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

R=jarin@chromium.org
BUG=

Review URL: https://codereview.chromium.org/877553007

Cr-Commit-Position: refs/heads/master@{#26318}

src/bailout-reason.h

@@ -332,6 +332,7 @@ namespace internal {
     "Wrong address or value passed to RecordWrite")                            \
   V(kShouldNotDirectlyEnterOsrFunction,                                        \
     "Should not directly enter OSR-compiled function")                         \
+  V(kOsrCompileFailed, "OSR compilation failed")                               \
   V(kYield, "Yield")
 
 

src/compiler/osr.cc

@@ -8,6 +8,7 @@
 #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"
@@ -22,38 +23,51 @@ OsrHelper::OsrHelper(CompilationInfo* info)
       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);
-
-  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;
+  Node* osr_normal_entry = nullptr;
+  Node* osr_loop_entry = nullptr;
+  Node* osr_loop = nullptr;
+
+  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;
     }
-    for (Node* const input : node->inputs()) {
-      if (!marker.Get(input)) {
-        marker.Set(input, true);
-        queue.push_back(input);
-      }
+  }
+
+  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;
 }
 
 

src/compiler/osr.h

@@ -99,7 +99,8 @@ class OsrHelper {
 
   // Deconstructs the artificial {OsrNormalEntry} and rewrites the graph so
   // that only the path corresponding to {OsrLoopEntry} remains.
-  void Deconstruct(JSGraph* jsgraph, CommonOperatorBuilder* common,
+  // Return {false} if the OSR deconstruction failed somehow.
+  bool Deconstruct(JSGraph* jsgraph, CommonOperatorBuilder* common,
                    Zone* tmp_zone);
 
   // Prepares the frame w.r.t. OSR.

src/compiler/pipeline.cc

@@ -414,7 +414,9 @@ struct OsrDeconstructionPhase {
     SourcePositionTable::Scope pos(data->source_positions(),
                                    SourcePosition::Unknown());
     OsrHelper osr_helper(data->info());
-    osr_helper.Deconstruct(data->jsgraph(), data->common(), temp_zone);
+    bool success =
+        osr_helper.Deconstruct(data->jsgraph(), data->common(), temp_zone);
+    if (!success) data->info()->RetryOptimization(kOsrCompileFailed);
   }
 };
 
@@ -774,8 +776,11 @@ void Pipeline::RunPrintAndVerify(const char* phase, bool untyped) {
 
 
 Handle<Code> Pipeline::GenerateCode() {
-  // TODO(turbofan): Make OSR work with inner loops and remove this bailout.
-  if (info()->is_osr() && !FLAG_turbo_osr) return Handle<Code>::null();
+  if (info()->is_osr() && !FLAG_turbo_osr) {
+    // TODO(turbofan): remove this flag and always handle OSR
+    info()->RetryOptimization(kOsrCompileFailed);
+    return Handle<Code>::null();
+  }
 
   // TODO(mstarzinger): This is just a temporary hack to make TurboFan work,
   // the correct solution is to restore the context register after invoking
@@ -863,6 +868,7 @@ Handle<Code> Pipeline::GenerateCode() {
 
     if (info()->is_osr()) {
       Run<OsrDeconstructionPhase>();
+      if (info()->bailout_reason() != kNoReason) return Handle<Code>::null();
       RunPrintAndVerify("OSR deconstruction");
     }
 
@@ -880,6 +886,7 @@ Handle<Code> Pipeline::GenerateCode() {
   } else {
     if (info()->is_osr()) {
       Run<OsrDeconstructionPhase>();
+      if (info()->bailout_reason() != kNoReason) return Handle<Code>::null();
       RunPrintAndVerify("OSR deconstruction");
     }
   }

test/mjsunit/compiler/osr-nested2.js

+// Copyright 2015 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.
+
+// Flags: --allow-natives-syntax --use-osr --turbo-osr
+
+function f() {
+  var sum = 0;
+  for (var i = 5; i < 6; i++) {
+    for (var j = 0; j < 1000000; j++) {
+      var x = i + 2;
+      var y = x + 5;
+      var z = y + 3;
+      sum += z;
+    }
+    if (true) break;
+  }
+  return sum;
+}
+
+
+assertEquals(15000000, f());
+assertEquals(15000000, f());
+assertEquals(15000000, f());

test/mjsunit/compiler/osr-nested3.js

+// Copyright 2015 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.
+
+// Flags: --allow-natives-syntax --use-osr --turbo-osr
+
+function f() {
+  var sum = 0;
+  for (var m = 99; m < 100; m++) {
+    for (var i = 5; i < 6; i++) {
+      for (var j = 0; j < 1000000; j++) {
+        var x = i + 2;
+        var y = x + 5;
+        var z = y + 3;
+        sum += z;
+      }
+      if (true) break;
+    }
+    if (true) break;
+  }
+  return sum;
+}
+
+
+assertEquals(15000000, f());
+assertEquals(15000000, f());
+assertEquals(15000000, f());