[turbofan] Simply context specialization and fix for OSR.

src/compiler/osr.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/compiler.h"
 #include "src/compiler/all-nodes.h"
 #include "src/compiler/common-operator.h"
 #include "src/compiler/control-reducer.h"
 #include "src/compiler/frame.h"
 #include "src/compiler/graph.h"
@@ skipping 85 matching lines @@
     }
 
     // Construct the transfer from the previous graph copies to the new copy.
     Node* loop_header = loop_tree->HeaderNode(loop);
     NodeVector* previous =
         copies.size() > 1 ? copies[copies.size() - 2] : nullptr;
     const int backedges = loop_header->op()->ControlInputCount() - 1;
     if (backedges == 1) {
       // Simple case. Map the incoming edges to the loop to the previous copy.
       for (Node* node : loop_tree->HeaderNodes(loop)) {
+        if (!all.IsLive(node)) continue;  // dead phi hanging off loop.
         Node* copy = mapping->at(node->id());
         Node* backedge = node->InputAt(1);
         if (previous) backedge = previous->at(backedge->id());
         copy->ReplaceInput(0, backedge);
       }
     } else {
       // Complex case. Multiple backedges. Introduce a merge for incoming edges.
       tmp_inputs.clear();
       for (int i = 0; i < backedges; i++) {
         Node* backedge = loop_header->InputAt(i + 1);
         if (previous) backedge = previous->at(backedge->id());
         tmp_inputs.push_back(backedge);
       }
       Node* merge =
           graph->NewNode(common->Merge(backedges), backedges, &tmp_inputs[0]);
       for (Node* node : loop_tree->HeaderNodes(loop)) {
+        if (!all.IsLive(node)) continue;  // dead phi hanging off loop.
         Node* copy = mapping->at(node->id());
         if (node == loop_header) {
           // The entry to the loop is the merge.
           copy->ReplaceInput(0, merge);
         } else {
           // Merge inputs to the phi at the loop entry.
           tmp_inputs.clear();
           for (int i = 0; i < backedges; i++) {
             Node* backedge = node->InputAt(i + 1);
             if (previous) backedge = previous->at(backedge->id());
@@ skipping 75 matching lines @@
   Node* dead = jsgraph->DeadControl();
   LoopTree::Loop* loop = loop_tree->ContainingLoop(osr_loop);
   if (loop->depth() > 0) {
     PeelOuterLoopsForOsr(graph, common, tmp_zone, dead, loop_tree, loop,
                          osr_normal_entry, osr_loop_entry);
   }
 
   // Replace the normal entry with {Dead} and the loop entry with {Start}
   // and run the control reducer to clean up the graph.
   osr_normal_entry->ReplaceUses(dead);
+  osr_normal_entry->Kill();
   osr_loop_entry->ReplaceUses(graph->start());
+  osr_loop_entry->Kill();
 
   // Normally the control reducer removes loops whose first input is dead,
   // but we need to avoid that because the osr_loop is reachable through
   // the second input, so reduce it and its phis manually.
   osr_loop->ReplaceInput(0, dead);
   Node* node = ControlReducer::ReduceMerge(jsgraph, common, osr_loop);
   if (node != osr_loop) osr_loop->ReplaceUses(node);
 
   // Run the normal control reduction, which naturally trims away the dead
   // parts of the graph.
   ControlReducer::ReduceGraph(tmp_zone, jsgraph, common);
 
   return true;
 }
 
 
 void OsrHelper::SetupFrame(Frame* frame) {
   // The optimized frame will subsume the unoptimized frame. Do so by reserving
   // the first spill slots.
   frame->ReserveSpillSlots(UnoptimizedFrameSlots());
   // The frame needs to be adjusted by the number of unoptimized frame slots.
   frame->SetOsrStackSlotCount(static_cast<int>(UnoptimizedFrameSlots()));
 }
 
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8