Refactored FlowGraphBuilder into a separate FlowGraph representation.

runtime/vm/flow_graph_builder.cc

Index: runtime/vm/flow_graph_builder.cc
diff --git a/runtime/vm/flow_graph_builder.cc b/runtime/vm/flow_graph_builder.cc
index 3cf0ae006179539c3cc2c3c8ff511d201f815bf3..838ece3a777da4f3415cbd310ea34f4c6c69544b 100644
--- a/runtime/vm/flow_graph_builder.cc
+++ b/runtime/vm/flow_graph_builder.cc
@@ -5,7 +5,6 @@
 #include "vm/flow_graph_builder.h"
 
 #include "vm/ast_printer.h"
-#include "vm/bit_vector.h"
 #include "vm/code_descriptors.h"
 #include "vm/dart_entry.h"
 #include "vm/flags.h"
@@ -39,13 +38,10 @@ FlowGraphBuilder::FlowGraphBuilder(const ParsedFunction& parsed_function)
         ? parsed_function.function().num_fixed_parameters()
         : 0),
     stack_local_count_(parsed_function.stack_local_count()),
-    preorder_block_entries_(),
-    postorder_block_entries_(),
     context_level_(0),
     last_used_try_index_(CatchClauseNode::kInvalidTryIndex),
     try_index_(CatchClauseNode::kInvalidTryIndex),
-    graph_entry_(NULL),
-    current_ssa_temp_index_(0) { }
+    graph_entry_(NULL) { }
 
 
 void FlowGraphBuilder::AddCatchEntry(TargetEntryInstr* entry) {
@@ -2389,7 +2385,7 @@ void EffectGraphVisitor::VisitInlinedFinallyNode(InlinedFinallyNode* node) {
 }
 
 
-void FlowGraphBuilder::BuildGraph(bool for_optimized, bool use_ssa) {
+FlowGraph* FlowGraphBuilder::BuildGraph() {
   if (FLAG_print_ast) {
     // Print the function ast before IL generation.
     AstPrinter::PrintFunctionNodes(parsed_function());
@@ -2407,440 +2403,10 @@ void FlowGraphBuilder::BuildGraph(bool for_optimized, bool use_ssa) {
   AppendFragment(normal_entry, for_effect);
   // Check that the graph is properly terminated.
   ASSERT(!for_effect.is_open());
-  GrowableArray<intptr_t> parent;
-  GrowableArray<BitVector*> assigned_vars;
-
-  // Perform a depth-first traversal of the graph to build preorder and
-  // postorder block orders.
-  graph_entry_->DiscoverBlocks(NULL,  // Entry block predecessor.
-                               &preorder_block_entries_,
-                               &postorder_block_entries_,
-                               &parent,
-                               &assigned_vars,
-                               variable_count(),
-                               non_copied_parameter_count_);
-  // Number blocks in reverse postorder.
-  intptr_t block_count = postorder_block_entries_.length();
-  for (intptr_t i = 0; i < block_count; ++i) {
-    postorder_block_entries_[i]->set_block_id(block_count - i - 1);
-  }
-
-  if (for_optimized) {
-    // Link instructions backwards for optimized compilation.
-    for (intptr_t i = 0; i < block_count; ++i) {
-      BlockEntryInstr* entry = postorder_block_entries_[i];
-      Instruction* previous = entry;
-      for (ForwardInstructionIterator it(entry); !it.Done(); it.Advance()) {
-        Instruction* current = it.Current();
-        current->set_previous(previous);
-        previous = current;
-      }
-    }
-  }
-
-  if (for_optimized && use_ssa) {
-    GrowableArray<BitVector*> dominance_frontier;
-    ComputeDominators(&preorder_block_entries_, &parent, &dominance_frontier);
-    InsertPhis(preorder_block_entries_,
-               assigned_vars,
-               dominance_frontier);
-
-    GrowableArray<PhiInstr*> live_phis;
-
-    // Rename uses to reference inserted phis where appropriate.
-    // Collect phis that reach a non-environment use.
-    Rename(&live_phis);
-
-    // Propagate alive mark transitively from alive phis.
