[Turbofan] Enable reducers to report their name to make reducer tracing clearer

Each reducer now has a virtual reducer_name function, returning its name
(the name of the class containing this reducer). This gets displayed when
using the --trace_turbo_reduction flag. Also when using this flags more
messages are displayed.

Actually when a node is replaced in-place (which is called an update
of the node), other reducers can still update it right after the
in-place replacement. When a node is really replaced (not in-place),
then we stop trying to apply reducers to it before we propagate the
reduction through the relevant nodes.

Before a message got printed only for the last reduction it went
through. So in case a node was reduced in-place several times
in a row, only the last update was printed, or none at all if after
being reduced in-place it got reduced by being replaced by another
node: only the non-in-place replacement was showed. 

Now each time an in-place reduction is applied to a node, a message
gets printed.

Bug: 
Change-Id: Id0f816fecd44c01d0253966c6decc4861be0c2fa
Reviewed-on: https://chromium-review.googlesource.com/563365Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Alexandre Talon <alexandret@google.com>
Cr-Commit-Position: refs/heads/master@{#46552}

src/compiler/branch-elimination.h

@@ -23,6 +23,8 @@ class V8_EXPORT_PRIVATE BranchElimination final
   BranchElimination(Editor* editor, JSGraph* js_graph, Zone* zone);
   ~BranchElimination() final;
 
+  const char* reducer_name() const override { return "BranchElimination"; }
+
   Reduction Reduce(Node* node) final;
 
  private:

src/compiler/check-elimination.h

@@ -24,6 +24,8 @@ class V8_EXPORT_PRIVATE CheckElimination final
       : AdvancedReducer(editor), jsgraph_(jsgraph) {}
   ~CheckElimination() final {}
 
+  const char* reducer_name() const override { return "CheckElimination"; }
+
   Reduction Reduce(Node* node) final;
 
  private:

src/compiler/checkpoint-elimination.h

@@ -20,6 +20,8 @@ class V8_EXPORT_PRIVATE CheckpointElimination final
   explicit CheckpointElimination(Editor* editor);
   ~CheckpointElimination() final {}
 
+  const char* reducer_name() const override { return "CheckpointElimination"; }
+
   Reduction Reduce(Node* node) final;
 
  private:

src/compiler/common-operator-reducer.h

@@ -29,6 +29,8 @@ class V8_EXPORT_PRIVATE CommonOperatorReducer final
                         MachineOperatorBuilder* machine);
   ~CommonOperatorReducer() final {}
 
+  const char* reducer_name() const override { return "CommonOperatorReducer"; }
+
   Reduction Reduce(Node* node) final;
 
  private:

src/compiler/dead-code-elimination.h

@@ -28,6 +28,8 @@ class V8_EXPORT_PRIVATE DeadCodeElimination final
                       CommonOperatorBuilder* common);
   ~DeadCodeElimination() final {}
 
+  const char* reducer_name() const override { return "DeadCodeElimination"; }
+
   Reduction Reduce(Node* node) final;
 
  private:

src/compiler/escape-analysis-reducer.h

@@ -24,6 +24,8 @@ class V8_EXPORT_PRIVATE EscapeAnalysisReducer final
   EscapeAnalysisReducer(Editor* editor, JSGraph* jsgraph,
                         EscapeAnalysis* escape_analysis, Zone* zone);
 
+  const char* reducer_name() const override { return "EscapeAnalysisReducer"; }
+
   Reduction Reduce(Node* node) final;
 
   void Finalize() override;

