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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/common-operator.h"
#include "src/compiler/generic-node-inl.h"
#include "src/compiler/graph-inl.h"
#include "src/compiler/js-context-specialization.h"
#include "src/compiler/js-operator.h"
#include "src/compiler/node-aux-data-inl.h"
#include "src/compiler/node-matchers.h"
#include "src/compiler/node-properties-inl.h"
namespace v8 {
namespace internal {
namespace compiler {
class ContextSpecializationVisitor : public NullNodeVisitor {
public:
explicit ContextSpecializationVisitor(JSContextSpecializer* spec)
: spec_(spec) {}
GenericGraphVisit::Control Post(Node* node) {
switch (node->opcode()) {
case IrOpcode::kJSLoadContext: {
Reduction r = spec_->ReduceJSLoadContext(node);
if (r.Changed() && r.replacement() != node) {
NodeProperties::ReplaceWithValue(node, r.replacement());
node->RemoveAllInputs();
}
break;
}
case IrOpcode::kJSStoreContext: {
Reduction r = spec_->ReduceJSStoreContext(node);
if (r.Changed() && r.replacement() != node) {
NodeProperties::ReplaceWithValue(node, r.replacement());
node->RemoveAllInputs();
}
break;
}
default:
break;
}
return GenericGraphVisit::CONTINUE;
}
private:
JSContextSpecializer* spec_;
};
void JSContextSpecializer::SpecializeToContext() {
NodeProperties::ReplaceWithValue(context_,
jsgraph_->Constant(info_->context()));
ContextSpecializationVisitor visitor(this);
jsgraph_->graph()->VisitNodeInputsFromEnd(&visitor);
}
Reduction JSContextSpecializer::ReduceJSLoadContext(Node* node) {
DCHECK_EQ(IrOpcode::kJSLoadContext, node->opcode());
HeapObjectMatcher<Context> m(NodeProperties::GetValueInput(node, 0));
// If the context is not constant, no reduction can occur.
if (!m.HasValue()) {
return Reducer::NoChange();
}
ContextAccess access = OpParameter<ContextAccess>(node);
// Find the right parent context.
Context* context = *m.Value().handle();
for (int i = access.depth(); i > 0; --i) {
context = context->previous();
}
// 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 Reducer::NoChange();
}
const Operator* op = jsgraph_->javascript()->LoadContext(
0, access.index(), access.immutable());
node->set_op(op);
Handle<Object> context_handle = Handle<Object>(context, info_->isolate());
node->ReplaceInput(0, jsgraph_->Constant(context_handle));
return Reducer::Changed(node);
}
Handle<Object> value =
Handle<Object>(context->get(access.index()), info_->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 Reducer::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.
return Reducer::Replace(jsgraph_->Constant(value));
}
Reduction JSContextSpecializer::ReduceJSStoreContext(Node* node) {
DCHECK_EQ(IrOpcode::kJSStoreContext, node->opcode());
HeapObjectMatcher<Context> m(NodeProperties::GetValueInput(node, 0));
// If the context is not constant, no reduction can occur.
if (!m.HasValue()) {
return Reducer::NoChange();
}
ContextAccess access = OpParameter<ContextAccess>(node);
// The access does not have to look up a parent, nothing to fold.
if (access.depth() == 0) {
return Reducer::NoChange();
}
// Find the right parent context.
Context* context = *m.Value().handle();
for (int i = access.depth(); i > 0; --i) {
context = context->previous();
}
const Operator* op = jsgraph_->javascript()->StoreContext(0, access.index());
node->set_op(op);
Handle<Object> new_context_handle = Handle<Object>(context, info_->isolate());
node->ReplaceInput(0, jsgraph_->Constant(new_context_handle));
return Reducer::Changed(node);
}
} // namespace compiler
} // namespace internal
} // namespace v8
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