[turbofan] Gracefully bail out if OSR encounters a loop too deeply nested.

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/common-operator.h"
 #include "src/compiler/control-reducer.h"
 #include "src/compiler/frame.h"
 #include "src/compiler/graph.h"
 #include "src/compiler/js-graph.h"
+#include "src/compiler/loop-analysis.h"
 #include "src/compiler/node.h"
 #include "src/compiler/node-marker.h"
 #include "src/compiler/osr.h"
 #include "src/scopes.h"
 
 namespace v8 {
 namespace internal {
 namespace compiler {
 
 OsrHelper::OsrHelper(CompilationInfo* info)
     : parameter_count_(info->scope()->num_parameters()),
       stack_slot_count_(info->scope()->num_stack_slots()) {}
 
 
-void OsrHelper::Deconstruct(JSGraph* jsgraph, CommonOperatorBuilder* common,
+bool OsrHelper::Deconstruct(JSGraph* jsgraph, CommonOperatorBuilder* common,
                             Zone* tmp_zone) {
-  NodeDeque queue(tmp_zone);
   Graph* graph = jsgraph->graph();
-  NodeMarker<bool> marker(graph, 2);
-  queue.push_back(graph->end());
-  marker.Set(graph->end(), true);
+  Node* osr_normal_entry = nullptr;
+  Node* osr_loop_entry = nullptr;
+  Node* osr_loop = nullptr;
 
-  while (!queue.empty()) {
-    Node* node = queue.front();
-    queue.pop_front();
-
-    // Rewrite OSR-related nodes.
-    switch (node->opcode()) {
-      case IrOpcode::kOsrNormalEntry:
-        node->ReplaceUses(graph->NewNode(common->Dead()));
-        break;
-      case IrOpcode::kOsrLoopEntry:
-        node->ReplaceUses(graph->start());
-        break;
-      default:
-        break;
-    }
-    for (Node* const input : node->inputs()) {
-      if (!marker.Get(input)) {
-        marker.Set(input, true);
-        queue.push_back(input);
-      }
+  for (Node* node : graph->start()->uses()) {
+    if (node->opcode() == IrOpcode::kOsrLoopEntry) {
+      osr_loop_entry = node;  // found the OSR loop entry
+    } else if (node->opcode() == IrOpcode::kOsrNormalEntry) {
+      osr_normal_entry = node;
     }
   }
 
+  if (osr_loop_entry == nullptr) {
+    // No OSR entry found, do nothing.
+    CHECK_NE(nullptr, osr_normal_entry);
+    return true;
+  }
+
+  for (Node* use : osr_loop_entry->uses()) {
+    if (use->opcode() == IrOpcode::kLoop) {
+      CHECK_EQ(nullptr, osr_loop);  // should be only one OSR loop.
+      osr_loop = use;               // found the OSR loop.
+    }
+  }
+
+  CHECK_NE(nullptr, osr_loop);  // Should have found the OSR loop.
+
+  // Analyze the graph to determine how deeply nested the OSR loop is.
+  LoopTree* loop_tree = LoopFinder::BuildLoopTree(graph, tmp_zone);
+
+  LoopTree::Loop* loop = loop_tree->ContainingLoop(osr_loop);
+  if (loop->depth() > 0) return false;  // cannot OSR inner loops yet.
+
+  // TODO(titzer): perform loop peeling or graph duplication.
+
+  // 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(graph->NewNode(common->Dead()));
+  osr_loop_entry->ReplaceUses(graph->start());
   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());
 }
 
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8