src/compiler/graph-reducer.cc

@@ -89,11 +89,22 @@ Reduction GraphReducer::Reduce(Node* const node) {
         // {replacement} == {node} represents an in-place reduction. Rerun
         // all the other reducers for this node, as now there may be more
         // opportunities for reduction.
+        if (FLAG_trace_turbo_reduction) {
+          OFStream os(stdout);
+          os << "- In-place update of " << *node << " by reducer "
+             << (*i)->reducer_name() << std::endl;
+        }
         skip = i;
         i = reducers_.begin();
         continue;
       } else {
         // {node} was replaced by another node.
+        if (FLAG_trace_turbo_reduction) {
+          OFStream os(stdout);
+          os << "- Replacement of " << *node << " with "
+             << *(reduction.replacement()) << " by reducer "
+             << (*i)->reducer_name() << std::endl;
+        }
         return reduction;
       }
     }
@@ -146,10 +157,6 @@ void GraphReducer::ReduceTop() {
   // Check if the reduction is an in-place update of the {node}.
   Node* const replacement = reduction.replacement();
   if (replacement == node) {
-    if (FLAG_trace_turbo_reduction) {
-      OFStream os(stdout);
-      os << "- In-place update of " << *replacement << std::endl;
-    }
     // In-place update of {node}, may need to recurse on an input.
     Node::Inputs node_inputs = node->inputs();
     for (int i = 0; i < node_inputs.count(); ++i) {
@@ -183,10 +190,6 @@ void GraphReducer::Replace(Node* node, Node* replacement) {
 
 
 void GraphReducer::Replace(Node* node, Node* replacement, NodeId max_id) {
-  if (FLAG_trace_turbo_reduction) {
-    OFStream os(stdout);
-    os << "- Replacing " << *node << " with " << *replacement << std::endl;
-  }
   if (node == graph()->start()) graph()->SetStart(replacement);
   if (node == graph()->end()) graph()->SetEnd(replacement);
   if (replacement->id() <= max_id) {

src/compiler/graph-reducer.h

@@ -46,6 +46,9 @@ class V8_EXPORT_PRIVATE Reducer {
  public:
   virtual ~Reducer() {}
 
+  // Only used for tracing, when using the --trace_turbo_reduction flag.
+  virtual const char* reducer_name() const = 0;
+
   // Try to reduce a node if possible.
   virtual Reduction Reduce(Node* node) = 0;
 

src/compiler/js-builtin-reducer.h

@@ -42,6 +42,8 @@ class V8_EXPORT_PRIVATE JSBuiltinReducer final
                    Handle<Context> native_context);
   ~JSBuiltinReducer() final {}
 
+  const char* reducer_name() const override { return "JSBuiltinReducer"; }
+
   Reduction Reduce(Node* node) final;
 
  private:

src/compiler/js-call-reducer.h

@@ -42,6 +42,8 @@ class JSCallReducer final : public AdvancedReducer {
         native_context_(native_context),
         dependencies_(dependencies) {}
 
+  const char* reducer_name() const override { return "JSCallReducer"; }
+
   Reduction Reduce(Node* node) final;
 
   // Processes the waitlist gathered while the reducer was running,

src/compiler/js-context-specialization.h

@@ -40,6 +40,10 @@ class JSContextSpecialization final : public AdvancedReducer {
         outer_(outer),
         closure_(closure) {}
 
+  const char* reducer_name() const override {
+    return "JSContextSpecialization";
+  }
+
   Reduction Reduce(Node* node) final;
 
  private:

src/compiler/js-create-lowering.h

@@ -44,6 +44,8 @@ class V8_EXPORT_PRIVATE JSCreateLowering final
         zone_(zone) {}
   ~JSCreateLowering() final {}
 
+  const char* reducer_name() const override { return "JSCreateLowering"; }
+
   Reduction Reduce(Node* node) final;
 
  private:

src/compiler/js-frame-specialization.h

@@ -25,6 +25,8 @@ class JSFrameSpecialization final : public AdvancedReducer {
       : AdvancedReducer(editor), frame_(frame), jsgraph_(jsgraph) {}
   ~JSFrameSpecialization() final {}
 
+  const char* reducer_name() const override { return "JSFrameSpecialization"; }
+
   Reduction Reduce(Node* node) final;
 
  private:

src/compiler/js-generic-lowering.h

@@ -27,6 +27,8 @@ class JSGenericLowering final : public Reducer {
   explicit JSGenericLowering(JSGraph* jsgraph);
   ~JSGenericLowering() final;
 
