* Worker function to insert phi-operands with latest SSA names from
	* predecessor blocks
	*/
	bool MIRGraph::InsertPhiNodeOperands(BasicBlock* bb) {
	/* Phi nodes are at the beginning of each block */
	for (MIR* mir = bb->first_mir_insn; mir != NULL; mir = mir->next) {
	if (mir->dalvikInsn.opcode != static_cast<Instruction::Code>(kMirOpPhi))
	return true;
	int ssa_reg = mir->ssa_rep->defs[0];
	DCHECK_GE(ssa_reg, 0); // Shouldn't see compiler temps here
	int v_reg = SRegToVReg(ssa_reg);

	/* Iterate through the predecessors */
	GrowableArray<BasicBlockId>::Iterator iter(bb->predecessors);
	size_t num_uses = bb->predecessors->Size();
	AllocateSSAUseData(mir, num_uses);
	int* uses = mir->ssa_rep->uses;
	BasicBlockId* incoming =
	static_cast<BasicBlockId>(arena_->Alloc(sizeof(BasicBlockId) num_uses,
	kArenaAllocDFInfo));
	mir->meta.phi_incoming = incoming;
	int idx = 0;
	while (true) {
	BasicBlock* pred_bb = GetBasicBlock(iter.Next());
	if (!pred_bb) {
	break;
	}
	int ssa_reg = pred_bb->data_flow_info->vreg_to_ssa_map_exit[v_reg];
	uses[idx] = ssa_reg;
	incoming[idx] = pred_bb->id;
	idx++;
	}
	}

	return true;
	}

	void MIRGraph::DoDFSPreOrderSSARename(BasicBlock* block) {
	if (block->visited \|\| block->hidden) {
	return;
	}
	block->visited = true;

	/* Process this block */
	DoSSAConversion(block);
	int map_size = sizeof(int) * cu_->num_dalvik_registers;

	/* Save SSA map snapshot */
	ScopedArenaAllocator allocator(&cu_->arena_stack);
	int* saved_ssa_map =
	static_cast<int*>(allocator.Alloc(map_size, kArenaAllocDalvikToSSAMap));
	memcpy(saved_ssa_map, vreg_to_ssa_map_, map_size);

	if (block->fall_through != NullBasicBlockId) {
	DoDFSPreOrderSSARename(GetBasicBlock(block->fall_through));
	/* Restore SSA map snapshot */
	memcpy(vreg_to_ssa_map_, saved_ssa_map, map_size);
	}
	if (block->taken != NullBasicBlockId) {
	DoDFSPreOrderSSARename(GetBasicBlock(block->taken));
	/* Restore SSA map snapshot */
	memcpy(vreg_to_ssa_map_, saved_ssa_map, map_size);
	}
	if (block->successor_block_list_type != kNotUsed) {
	GrowableArray<SuccessorBlockInfo*>::Iterator iterator(block->successor_blocks);
	while (true) {
	SuccessorBlockInfo *successor_block_info = iterator.Next();
	if (successor_block_info == NULL) {
	break;
	}
	BasicBlock* succ_bb = GetBasicBlock(successor_block_info->block);
	DoDFSPreOrderSSARename(succ_bb);
	/* Restore SSA map snapshot */
	memcpy(vreg_to_ssa_map_, saved_ssa_map, map_size);
	}
	}
	return;
	}

	} // namespace art