[turbofan] Make context specialization into a reducer.

R=bmeurer@chromium.org
BUG=

Review URL: https://codereview.chromium.org/771713002

Cr-Commit-Position: refs/heads/master@{#25600}

src/compiler/js-context-specialization.cc

@@ -6,7 +6,6 @@
 #include "src/compiler/graph-inl.h"
 #include "src/compiler/js-context-specialization.h"
 #include "src/compiler/js-operator.h"
-#include "src/compiler/node-aux-data-inl.h"
 #include "src/compiler/node-matchers.h"
 #include "src/compiler/node-properties-inl.h"
 
@@ -14,45 +13,20 @@ namespace v8 {
 namespace internal {
 namespace compiler {
 
-class ContextSpecializationVisitor : public NullNodeVisitor {
- public:
-  explicit ContextSpecializationVisitor(JSContextSpecializer* spec)
-      : spec_(spec) {}
-
-  void Post(Node* node) {
-    switch (node->opcode()) {
-      case IrOpcode::kJSLoadContext: {
-        Reduction r = spec_->ReduceJSLoadContext(node);
-        if (r.Changed() && r.replacement() != node) {
-          NodeProperties::ReplaceWithValue(node, r.replacement());
-          node->RemoveAllInputs();
-        }
-        break;
-      }
-      case IrOpcode::kJSStoreContext: {
-        Reduction r = spec_->ReduceJSStoreContext(node);
-        if (r.Changed() && r.replacement() != node) {
-          NodeProperties::ReplaceWithValue(node, r.replacement());
-          node->RemoveAllInputs();
-        }
-        break;
-      }
-      default:
-        break;
-    }
-  }
-
- private:
-  JSContextSpecializer* spec_;
-};
-
 
-void JSContextSpecializer::SpecializeToContext() {
-  NodeProperties::ReplaceWithValue(context_,
-                                   jsgraph_->Constant(info_->context()));
-
-  ContextSpecializationVisitor visitor(this);
-  jsgraph_->graph()->VisitNodeInputsFromEnd(&visitor);
+Reduction JSContextSpecializer::Reduce(Node* node) {
+  if (node == context_) {
+    Node* constant = jsgraph_->Constant(info_->context());
+    NodeProperties::ReplaceWithValue(node, constant);
+    return Replace(constant);
+  }
+  if (node->opcode() == IrOpcode::kJSLoadContext) {
+    return ReduceJSLoadContext(node);
+  }
+  if (node->opcode() == IrOpcode::kJSStoreContext) {
+    return ReduceJSStoreContext(node);
+  }
+  return NoChange();
 }
 
 
@@ -62,7 +36,7 @@ Reduction JSContextSpecializer::ReduceJSLoadContext(Node* node) {
   HeapObjectMatcher<Context> m(NodeProperties::GetValueInput(node, 0));
   // If the context is not constant, no reduction can occur.
   if (!m.HasValue()) {
-    return Reducer::NoChange();
+    return NoChange();
   }
 
   const ContextAccess& access = ContextAccessOf(node->op());
@@ -77,14 +51,14 @@ Reduction JSContextSpecializer::ReduceJSLoadContext(Node* node) {
   if (!access.immutable()) {
     // The access does not have to look up a parent, nothing to fold.
     if (access.depth() == 0) {
-      return Reducer::NoChange();
+      return NoChange();
     }
     const Operator* op = jsgraph_->javascript()->LoadContext(
         0, access.index(), access.immutable());
     node->set_op(op);
     Handle<Object> context_handle = Handle<Object>(context, info_->isolate());
     node->ReplaceInput(0, jsgraph_->Constant(context_handle));
-    return Reducer::Changed(node);
+    return Changed(node);
   }
   Handle<Object> value = Handle<Object>(
       context->get(static_cast<int>(access.index())), info_->isolate());
@@ -94,13 +68,15 @@ Reduction JSContextSpecializer::ReduceJSLoadContext(Node* node) {
   // We must be conservative and check if the value in the slot is currently the
   // hole or undefined. If it is neither of these, then it must be initialized.
   if (value->IsUndefined() || value->IsTheHole()) {
-    return Reducer::NoChange();
+    return NoChange();
   }
 
