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Unified Diff: src/compiler/js-context-specialization.cc

Issue 426233002: Land the Fan (disabled) (Closed) Base URL: https://v8.googlecode.com/svn/branches/bleeding_edge
Patch Set: Review feedback, rebase and "git cl format" Created 6 years, 5 months ago
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Index: src/compiler/js-context-specialization.cc
diff --git a/src/compiler/js-context-specialization.cc b/src/compiler/js-context-specialization.cc
new file mode 100644
index 0000000000000000000000000000000000000000..658c99bc4dd81b6fa20d458b2904c939218d97e0
--- /dev/null
+++ b/src/compiler/js-context-specialization.cc
@@ -0,0 +1,93 @@
+// 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/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 {
+
+// TODO(titzer): factor this out to a common routine with js-typed-lowering.
+static void ReplaceEffectfulWithValue(Node* node, Node* value) {
+ Node* effect = NodeProperties::GetEffectInput(node);
+
+ // Requires distinguishing between value and effect edges.
+ UseIter iter = node->uses().begin();
+ while (iter != node->uses().end()) {
+ if (NodeProperties::IsEffectEdge(iter.edge())) {
+ iter = iter.UpdateToAndIncrement(effect);
+ } else {
+ iter = iter.UpdateToAndIncrement(value);
+ }
+ }
+}
+
+
+void JSContextSpecializer::SpecializeToContext() {
+ ValueMatcher<Handle<Context> > match(context_);
+
+ // Iterate over all uses of the context and try to replace {LoadContext}
+ // nodes with their values from the constant context.
+ UseIter iter = match.node()->uses().begin();
+ while (iter != match.node()->uses().end()) {
+ Node* use = *iter;
+ if (use->opcode() == IrOpcode::kJSLoadContext) {
+ Reduction r = ReduceJSLoadContext(use);
+ if (r.Changed() && r.replacement() != use) {
+ ReplaceEffectfulWithValue(use, r.replacement());
+ }
+ }
+ ++iter;
+ }
+}
+
+
+Reduction JSContextSpecializer::ReduceJSLoadContext(Node* node) {
+ ASSERT_EQ(IrOpcode::kJSLoadContext, node->opcode());
+
+ ContextAccess access =
+ static_cast<Operator1<ContextAccess>*>(node->op())->parameter();
+
+ // Find the right parent context.
+ Context* context = *info_->context();
+ 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();
+ }
+ 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));
+}
+}
+}
+} // namespace v8::internal::compiler
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