+  const char* reducer_name() const override { return "JSGenericLowering"; }
+
   Reduction Reduce(Node* node) final;
 
  protected:

src/compiler/js-inlining-heuristic.h

@@ -24,6 +24,8 @@ class JSInliningHeuristic final : public AdvancedReducer {
         seen_(local_zone),
         jsgraph_(jsgraph) {}
 
+  const char* reducer_name() const override { return "JSInliningHeuristic"; }
+
   Reduction Reduce(Node* node) final;
 
   // Processes the list of candidates gathered while the reducer was running,

src/compiler/js-inlining.h

@@ -31,6 +31,8 @@ class JSInliner final : public AdvancedReducer {
         jsgraph_(jsgraph),
         source_positions_(source_positions) {}
 
+  const char* reducer_name() const override { return "JSInliner"; }
+
   // Reducer interface, eagerly inlines everything.
   Reduction Reduce(Node* node) final;
 

src/compiler/js-intrinsic-lowering.h

@@ -37,6 +37,8 @@ class V8_EXPORT_PRIVATE JSIntrinsicLowering final
                       DeoptimizationMode mode);
   ~JSIntrinsicLowering() final {}
 
+  const char* reducer_name() const override { return "JSIntrinsicLowering"; }
+
   Reduction Reduce(Node* node) final;
 
  private:

src/compiler/js-native-context-specialization.h

@@ -50,6 +50,10 @@ class JSNativeContextSpecialization final : public AdvancedReducer {
                                 CompilationDependencies* dependencies,
                                 Zone* zone);
 
+  const char* reducer_name() const override {
+    return "JSNativeContextSpecialization";
+  }
+
   Reduction Reduce(Node* node) final;
 
  private:

src/compiler/js-typed-lowering.h

@@ -42,6 +42,8 @@ class V8_EXPORT_PRIVATE JSTypedLowering final
                   Flags flags, JSGraph* jsgraph, Zone* zone);
   ~JSTypedLowering() final {}
 
+  const char* reducer_name() const override { return "JSTypedLowering"; }
+
   Reduction Reduce(Node* node) final;
 
  private:

src/compiler/load-elimination.h

@@ -32,6 +32,8 @@ class V8_EXPORT_PRIVATE LoadElimination final
       : AdvancedReducer(editor), node_states_(zone), jsgraph_(jsgraph) {}
   ~LoadElimination() final {}
 
+  const char* reducer_name() const override { return "LoadElimination"; }
+
   Reduction Reduce(Node* node) final;
 
  private:

src/compiler/machine-operator-reducer.h

@@ -28,6 +28,8 @@ class V8_EXPORT_PRIVATE MachineOperatorReducer final
                                   bool allow_signalling_nan = true);
   ~MachineOperatorReducer();
 
+  const char* reducer_name() const override { return "MachineOperatorReducer"; }
+
   Reduction Reduce(Node* node) override;
 
  private:

src/compiler/pipeline.cc

@@ -485,6 +485,8 @@ class SourcePositionWrapper final : public Reducer {
       : reducer_(reducer), table_(table) {}
   ~SourcePositionWrapper() final {}
 
+  const char* reducer_name() const override { return reducer_->reducer_name(); }
+
   Reduction Reduce(Node* node) final {
     SourcePosition const pos = table_->GetSourcePosition(node);
     SourcePositionTable::Scope position(table_, pos);
@@ -994,6 +996,7 @@ struct UntyperPhase {
   void Run(PipelineData* data, Zone* temp_zone) {
     class RemoveTypeReducer final : public Reducer {
      public:
+      const char* reducer_name() const override { return "RemoveTypeReducer"; }
       Reduction Reduce(Node* node) final {
         if (NodeProperties::IsTyped(node)) {
           NodeProperties::RemoveType(node);

src/compiler/redundancy-elimination.h

@@ -16,6 +16,8 @@ class RedundancyElimination final : public AdvancedReducer {
   RedundancyElimination(Editor* editor, Zone* zone);
   ~RedundancyElimination() final;
 
