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

src/compiler/js-context-specialization.cc

 // 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.
 
 #include "src/compiler/js-context-specialization.h"
 
 #include "src/compiler/common-operator.h"
 #include "src/compiler/js-graph.h"
 #include "src/compiler/js-operator.h"
 #include "src/compiler/linkage.h"
@@ skipping 65 matching lines @@
     return NoChange();
   }
 
   const Operator* op =
       jsgraph_->javascript()->StoreContext(new_depth, access.index());
   NodeProperties::ReplaceContextInput(node, new_context);
   NodeProperties::ChangeOp(node, op);
   return Changed(node);
 }
 
+namespace {
+
+bool IsContextParameter(Node* node) {
+  DCHECK_EQ(IrOpcode::kParameter, node->opcode());
+  Node* const start = NodeProperties::GetValueInput(node, 0);
+  DCHECK_EQ(IrOpcode::kStart, start->opcode());
+  int const index = ParameterIndexOf(node->op());
+  // The context is always the last parameter to a JavaScript function, and
+  // {Parameter} indices start at -1, so value outputs of {Start} look like
+  // this: closure, receiver, param0, ..., paramN, context.
+  return index == start->op()->ValueOutputCount() - 2;
+}
+
+MaybeHandle<Context> GetSpecializationContext(Node* node,

[Michael Starzinger, 2017/05/03 17:28:16]

nit: Needs a short comment explaining the semantics of "requested_depth" IMHO.

[neis, 2017/05/04 10:36:21]

Done.

+                                              size_t* requested_depth,
+                                              Maybe<OuterContext> maybe_outer) {
+  switch (node->opcode()) {
+    case IrOpcode::kHeapConstant:
+      return Handle<Context>::cast(OpParameter<Handle<HeapObject>>(node));
+    case IrOpcode::kParameter: {
+      OuterContext outer;
+      if (maybe_outer.To(&outer) && IsContextParameter(node) &&
+          *requested_depth >= outer.distance) {
+        *requested_depth -= outer.distance;
+        return outer.context;
+      }
+      break;
+    }
+    default:
+      break;
+  }
+  return MaybeHandle<Context>();
+}
+
+}  // anonymous namespace
+
 Reduction JSContextSpecialization::ReduceJSLoadContext(Node* node) {
   DCHECK_EQ(IrOpcode::kJSLoadContext, node->opcode());
 
   const ContextAccess& access = ContextAccessOf(node->op());
   size_t depth = access.depth();
 
   // First walk up the context chain in the graph as far as possible.
-  Node* outer = NodeProperties::GetOuterContext(node, &depth);
+  Node* context = NodeProperties::GetOuterContext(node, &depth);
 
   Handle<Context> concrete;
-  if (!NodeProperties::GetSpecializationContext(outer, context())
-           .ToHandle(&concrete)) {
+  if (!GetSpecializationContext(context, &depth, outer()).ToHandle(&concrete)) {
     // We do not have a concrete context object, so we can only partially reduce
     // the load by folding-in the outer context node.
-    return SimplifyJSLoadContext(node, outer, depth);
+    return SimplifyJSLoadContext(node, context, depth);
   }
 
   // Now walk up the concrete context chain for the remaining depth.
   for (; depth > 0; --depth) {
     concrete = handle(concrete->previous(), isolate());
   }
 
   if (!access.immutable()) {
     // We found the requested context object but since the context slot is
     // mutable we can only partially reduce the load.
@@ skipping 21 matching lines @@
 
 
 Reduction JSContextSpecialization::ReduceJSStoreContext(Node* node) {
   DCHECK_EQ(IrOpcode::kJSStoreContext, node->opcode());
 
   const ContextAccess& access = ContextAccessOf(node->op());
   size_t depth = access.depth();
 
   // First walk up the context chain in the graph until we reduce the depth to 0
   // or hit a node that does not have a CreateXYZContext operator.
-  Node* outer = NodeProperties::GetOuterContext(node, &depth);
+  Node* context = NodeProperties::GetOuterContext(node, &depth);
 
   Handle<Context> concrete;
-  if (!NodeProperties::GetSpecializationContext(outer, context())
-           .ToHandle(&concrete)) {
+  if (!GetSpecializationContext(context, &depth, outer()).ToHandle(&concrete)) {
     // We do not have a concrete context object, so we can only partially reduce
     // the load by folding-in the outer context node.
-    return SimplifyJSStoreContext(node, outer, depth);
+    return SimplifyJSStoreContext(node, context, depth);
   }
 
   // Now walk up the concrete context chain for the remaining depth.
   for (; depth > 0; --depth) {
     concrete = handle(concrete->previous(), isolate());
   }
 
   return SimplifyJSStoreContext(node, jsgraph()->Constant(concrete), depth);
 }
 
 
 Isolate* JSContextSpecialization::isolate() const {
   return jsgraph()->isolate();
 }
 
 
 JSOperatorBuilder* JSContextSpecialization::javascript() const {
   return jsgraph()->javascript();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8