   // Success. The context load can be replaced with the constant.
   // TODO(titzer): record the specialization for sharing code across multiple
   // contexts that have the same value in the corresponding context slot.
-  return Reducer::Replace(jsgraph_->Constant(value));
+  Node* constant = jsgraph_->Constant(value);
+  NodeProperties::ReplaceWithValue(node, constant);
+  return Replace(constant);
 }
 
 
@@ -110,14 +86,14 @@ Reduction JSContextSpecializer::ReduceJSStoreContext(Node* node) {
   HeapObjectMatcher<Context> m(NodeProperties::GetValueInput(node, 0));
   // If the context is not constant, no reduction can occur.
   if (!m.HasValue()) {
-    return Reducer::NoChange();
+    return NoChange();
   }
 
   const ContextAccess& access = ContextAccessOf(node->op());
 
   // The access does not have to look up a parent, nothing to fold.
   if (access.depth() == 0) {
-    return Reducer::NoChange();
+    return NoChange();
   }
 
   // Find the right parent context.
@@ -131,7 +107,7 @@ Reduction JSContextSpecializer::ReduceJSStoreContext(Node* node) {
   Handle<Object> new_context_handle = Handle<Object>(context, info_->isolate());
   node->ReplaceInput(0, jsgraph_->Constant(new_context_handle));
 
-  return Reducer::Changed(node);
+  return Changed(node);
 }
 
 }  // namespace compiler

src/compiler/js-context-specialization.h

@@ -16,12 +16,14 @@ namespace compiler {
 
 // Specializes a given JSGraph to a given context, potentially constant folding
 // some {LoadContext} nodes or strength reducing some {StoreContext} nodes.
-class JSContextSpecializer {
+class JSContextSpecializer : public Reducer {
  public:
   JSContextSpecializer(CompilationInfo* info, JSGraph* jsgraph, Node* context)
       : info_(info), jsgraph_(jsgraph), context_(context) {}
 
-  void SpecializeToContext();
+  virtual Reduction Reduce(Node* node) OVERRIDE;
+
+  // Visible for unit testing.
   Reduction ReduceJSLoadContext(Node* node);
   Reduction ReduceJSStoreContext(Node* node);
 

src/compiler/pipeline.cc

@@ -352,14 +352,16 @@ struct GraphBuilderPhase {
 
 
 struct ContextSpecializerPhase {
-  static const char* phase_name() { return nullptr; }
+  static const char* phase_name() { return "context specializing"; }
 
   void Run(PipelineData* data, Zone* temp_zone) {
     SourcePositionTable::Scope pos(data->source_positions(),
                                    SourcePosition::Unknown());
     JSContextSpecializer spec(data->info(), data->jsgraph(),
                               data->context_node());
-    spec.SpecializeToContext();
+    GraphReducer graph_reducer(data->graph(), temp_zone);
+    graph_reducer.AddReducer(&spec);
+    graph_reducer.ReduceGraph();
   }
 };
 

test/cctest/compiler/test-js-context-specialization.cc

@@ -203,7 +203,7 @@ TEST(SpecializeToContext) {
   JSContextSpecializer spec(t.info(), t.jsgraph(), const_context);
 
   {
-    // Check that SpecializeToContext() replaces values and forwards effects
+    // Check that specialization replaces values and forwards effects
     // correctly, and folds values from constant and non-constant contexts
     Node* effect_in = start;
     Node* load = t.NewNode(t.javascript()->LoadContext(0, slot, true),
@@ -229,8 +229,10 @@ TEST(SpecializeToContext) {
     CheckEffectInput(effect_in, load);
     CheckEffectInput(load, effect_use);
 
-    // Perform the substitution on the entire graph.
-    spec.SpecializeToContext();
+    // Perform the reduction on the entire graph.
+    GraphReducer graph_reducer(t.graph(), t.main_zone());
+    graph_reducer.AddReducer(&spec);
+    graph_reducer.ReduceGraph();
 
     // Effects should have been forwarded (not replaced with a value).
     CheckEffectInput(effect_in, effect_use);