+  const char* reducer_name() const override { return "RedundancyElimination"; }
+
   Reduction Reduce(Node* node) final;
 
  private:

src/compiler/select-lowering.h

@@ -22,6 +22,8 @@ class SelectLowering final : public Reducer {
   SelectLowering(Graph* graph, CommonOperatorBuilder* common);
   ~SelectLowering();
 
+  const char* reducer_name() const override { return "SelectLowering"; }
+
   Reduction Reduce(Node* node) override;
 
  private:

src/compiler/simplified-operator-reducer.h

@@ -29,6 +29,10 @@ class V8_EXPORT_PRIVATE SimplifiedOperatorReducer final
   SimplifiedOperatorReducer(Editor* editor, JSGraph* jsgraph);
   ~SimplifiedOperatorReducer() final;
 
+  const char* reducer_name() const override {
+    return "SimplifiedOperatorReducer";
+  }
+
   Reduction Reduce(Node* node) final;
 
  private:

src/compiler/tail-call-optimization.h

@@ -24,6 +24,8 @@ class V8_EXPORT_PRIVATE TailCallOptimization final : public Reducer {
   TailCallOptimization(CommonOperatorBuilder* common, Graph* graph)
       : common_(common), graph_(graph) {}
 
+  const char* reducer_name() const override { return "TailCallOptimization"; }
+
   Reduction Reduce(Node* node) final;
 
  private:

src/compiler/typed-optimization.h

@@ -39,6 +39,8 @@ class V8_EXPORT_PRIVATE TypedOptimization final
                     Flags flags, JSGraph* jsgraph);
   ~TypedOptimization();
 
+  const char* reducer_name() const override { return "TypedOptimization"; }
+
   Reduction Reduce(Node* node) final;
 
  private:

src/compiler/typer.cc

@@ -73,6 +73,8 @@ class Typer::Visitor : public Reducer {
         induction_vars_(induction_vars),
         weakened_nodes_(typer->zone()) {}
 
+  const char* reducer_name() const override { return "Typer"; }
+
   Reduction Reduce(Node* node) override {
     if (node->op()->ValueOutputCount() == 0) return NoChange();
     switch (node->opcode()) {

src/compiler/value-numbering-reducer.h

@@ -19,6 +19,8 @@ class V8_EXPORT_PRIVATE ValueNumberingReducer final
   explicit ValueNumberingReducer(Zone* temp_zone, Zone* graph_zone);
   ~ValueNumberingReducer();
 
+  const char* reducer_name() const override { return "ValueNumberingReducer"; }
+
   Reduction Reduce(Node* node) override;
 
  private:

test/unittests/compiler/graph-reducer-unittest.cc

@@ -53,6 +53,7 @@ static TestOperator kOpC1(kOpcodeC1, Operator::kNoWrite, "opc1", 1, 0);
 static TestOperator kOpC2(kOpcodeC2, Operator::kNoWrite, "opc2", 2, 0);
 
 struct MockReducer : public Reducer {
+  MOCK_CONST_METHOD0(reducer_name, const char*());
   MOCK_METHOD1(Reduce, Reduction(Node*));
 };
 
@@ -60,6 +61,7 @@ struct MockReducer : public Reducer {
 // Replaces all "A" operators with "B" operators without creating new nodes.
 class InPlaceABReducer final : public Reducer {
  public:
+  const char* reducer_name() const override { return "InPlaceABReducer"; }
   Reduction Reduce(Node* node) final {
     switch (node->op()->opcode()) {
       case kOpcodeA0:
@@ -85,6 +87,8 @@ class NewABReducer final : public Reducer {
  public:
   explicit NewABReducer(Graph* graph) : graph_(graph) {}
 
