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// 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/node-matchers.h"
#include "src/compiler/node-properties.h"
#include "src/contexts.h"
#include "src/objects-inl.h"
namespace v8 {
namespace internal {
namespace compiler {
Reduction JSContextSpecialization::Reduce(Node* node) {
switch (node->opcode()) {
case IrOpcode::kJSLoadContext:
return ReduceJSLoadContext(node);
case IrOpcode::kJSStoreContext:
return ReduceJSStoreContext(node);
default:
break;
}
return NoChange();
}
MaybeHandle<Context> JSContextSpecialization::GetSpecializationContext(
Node* node) {
DCHECK(node->opcode() == IrOpcode::kJSLoadContext ||
node->opcode() == IrOpcode::kJSStoreContext);
Node* const object = NodeProperties::GetValueInput(node, 0);
switch (object->opcode()) {
case IrOpcode::kHeapConstant:
return Handle<Context>::cast(OpParameter<Handle<HeapObject>>(object));
case IrOpcode::kParameter: {
Node* const start = NodeProperties::GetValueInput(object, 0);
DCHECK_EQ(IrOpcode::kStart, start->opcode());
int const index = ParameterIndexOf(object->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.
if (index == start->op()->ValueOutputCount() - 2) {
return context();
}
break;
}
default:
break;
}
return MaybeHandle<Context>();
}
Reduction JSContextSpecialization::ReduceJSLoadContext(Node* node) {
DCHECK_EQ(IrOpcode::kJSLoadContext, node->opcode());
// Get the specialization context from the node.
Handle<Context> context;
if (!GetSpecializationContext(node).ToHandle(&context)) return NoChange();
// Find the right parent context.
const ContextAccess& access = ContextAccessOf(node->op());
for (size_t i = access.depth(); i > 0; --i) {
context = handle(context->previous(), isolate());
}
// If the access itself is mutable, only fold-in the parent.
if (!access.immutable()) {
// The access does not have to look up a parent, nothing to fold.
if (access.depth() == 0) {
return NoChange();
}
const Operator* op = jsgraph_->javascript()->LoadContext(
0, access.index(), access.immutable());
node->ReplaceInput(0, jsgraph_->Constant(context));
NodeProperties::ChangeOp(node, op);
return Changed(node);
}
Handle<Object> value =
handle(context->get(static_cast<int>(access.index())), isolate());
// Even though the context slot is immutable, the context might have escaped
// before the function to which it belongs has initialized the slot.
// 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 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.
if (value->IsConsString()) {
value = String::Flatten(Handle<String>::cast(value), TENURED);
}
Node* constant = jsgraph_->Constant(value);
ReplaceWithValue(node, constant);
return Replace(constant);
}
Reduction JSContextSpecialization::ReduceJSStoreContext(Node* node) {
DCHECK_EQ(IrOpcode::kJSStoreContext, node->opcode());
// Get the specialization context from the node.
Handle<Context> context;
if (!GetSpecializationContext(node).ToHandle(&context)) return NoChange();
// The access does not have to look up a parent, nothing to fold.
const ContextAccess& access = ContextAccessOf(node->op());
if (access.depth() == 0) {
return NoChange();
}
// Find the right parent context.
for (size_t i = access.depth(); i > 0; --i) {
context = handle(context->previous(), isolate());
}
node->ReplaceInput(0, jsgraph_->Constant(context));
NodeProperties::ChangeOp(node, javascript()->StoreContext(0, access.index()));
return Changed(node);
}
Isolate* JSContextSpecialization::isolate() const {
return jsgraph()->isolate();
}
JSOperatorBuilder* JSContextSpecialization::javascript() const {
return jsgraph()->javascript();
}
} // namespace compiler
} // namespace internal
} // namespace v8
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