-    MarkLivePhis(&live_phis);
-  }
-  if (FLAG_print_flow_graph || (Dart::flow_graph_writer() != NULL)) {
-    intptr_t length = postorder_block_entries_.length();
-    GrowableArray<BlockEntryInstr*> reverse_postorder(length);
-    for (intptr_t i = length - 1; i >= 0; --i) {
-      reverse_postorder.Add(postorder_block_entries_[i]);
-    }
-    if (FLAG_print_flow_graph) {
-      // Print flow graph to stdout.
-      FlowGraphPrinter printer(function, reverse_postorder);
-      printer.PrintBlocks();
-    }
-    if (Dart::flow_graph_writer() != NULL) {
-      // Write flow graph to file.
-      FlowGraphVisualizer printer(function, reverse_postorder);
-      printer.PrintFunction();
-    }
-  }
-}
-
-
-// Compute immediate dominators and the dominance frontier for each basic
-// block.  As a side effect of the algorithm, sets the immediate dominator
-// of each basic block.
-//
-// preorder: an input list of basic block entries in preorder.  The
-//     algorithm relies on the block ordering.
-//
-// parent: an input parameter encoding a depth-first spanning tree of
-//     the control flow graph.  The array maps the preorder block
-//     number of a block to the preorder block number of its spanning
-//     tree parent.
-//
-// dominance_frontier: an output parameter encoding the dominance frontier.
-//     The array maps the preorder block number of a block to the set of
-//     (preorder block numbers of) blocks in the dominance frontier.
-void FlowGraphBuilder::ComputeDominators(
-    GrowableArray<BlockEntryInstr*>* preorder,
-    GrowableArray<intptr_t>* parent,
-    GrowableArray<BitVector*>* dominance_frontier) {
-  // Use the SEMI-NCA algorithm to compute dominators.  This is a two-pass
-  // version of the Lengauer-Tarjan algorithm (LT is normally three passes)
-  // that eliminates a pass by using nearest-common ancestor (NCA) to
-  // compute immediate dominators from semidominators.  It also removes a
-  // level of indirection in the link-eval forest data structure.
-  //
-  // The algorithm is described in Georgiadis, Tarjan, and Werneck's
-  // "Finding Dominators in Practice".
-  // See http://www.cs.princeton.edu/~rwerneck/dominators/ .
-
-  // All arrays are maps between preorder basic-block numbers.
-  intptr_t size = parent->length();
-  GrowableArray<intptr_t> idom(size);  // Immediate dominator.
-  GrowableArray<intptr_t> semi(size);  // Semidominator.
-  GrowableArray<intptr_t> label(size);  // Label for link-eval forest.
-
-  // 1. First pass: compute semidominators as in Lengauer-Tarjan.
-  // Semidominators are computed from a depth-first spanning tree and are an
-  // approximation of immediate dominators.
-
-  // Use a link-eval data structure with path compression.  Implement path
-  // compression in place by mutating the parent array.  Each block has a
-  // label, which is the minimum block number on the compressed path.
-
-  // Initialize idom, semi, and label used by SEMI-NCA.  Initialize the
-  // dominance frontier output array.
-  for (intptr_t i = 0; i < size; ++i) {
-    idom.Add((*parent)[i]);
-    semi.Add(i);
-    label.Add(i);
-    dominance_frontier->Add(new BitVector(size));
-  }
-
-  // Loop over the blocks in reverse preorder (not including the graph
-  // entry).
-  for (intptr_t block_index = size - 1; block_index >= 1; --block_index) {
-    // Loop over the predecessors.
-    BlockEntryInstr* block = (*preorder)[block_index];
-    for (intptr_t i = 0, count = block->PredecessorCount(); i < count; ++i) {
-      BlockEntryInstr* pred = block->PredecessorAt(i);
-      ASSERT(pred != NULL);
-
-      // Look for the semidominator by ascending the semidominator path
-      // starting from pred.
-      intptr_t pred_index = pred->preorder_number();
-      intptr_t best = pred_index;
-      if (pred_index > block_index) {
-        CompressPath(block_index, pred_index, parent, &label);
-        best = label[pred_index];
-      }
-
-      // Update the semidominator if we've found a better one.
