[turbofan] Reduce context accesses during typed lowering.

src/compiler/access-builder.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/access-builder.h"
 #include "src/types-inl.h"
 
 namespace v8 {
 namespace internal {
 namespace compiler {
@@ skipping 55 matching lines @@
 
 
 // static
 FieldAccess AccessBuilder::ForValue() {
   return {kTaggedBase, JSValue::kValueOffset, Handle<Name>(), Type::Any(),
           kMachAnyTagged};
 }
 
 
 // static
+FieldAccess AccessBuilder::ForContextSlot(size_t index) {
+  int offset = Context::kHeaderSize + static_cast<int>(index) * kPointerSize;
+  DCHECK_EQ(offset,
+            Context::SlotOffset(static_cast<int>(index)) + kHeapObjectTag);
+  return {kTaggedBase, offset, Handle<Name>(), Type::Any(), kMachAnyTagged};
+}
+
+
+// static
 ElementAccess AccessBuilder::ForFixedArrayElement() {
   return {kTaggedBase, FixedArray::kHeaderSize, Type::Any(), kMachAnyTagged};
 }
 
 
 // static
 ElementAccess AccessBuilder::ForTypedArrayElement(ExternalArrayType type,
                                                   bool is_external) {
   BaseTaggedness taggedness = is_external ? kUntaggedBase : kTaggedBase;
   int header_size = is_external ? 0 : FixedTypedArrayBase::kDataOffset;
@@ skipping 16 matching lines @@
     case kExternalFloat64Array:
       return {taggedness, header_size, Type::Number(), kMachFloat64};
   }
   UNREACHABLE();
   return {kUntaggedBase, 0, Type::None(), kMachNone};
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8