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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();
}
Reduction JSContextSpecialization::SimplifyJSLoadContext(Node* node,
Node* new_context,
size_t new_depth) {
DCHECK_EQ(IrOpcode::kJSLoadContext, node->opcode());
const ContextAccess& access = ContextAccessOf(node->op());
DCHECK_LE(new_depth, access.depth());
if (new_depth == access.depth() &&
new_context == NodeProperties::GetContextInput(node)) {
return NoChange();
}
const Operator* op = jsgraph_->javascript()->LoadContext(
new_depth, access.index(), access.immutable());
NodeProperties::ReplaceContextInput(node, new_context);
NodeProperties::ChangeOp(node, op);
return Changed(node);
}
Reduction JSContextSpecialization::SimplifyJSStoreContext(Node* node,
Node* new_context,
size_t new_depth) {
DCHECK_EQ(IrOpcode::kJSStoreContext, node->opcode());
const ContextAccess& access = ContextAccessOf(node->op());
DCHECK_LE(new_depth, access.depth());
if (new_depth == access.depth() &&
new_context == NodeProperties::GetContextInput(node)) {
return NoChange();
}
const Operator* op =
jsgraph_->javascript()->StoreContext(new_depth, access.index());
NodeProperties::ReplaceContextInput(node, new_context);
NodeProperties::ChangeOp(node, op);
return Changed(node);
}
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);
Handle<Context> concrete;
if (!NodeProperties::GetSpecializationContext(outer, context())
.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);
}
// 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.
return SimplifyJSLoadContext(node, jsgraph()->Constant(concrete), depth);
}
// 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. Only if it is neither of these, can we be sure that
// it won't change anymore.
Handle<Object> value(concrete->get(static_cast<int>(access.index())),
isolate());
if (value->IsUndefined(isolate()) || value->IsTheHole(isolate())) {
return SimplifyJSLoadContext(node, jsgraph()->Constant(concrete), depth);
}
// 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.
Node* constant = jsgraph_->Constant(value);
ReplaceWithValue(node, constant);
return Replace(constant);
}
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);
Handle<Context> concrete;
if (!NodeProperties::GetSpecializationContext(outer, context())
.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);
}
// 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
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