slight HGraph::CreateGraph refactor

src/hydrogen.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 718 matching lines @@
          order->Contains(block->end()->SecondSuccessor()) ||
          block->end()->SecondSuccessor()->IsLoopHeader());
   order->Add(block);
 }
 
 
 void HGraph::AssignDominators() {
   HPhase phase("Assign dominators", this);
   for (int i = 0; i < blocks_.length(); ++i) {
     if (blocks_[i]->IsLoopHeader()) {
+      // Only the first predecessor of a loop header is from outside the loop.
+      // All others are back edges, and thus cannot dominate the loop header.
       blocks_[i]->AssignCommonDominator(blocks_[i]->predecessors()->first());
     } else {
       for (int j = 0; j < blocks_[i]->predecessors()->length(); ++j) {
         blocks_[i]->AssignCommonDominator(blocks_[i]->predecessors()->at(j));
       }
     }
   }
+}
 
-  // Propagate flag marking blocks containing unconditional deoptimize.
+// Mark all blocks that are dominated by an unconditional soft deoptimize to
+// prevent code motion across those blocks.
+void HGraph::PropagateDeoptimizingMark()
+{
+  HPhase phase("Propagate deoptimizing mark", this);
   MarkAsDeoptimizingRecursively(entry_block());
 }
 
-
-// Mark all blocks that are dominated by an unconditional deoptimize.
 void HGraph::MarkAsDeoptimizingRecursively(HBasicBlock* block) {
   for (int i = 0; i < block->dominated_blocks()->length(); ++i) {
     HBasicBlock* dominated = block->dominated_blocks()->at(i);
     if (block->IsDeoptimizing()) dominated->MarkAsDeoptimizing();
     MarkAsDeoptimizingRecursively(dominated);
   }
 }
 
 void HGraph::EliminateRedundantPhis() {
   HPhase phase("Redundant phi elimination", this);
@@ skipping 1525 matching lines @@
 
     if (current_block() != NULL) {
       HReturn* instr = new(zone()) HReturn(graph()->GetConstantUndefined());
       current_block()->FinishExit(instr);
       set_current_block(NULL);
     }
   }
 
   graph()->OrderBlocks();
   graph()->AssignDominators();
+  graph()->PropagateDeoptimizingMark();
   graph()->EliminateRedundantPhis();
   if (FLAG_eliminate_dead_phis) graph()->EliminateUnreachablePhis();
   if (!graph()->CollectPhis()) {
     Bailout("Unsupported phi-use");
     return NULL;
   }
 
   HInferRepresentation rep(graph());
   rep.Analyze();
 
@@ skipping 4418 matching lines @@
     }
   }
 
 #ifdef DEBUG
   if (graph_ != NULL) graph_->Verify();
   if (allocator_ != NULL) allocator_->Verify();
 #endif
 }
 
 } }  // namespace v8::internal