-      semi[block_index] = Utils::Minimum(semi[block_index], semi[best]);
-    }
-
-    // Now use label for the semidominator.
-    label[block_index] = semi[block_index];
-  }
-
-  // 2. Compute the immediate dominators as the nearest common ancestor of
-  // spanning tree parent and semidominator, for all blocks except the entry.
-  for (intptr_t block_index = 1; block_index < size; ++block_index) {
-    intptr_t dom_index = idom[block_index];
-    while (dom_index > semi[block_index]) {
-      dom_index = idom[dom_index];
-    }
-    idom[block_index] = dom_index;
-    (*preorder)[block_index]->set_dominator((*preorder)[dom_index]);
-    (*preorder)[dom_index]->AddDominatedBlock((*preorder)[block_index]);
-  }
-
-  // 3. Now compute the dominance frontier for all blocks.  This is
-  // algorithm in "A Simple, Fast Dominance Algorithm" (Figure 5), which is
-  // attributed to a paper by Ferrante et al.  There is no bookkeeping
-  // required to avoid adding a block twice to the same block's dominance
-  // frontier because we use a set to represent the dominance frontier.
-  for (intptr_t block_index = 0; block_index < size; ++block_index) {
-    BlockEntryInstr* block = (*preorder)[block_index];
-    intptr_t count = block->PredecessorCount();
-    if (count <= 1) continue;
-    for (intptr_t i = 0; i < count; ++i) {
-      BlockEntryInstr* runner = block->PredecessorAt(i);
-      while (runner != block->dominator()) {
-        (*dominance_frontier)[runner->preorder_number()]->Add(block_index);
-        runner = runner->dominator();
-      }
-    }
-  }
-}
-
-
-void FlowGraphBuilder::CompressPath(intptr_t start_index,
-                                    intptr_t current_index,
-                                    GrowableArray<intptr_t>* parent,
-                                    GrowableArray<intptr_t>* label) {
-  intptr_t next_index = (*parent)[current_index];
-  if (next_index > start_index) {
-    CompressPath(start_index, next_index, parent, label);
-    (*label)[current_index] =
-        Utils::Minimum((*label)[current_index], (*label)[next_index]);
-    (*parent)[current_index] = (*parent)[next_index];
-  }
-}
-
-
-void FlowGraphBuilder::InsertPhis(
-    const GrowableArray<BlockEntryInstr*>& preorder,
-    const GrowableArray<BitVector*>& assigned_vars,
-    const GrowableArray<BitVector*>& dom_frontier) {
-  const intptr_t block_count = preorder.length();
-  // Map preorder block number to the highest variable index that has a phi
-  // in that block.  Use it to avoid inserting multiple phis for the same
-  // variable.
-  GrowableArray<intptr_t> has_already(block_count);
-  // Map preorder block number to the highest variable index for which the
-  // block went on the worklist.  Use it to avoid adding the same block to
-  // the worklist more than once for the same variable.
-  GrowableArray<intptr_t> work(block_count);
-
-  // Initialize has_already and work.
-  for (intptr_t block_index = 0; block_index < block_count; ++block_index) {
-    has_already.Add(-1);
-    work.Add(-1);
-  }
-
-  // Insert phis for each variable in turn.
-  GrowableArray<BlockEntryInstr*> worklist;
-  for (intptr_t var_index = 0; var_index < variable_count(); ++var_index) {
-    // Add to the worklist each block containing an assignment.
-    for (intptr_t block_index = 0; block_index < block_count; ++block_index) {
-      if (assigned_vars[block_index]->Contains(var_index)) {
-        work[block_index] = var_index;
-        worklist.Add(preorder[block_index]);
-      }
-    }
-
-    while (!worklist.is_empty()) {
-      BlockEntryInstr* current = worklist.Last();
-      worklist.RemoveLast();
-      // Ensure a phi for each block in the dominance frontier of current.
