[turbofan] Move context specialization into JSContextSpecializer.

src/compiler/ast-graph-builder.cc

Index: src/compiler/ast-graph-builder.cc
diff --git a/src/compiler/ast-graph-builder.cc b/src/compiler/ast-graph-builder.cc
index 0abc9918df6595454e83f095732f71049ddc4088..c0f706d3b178e7fc17b185ce5c5d60251bacb7e4 100644
--- a/src/compiler/ast-graph-builder.cc
+++ b/src/compiler/ast-graph-builder.cc
@@ -483,31 +483,18 @@ Node* AstGraphBuilder::GetFunctionClosure() {
 }
 
 
-void AstGraphBuilder::CreateFunctionContext(bool constant_context) {
-  function_context_.set(constant_context
-                            ? jsgraph()->HeapConstant(info()->context())
-                            : NewOuterContextParam());
-}
-
-
-Node* AstGraphBuilder::NewOuterContextParam() {
-  // Parameter (arity + 1) is special for the outer context of the function
-  const Operator* op =
-      common()->Parameter(info()->num_parameters_including_this(), "%context");
-  return NewNode(op, graph()->start());
-}
-
-
-Node* AstGraphBuilder::NewCurrentContextOsrValue() {
-  // TODO(titzer): use a real OSR value here; a parameter works by accident.
-  // Parameter (arity + 1) is special for the outer context of the function
-  const Operator* op = common()->Parameter(
-      info()->num_parameters_including_this(), "%osr-context");
-  return NewNode(op, graph()->start());
+Node* AstGraphBuilder::GetFunctionContext() {
+  if (!function_context_.is_set()) {
+    const Operator* op = common()->Parameter(
+        info()->num_parameters_including_this(), "%context");
+    Node* node = NewNode(op, graph()->start());
+    function_context_.set(node);
+  }
+  return function_context_.get();
 }
 
 
-bool AstGraphBuilder::CreateGraph(bool constant_context, bool stack_check) {
+bool AstGraphBuilder::CreateGraph(bool stack_check) {
   Scope* scope = info()->scope();
   DCHECK(graph() != NULL);
 
@@ -526,8 +513,7 @@ bool AstGraphBuilder::CreateGraph(bool constant_context, bool stack_check) {
   }
 
   // Initialize the incoming context.
-  CreateFunctionContext(constant_context);
-  ContextScope incoming(this, scope, function_context_.get());
+  ContextScope incoming(this, scope, GetFunctionContext());
 
   // Initialize control scope.
   ControlScope control(this);
@@ -547,7 +533,7 @@ bool AstGraphBuilder::CreateGraph(bool constant_context, bool stack_check) {
   if (info()->num_heap_slots() > 0) {
     // Push a new inner context scope for the function.
     Node* inner_context =
-        BuildLocalFunctionContext(function_context_.get(), patched_receiver);
+        BuildLocalFunctionContext(GetFunctionContext(), patched_receiver);
     ContextScope top_context(this, scope, inner_context);
     CreateGraphBody(stack_check);
   } else {
@@ -3636,7 +3622,7 @@ Node* AstGraphBuilder::BuildLoadBuiltinsObject() {
 Node* AstGraphBuilder::BuildLoadGlobalObject() {
   const Operator* load_op =
       javascript()->LoadContext(0, Context::GLOBAL_OBJECT_INDEX, true);
-  return NewNode(load_op, function_context_.get());
+  return NewNode(load_op, GetFunctionContext());
 }
 
 
@@ -4063,7 +4049,9 @@ void AstGraphBuilder::Environment::PrepareForLoop(BitVector* assigned,
     // Introduce phis for all context values in the case of an OSR graph.
     for (int i = 0; i < static_cast<int>(contexts()->size()); ++i) {
       Node* val = contexts()->at(i);
-      if (!IrOpcode::IsConstantOpcode(val->opcode())) {
+      if (!IrOpcode::IsConstantOpcode(val->opcode()) &&
+          (val != builder_->GetFunctionContext() ||
+           !builder_->info()->is_context_specializing())) {
         contexts()->at(i) = builder_->NewPhi(1, val, control);
       }
     }
@@ -4090,14 +4078,21 @@ void AstGraphBuilder::Environment::PrepareForLoop(BitVector* assigned,
     // Rename all the contexts in the environment.
     // The innermost context is the OSR value, and the outer contexts are
     // reconstructed by dynamically walking up the context chain.
+    // TODO(titzer): use a real OSR value here; a parameter works by accident.

[titzer, 2015/07/03 09:28:17]

To get rid of this TODO, we need a special OSR value that will represent the
context on the stack that the linkage knows about. Then context specialization
won't be confused by seeing a weird parameter that really represents an OSR
value.

We should do this in a separate CL first.

[Michael Starzinger, 2015/07/06 13:08:40]

Done, see: https://codereview.chromium.org/1213043005/

+    Node* innermost_context = graph->NewNode(
+        builder_->common()->Parameter(
+            builder_->info()->num_parameters_including_this(), "%osr-context"),
+        graph->start());
     Node* osr_context = nullptr;
     const Operator* op =
         builder_->javascript()->LoadContext(0, Context::PREVIOUS_INDEX, true);
     int last = static_cast<int>(contexts()->size() - 1);
     for (int i = last; i >= 0; i--) {
       Node* val = contexts()->at(i);
-      if (!IrOpcode::IsConstantOpcode(val->opcode())) {
-        osr_context = (i == last) ? builder_->NewCurrentContextOsrValue()
+      if (!IrOpcode::IsConstantOpcode(val->opcode()) &&
+          (val != builder_->GetFunctionContext() ||
+           !builder_->info()->is_context_specializing())) {
+        osr_context = (i == last) ? innermost_context
                                   : graph->NewNode(op, osr_context, osr_context,
                                                    osr_loop_entry);
         contexts()->at(i) = builder_->MergeValue(val, osr_context, control);