+  const char* reducer_name() const override { return "NewABReducer"; }
+
   Reduction Reduce(Node* node) final {
     switch (node->op()->opcode()) {
       case kOpcodeA0:
@@ -111,6 +115,8 @@ class A0Wrapper final : public Reducer {
  public:
   explicit A0Wrapper(Graph* graph) : graph_(graph) {}
 
+  const char* reducer_name() const override { return "A0Wrapper"; }
+
   Reduction Reduce(Node* node) final {
     switch (node->op()->opcode()) {
       case kOpcodeA0:
@@ -130,6 +136,8 @@ class B0Wrapper final : public Reducer {
  public:
   explicit B0Wrapper(Graph* graph) : graph_(graph) {}
 
+  const char* reducer_name() const override { return "B0Wrapper"; }
+
   Reduction Reduce(Node* node) final {
     switch (node->op()->opcode()) {
       case kOpcodeB0:
@@ -147,6 +155,7 @@ class B0Wrapper final : public Reducer {
 // Replaces all "kOpA1" nodes with the first input.
 class A1Forwarder final : public Reducer {
  public:
+  const char* reducer_name() const override { return "A1Forwarder"; }
   Reduction Reduce(Node* node) final {
     switch (node->op()->opcode()) {
       case kOpcodeA1:
@@ -161,6 +170,7 @@ class A1Forwarder final : public Reducer {
 // Replaces all "kOpB1" nodes with the first input.
 class B1Forwarder final : public Reducer {
  public:
+  const char* reducer_name() const override { return "B1Forwarder"; }
   Reduction Reduce(Node* node) final {
     switch (node->op()->opcode()) {
       case kOpcodeB1:
@@ -175,6 +185,7 @@ class B1Forwarder final : public Reducer {
 // Replaces all "B" operators with "C" operators without creating new nodes.
 class InPlaceBCReducer final : public Reducer {
  public:
+  const char* reducer_name() const override { return "InPlaceBCReducer"; }
   Reduction Reduce(Node* node) final {
     switch (node->op()->opcode()) {
       case kOpcodeB0:
@@ -198,6 +209,7 @@ class InPlaceBCReducer final : public Reducer {
 // Swaps the inputs to "kOp2A" and "kOp2B" nodes based on ids.
 class AB2Sorter final : public Reducer {
  public:
+  const char* reducer_name() const override { return "AB2Sorter"; }
   Reduction Reduce(Node* node) final {
     switch (node->op()->opcode()) {
       case kOpcodeA2:
@@ -233,6 +245,7 @@ class AdvancedReducerTest : public TestWithZone {
 TEST_F(AdvancedReducerTest, Replace) {
   struct DummyReducer final : public AdvancedReducer {
     explicit DummyReducer(Editor* editor) : AdvancedReducer(editor) {}
+    const char* reducer_name() const override { return "DummyReducer"; }
     Reduction Reduce(Node* node) final {
       Replace(node, node);
       return NoChange();
@@ -252,6 +265,7 @@ TEST_F(AdvancedReducerTest, Replace) {
 TEST_F(AdvancedReducerTest, Revisit) {
   struct DummyReducer final : public AdvancedReducer {
     explicit DummyReducer(Editor* editor) : AdvancedReducer(editor) {}
+    const char* reducer_name() const override { return "DummyReducer"; }
     Reduction Reduce(Node* node) final {
       Revisit(node);
       return NoChange();
@@ -272,6 +286,9 @@ namespace {
 
 struct ReplaceWithValueReducer final : public AdvancedReducer {
   explicit ReplaceWithValueReducer(Editor* editor) : AdvancedReducer(editor) {}
+  const char* reducer_name() const override {
+    return "ReplaceWithValueReducer";
+  }
   Reduction Reduce(Node* node) final { return NoChange(); }
   using AdvancedReducer::ReplaceWithValue;
 };