[compiler][modules] Constant-fold the loads of module cells.

src/compiler/js-context-specialization.h

 // 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.
 
 #ifndef V8_COMPILER_JS_CONTEXT_SPECIALIZATION_H_
 #define V8_COMPILER_JS_CONTEXT_SPECIALIZATION_H_
 
 #include "src/compiler/graph-reducer.h"
 
 namespace v8 {
 namespace internal {
 namespace compiler {
 
 // Forward declarations.
 class JSGraph;
 class JSOperatorBuilder;
 
+// Pair of a context and its distance from some point of reference.
+struct OuterContext {
+  OuterContext() : context(), distance() {}
+  OuterContext(Handle<Context> context_, size_t distance_)
+      : context(context_), distance(distance_) {}
+  Handle<Context> context;
+  size_t distance;
+};
 
 // Specializes a given JSGraph to a given context, potentially constant folding
 // some {LoadContext} nodes or strength reducing some {StoreContext} nodes.
+// Additionally, constant-folds the function parameter if {closure} is given.
+//
+// The context can be the incoming function context or any outer context
+// thereof, as indicated by {outer}'s {distance}.
 class JSContextSpecialization final : public AdvancedReducer {
  public:
   JSContextSpecialization(Editor* editor, JSGraph* jsgraph,
-                          MaybeHandle<Context> context,
+                          Maybe<OuterContext> outer,
                           MaybeHandle<JSFunction> closure)
       : AdvancedReducer(editor),
         jsgraph_(jsgraph),
-        context_(context),
+        outer_(outer),
         closure_(closure) {}
 
   Reduction Reduce(Node* node) final;
 
  private:
   Reduction ReduceParameter(Node* node);
   Reduction ReduceJSLoadContext(Node* node);
   Reduction ReduceJSStoreContext(Node* node);
 
   Reduction SimplifyJSStoreContext(Node* node, Node* new_context,
                                    size_t new_depth);
   Reduction SimplifyJSLoadContext(Node* node, Node* new_context,
                                   size_t new_depth);
 
   Isolate* isolate() const;
   JSOperatorBuilder* javascript() const;
   JSGraph* jsgraph() const { return jsgraph_; }
-  MaybeHandle<Context> context() const { return context_; }
+  Maybe<OuterContext> outer() const { return outer_; }
   MaybeHandle<JSFunction> closure() const { return closure_; }
 
   JSGraph* const jsgraph_;
-  MaybeHandle<Context> context_;
+  Maybe<OuterContext> outer_;
   MaybeHandle<JSFunction> closure_;
 
   DISALLOW_COPY_AND_ASSIGN(JSContextSpecialization);
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_JS_CONTEXT_SPECIALIZATION_H_