[turbofan] Fix handling of OsrLoopEntry in ControlReducer::ConnectNTL()

src/compiler/control-reducer.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/common-operator.h"
 #include "src/compiler/control-reducer.h"
 #include "src/compiler/graph.h"
 #include "src/compiler/graph-reducer.h"
 #include "src/compiler/js-graph.h"
 #include "src/compiler/node-marker.h"
@@ skipping 72 matching lines @@
     typedef std::pair<Node*, Node::UseEdges::iterator> FwIter;
     ZoneVector<FwIter> fw_stack(zone_);
     fw_stack.push_back(FwIter(start, start->use_edges().begin()));
 
     while (!fw_stack.empty()) {
       Node* node = fw_stack.back().first;
       TRACE("ControlFw: #%d:%s\n", node->id(), node->op()->mnemonic());
       bool pop = true;
       while (fw_stack.back().second != node->use_edges().end()) {
         Edge edge = *(fw_stack.back().second);
+        Node* succ = edge.from();
         if (NodeProperties::IsControlEdge(edge) &&
-            edge.from()->op()->ControlOutputCount() > 0) {
+            succ->op()->ControlOutputCount() > 0) {
           // Only walk control edges to control nodes.
-          Node* succ = edge.from();
-
           if (marked.IsOnStack(succ) && !marked.IsReachableFromEnd(succ)) {
             // {succ} is on stack and not reachable from end.
             Node* added = ConnectNTL(succ);
             nodes.push_back(added);
             marked.SetReachableFromEnd(added);
             AddBackwardsReachableNodes(marked, nodes, nodes.size() - 1);
 
             // Reset the use iterators for the entire stack.
             for (size_t i = 0; i < fw_stack.size(); i++) {
               FwIter& iter = fw_stack[i];
               fw_stack[i] = FwIter(iter.first, iter.first->use_edges().begin());
             }
             pop = false;  // restart traversing successors of this node.
             break;
           }
           if (!marked.IsReachableFromStart(succ)) {
             // {succ} is not yet reached from start.
-            marked.Push(succ);
             marked.SetReachableFromStart(succ);
-            fw_stack.push_back(FwIter(succ, succ->use_edges().begin()));
-            pop = false;  // "recurse" into successor control node.
-            break;
+            if (succ->opcode() != IrOpcode::kOsrLoopEntry) {
+              // Skip OsrLoopEntry; forms a confusing irredducible loop.
+              marked.Push(succ);
+              fw_stack.push_back(FwIter(succ, succ->use_edges().begin()));
+              pop = false;  // "recurse" into successor control node.
+              break;
+            }
           }
         }
         ++fw_stack.back().second;
       }
       if (pop) {
         marked.Pop(node);
         fw_stack.pop_back();
       }
     }
 
@@ skipping 462 matching lines @@
     case IrOpcode::kIfFalse:
       return impl.ReduceIfProjection(node, kFalse);
     default:
       return node;
   }
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8