[turbofan] Make context specialization into a reducer.

src/compiler/js-context-specialization.cc

Index: src/compiler/js-context-specialization.cc
diff --git a/src/compiler/js-context-specialization.cc b/src/compiler/js-context-specialization.cc
index d11bc6671188e5a6de74ee678fc02f48e46b069b..b2a234be4103966d7ce3eee623f6ed0be4039b53 100644
--- a/src/compiler/js-context-specialization.cc
+++ b/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