-      for (BitVector::Iterator it(dom_frontier[current->preorder_number()]);
-           !it.Done();
-           it.Advance()) {
-        int index = it.Current();
-        if (has_already[index] < var_index) {
-          BlockEntryInstr* block = preorder[index];
-          ASSERT(block->IsJoinEntry());
-          block->AsJoinEntry()->InsertPhi(var_index, variable_count());
-          has_already[index] = var_index;
-          if (work[index] < var_index) {
-            work[index] = var_index;
-            worklist.Add(block);
-          }
-        }
-      }
-    }
-  }
+  return new FlowGraph(*this, graph_entry_);
 }
 
 
-void FlowGraphBuilder::Rename(GrowableArray<PhiInstr*>* live_phis) {
-  // TODO(fschneider): Support catch-entry.
-  if (graph_entry_->SuccessorCount() > 1) {
-    Bailout("Catch-entry support in SSA.");
-  }
-
-  // Initialize start environment.
-  GrowableArray<Value*> start_env(variable_count());
-  for (intptr_t i = 0; i < parameter_count(); ++i) {
-    ParameterInstr* param = new ParameterInstr(i);
-    param->set_ssa_temp_index(alloc_ssa_temp_index());  // New SSA temp.
-    start_env.Add(new UseVal(param));
-  }
-
-  // All locals are initialized with #null.
-  Value* null_value = new ConstantVal(Object::ZoneHandle());
-  while (start_env.length() < variable_count()) {
-    start_env.Add(null_value);
-  }
-  graph_entry_->set_start_env(
-      new Environment(start_env, non_copied_parameter_count_));
-
-  BlockEntryInstr* normal_entry = graph_entry_->SuccessorAt(0);
-  ASSERT(normal_entry != NULL);  // Must have entry.
-  GrowableArray<Value*> env(variable_count());
-  env.AddArray(start_env);
-  RenameRecursive(normal_entry, &env, live_phis);
-}
-
-
-// Helper to a copy a value iff it is a UseVal.
-static Value* CopyValue(Value* value) {
-  return value->IsUse()
-      ? new UseVal(value->AsUse()->definition())
-      : value;
-}
-
-
-void FlowGraphBuilder::RenameRecursive(BlockEntryInstr* block_entry,
-                                       GrowableArray<Value*>* env,
-                                       GrowableArray<PhiInstr*>* live_phis) {
-  // 1. Process phis first.
-  if (block_entry->IsJoinEntry()) {
-    JoinEntryInstr* join = block_entry->AsJoinEntry();
-    if (join->phis() != NULL) {
-      for (intptr_t i = 0; i < join->phis()->length(); ++i) {
-        PhiInstr* phi = (*join->phis())[i];
-        if (phi != NULL) {
-          (*env)[i] = new UseVal(phi);
-          phi->set_ssa_temp_index(alloc_ssa_temp_index());  // New SSA temp.
-        }
-      }
-    }
-  }
-
-  // 2. Process normal instructions.
-  for (ForwardInstructionIterator it(block_entry); !it.Done(); it.Advance()) {
-    Instruction* current = it.Current();
-    // Attach current environment to the instruction. First, each instruction
-    // gets a full copy of the environment. Later we optimize this by
-    // eliminating unnecessary environments.
-    current->set_env(new Environment(*env, non_copied_parameter_count_));
-
-    // 2a. Handle uses:
-    // Update expression stack environment for each use.
-    // For each use of a LoadLocal or StoreLocal: Replace it with the value
-    // from the environment.
-    for (intptr_t i = current->InputCount() - 1; i >= 0; --i) {
-      Value* v = current->InputAt(i);
-      if (!v->IsUse()) continue;
-      // Update expression stack.
-      ASSERT(env->length() > variable_count());
-
-      Value* input_value = env->Last();
-      ASSERT(input_value->IsUse());
-      env->RemoveLast();
-
-      BindInstr* as_bind = v->AsUse()->definition()->AsBind();
-      if ((as_bind != NULL) &&
-          (as_bind->computation()->IsLoadLocal() ||
-           as_bind->computation()->IsStoreLocal())) {
-        current->SetInputAt(i, CopyValue(input_value));
-      }
-    }
-
-    // Drop pushed arguments for calls.
-    for (intptr_t j = 0; j < current->ArgumentCount(); j++) {
-      env->RemoveLast();
-    }
-
-    // 2b. Handle LoadLocal and StoreLocal.
-    // For each LoadLocal: Remove it from the graph.
-    // For each StoreLocal: Remove it from the graph and update the environment.
-    BindInstr* bind = current->AsBind();
-    if (bind != NULL) {
-      LoadLocalComp* load = bind->computation()->AsLoadLocal();
-      StoreLocalComp* store = bind->computation()->AsStoreLocal();
-      if ((load != NULL) || (store != NULL)) {
-        intptr_t index;
-        if (store != NULL) {
-          index = store->local().BitIndexIn(non_copied_parameter_count_);
-          // Update renaming environment.
-          (*env)[index] = store->value();
-        } else {
-          // The graph construction ensures we do not have an unused LoadLocal
-          // computation.
-          ASSERT(bind->is_used());
-          index = load->local().BitIndexIn(non_copied_parameter_count_);
-
-          Value* value = (*env)[index];
-          if (value->IsUse()) {
-            PhiInstr* phi = value->AsUse()->definition()->AsPhi();
-            if ((phi != NULL) && !phi->is_alive()) {
-              phi->mark_alive();
-              live_phis->Add(phi);
-            }
-          }
-        }
-        // Update expression stack and remove from graph.
-        if (bind->is_used()) {
-          env->Add(CopyValue((*env)[index]));
-        }
-        it.RemoveCurrentFromGraph();
-      } else {
-        // Not a load or store.
-        if (bind->is_used()) {
-          // Assign fresh SSA temporary and update expression stack.
-          bind->set_ssa_temp_index(alloc_ssa_temp_index());
-          env->Add(new UseVal(bind));
-        }
-      }
-    }
-
-    // 2c. Handle pushed argument.
-    PushArgumentInstr* push = current->AsPushArgument();
-    if (push != NULL) {
-      env->Add(new UseVal(push));
-    }
-  }
-
-  // 3. Process dominated blocks.
-  for (intptr_t i = 0; i < block_entry->dominated_blocks().length(); ++i) {
-    BlockEntryInstr* block = block_entry->dominated_blocks()[i];
-    GrowableArray<Value*> new_env(env->length());
-    new_env.AddArray(*env);
-    RenameRecursive(block, &new_env, live_phis);
-  }
-
-  // 4. Process successor block. We have edge-split form, so that only blocks
-  // with one successor can have a join block as successor.
-  if ((block_entry->last_instruction()->SuccessorCount() == 1) &&
-      block_entry->last_instruction()->SuccessorAt(0)->IsJoinEntry()) {
-    JoinEntryInstr* successor =
-        block_entry->last_instruction()->SuccessorAt(0)->AsJoinEntry();
-    intptr_t pred_index = successor->IndexOfPredecessor(block_entry);
-    ASSERT(pred_index >= 0);
-    if (successor->phis() != NULL) {
-      for (intptr_t i = 0; i < successor->phis()->length(); ++i) {
-        PhiInstr* phi = (*successor->phis())[i];
-        if (phi != NULL) {
-          // Rename input operand and make a copy if it is a UseVal.
-          Value* new_val = (*env)[i]->IsUse()
-              ? new UseVal((*env)[i]->AsUse()->definition())
-              : (*env)[i];
-          phi->SetInputAt(pred_index, new_val);
-        }
-      }
-    }
-  }
-}
-
-
-void FlowGraphBuilder::MarkLivePhis(GrowableArray<PhiInstr*>* live_phis) {
-  while (!live_phis->is_empty()) {
-    PhiInstr* phi = live_phis->Last();
-    live_phis->RemoveLast();
-    for (intptr_t i = 0; i < phi->InputCount(); i++) {
-      Value* val = phi->InputAt(i);
-      if (!val->IsUse()) continue;
-      PhiInstr* used_phi = val->AsUse()->definition()->AsPhi();
-      if ((used_phi != NULL) && !used_phi->is_alive()) {
-        used_phi->mark_alive();
-        live_phis->Add(used_phi);
-      }
-    }
-  }
-}
-
 void FlowGraphBuilder::Bailout(const char* reason) {
   const char* kFormat = "FlowGraphBuilder Bailout: %s %s";
   const char* function_name = parsed_function_.function().ToCString();