[turbofan] Rename context stack as part of the environment for OSR.

src/compiler/ast-graph-builder.cc

 // 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/ast-graph-builder.h"
 
 #include "src/compiler.h"
 #include "src/compiler/ast-loop-assignment-analyzer.h"
 #include "src/compiler/control-builders.h"
 #include "src/compiler/linkage.h"
@@ skipping 91 matching lines @@
 
 // Scoped class tracking context objects created by the visitor. Represents
 // mutations of the context chain within the function body and allows to
 // change the current {scope} and {context} during visitation.
 class AstGraphBuilder::ContextScope BASE_EMBEDDED {
  public:
   ContextScope(AstGraphBuilder* builder, Scope* scope, Node* context)
       : builder_(builder),
         outer_(builder->execution_context()),
         scope_(scope),
-        context_(context) {
-    builder_->set_execution_context(this);  // Push.
+        depth_(builder_->environment()->ContextStackDepth()) {
+    builder_->environment()->PushContext(context);  // Push.
+    builder_->set_execution_context(this);
   }
 
   ~ContextScope() {
     builder_->set_execution_context(outer_);  // Pop.
+    builder_->environment()->PopContext();
+    CHECK_EQ(depth_, builder_->environment()->ContextStackDepth());
   }
 
   // Current scope during visitation.
   Scope* scope() const { return scope_; }
-  // Current context node during visitation.
-  Node* context() const { return context_; }
 
  private:
   AstGraphBuilder* builder_;
   ContextScope* outer_;
   Scope* scope_;
-  Node* context_;
+  int depth_;
 };
 
 
 // Scoped class tracking control statements entered by the visitor. There are
 // different types of statements participating in this stack to properly track
 // local as well as non-local control flow:
 //  - IterationStatement : Allows proper 'break' and 'continue' behavior.
 //  - BreakableStatement : Allows 'break' from block and switch statements.
 //  - TryCatchStatement  : Intercepts 'throw' and implicit exceptional edges.
 //  - TryFinallyStatement: Intercepts 'break', 'continue', 'throw' and 'return'.
@@ skipping 231 matching lines @@
 AstGraphBuilder::AstGraphBuilder(Zone* local_zone, CompilationInfo* info,
                                  JSGraph* jsgraph, LoopAssignmentAnalysis* loop)
     : local_zone_(local_zone),
       info_(info),
       jsgraph_(jsgraph),
       environment_(nullptr),
       ast_context_(nullptr),
       globals_(0, local_zone),
       execution_control_(nullptr),
       execution_context_(nullptr),
+      function_context_(nullptr),
       input_buffer_size_(0),
       input_buffer_(nullptr),
       exit_control_(nullptr),
       loop_assignment_analysis_(loop) {
   InitializeAstVisitor(info->isolate(), local_zone);
 }
 
 
 Node* AstGraphBuilder::GetFunctionClosure() {
   if (!function_closure_.is_set()) {
     const Operator* op =
         common()->Parameter(Linkage::kJSFunctionCallClosureParamIndex);
     Node* node = NewNode(op, graph()->start());
     function_closure_.set(node);
   }
   return function_closure_.get();
 }
 
 
 Node* AstGraphBuilder::GetFunctionContext() {
-  if (!function_context_.is_set()) {
-    // Parameter (arity + 1) is special for the outer context of the function
-    const Operator* op = common()->Parameter(info()->num_parameters() + 1);
-    Node* node = NewNode(op, graph()->start());
-    function_context_.set(node);
-  }
-  return function_context_.get();
+  DCHECK(function_context_ != nullptr);
+  return function_context_;
 }
 
 
+Node* AstGraphBuilder::NewOuterContextParam() {
+  // Parameter (arity + 1) is special for the outer context of the function
+  const Operator* op = common()->Parameter(info()->num_parameters() + 1);
+  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() + 1);
+  return NewNode(op, graph()->start());
+}
+
+
 bool AstGraphBuilder::CreateGraph() {
   Scope* scope = info()->scope();
   DCHECK(graph() != NULL);
 
   // Set up the basic structure of the graph.
   int parameter_count = info()->num_parameters();
   graph()->SetStart(graph()->NewNode(common()->Start(parameter_count)));
 
   // Initialize control scope.
   ControlScope control(this, 0);
 
   // Initialize the top-level environment.
   Environment env(this, scope, graph()->start());
   set_environment(&env);
 
   if (info()->is_osr()) {
     // Use OSR normal entry as the start of the top-level environment.
     // It will be replaced with {Dead} after typing and optimizations.
     NewNode(common()->OsrNormalEntry());
   }
 
   // Initialize the incoming context.
-  Node* incoming_context = GetFunctionContext();
-  ContextScope incoming(this, scope, incoming_context);
+  function_context_ = NewOuterContextParam();
+  ContextScope incoming(this, scope, function_context_);
 
   // Build receiver check for sloppy mode if necessary.
   // TODO(mstarzinger/verwaest): Should this be moved back into the CallIC?
   Node* original_receiver = env.Lookup(scope->receiver());
   Node* patched_receiver = BuildPatchReceiverToGlobalProxy(original_receiver);
   env.Bind(scope->receiver(), patched_receiver);
 
-  // Build node to initialize local function context.
   Node* closure = GetFunctionClosure();

[Michael Starzinger, 2015/02/17 10:34:37]

nit: The closure is only needed in the case we build a function-context, can we
move it into the branch?

[titzer, 2015/02/17 10:44:16]

Tried that, but nope. GetFunctionClosure() has a side effect. Rename?

-  Node* inner_context = BuildLocalFunctionContext(incoming_context, closure);
+  bool ok;
+  int heap_slots = info()->num_heap_slots() - Context::MIN_CONTEXT_SLOTS;
+  if (heap_slots > 0) {
+    // Push a new inner context scope for the function.
+    Node* inner_context = BuildLocalFunctionContext(function_context_, closure);
+    ContextScope top_context(this, scope, inner_context);
+    ok = CreateGraphBody();
+  } else {
+    // Simply use the outer function context in building the graph.
+    ok = CreateGraphBody();
+  }
 
-  // Push top-level function context for the function body.
-  ContextScope top_context(this, scope, inner_context);
+  // Finish the basic structure of the graph.
+  if (ok) {

[Michael Starzinger, 2015/02/17 10:34:37]

It should be safe to also do this in the case of stack-overflow, because
environments are still intact. Let's try to avoid this "ok" dance here and just
always add the end.

[titzer, 2015/02/17 10:44:16]

Tried that too, but nope, the environment's control dependency may be NULL in
some cases => crash.

[titzer, 2015/02/17 11:24:36]

Disregard previous comment.

+    environment()->UpdateControlDependency(exit_control());
+    graph()->SetEnd(NewNode(common()->End()));
+  }
 
+  return ok;
+}
+
+
+bool AstGraphBuilder::CreateGraphBody() {
+  Scope* scope = info()->scope();
   // Build the arguments object if it is used.
   BuildArgumentsObject(scope->arguments());
 
   // Build rest arguments array if it is used.
   int rest_index;
   Variable* rest_parameter = scope->rest_parameter(&rest_index);
   BuildRestArgumentsArray(rest_parameter, rest_index);
 
   // Emit tracing call if requested to do so.
   if (FLAG_trace) {
@@ skipping 19 matching lines @@
   // Emit tracing call if requested to do so.
   if (FLAG_trace) {
     // TODO(mstarzinger): Only traces implicit return.
     Node* return_value = jsgraph()->UndefinedConstant();
     NewNode(javascript()->CallRuntime(Runtime::kTraceExit, 1), return_value);
   }
 
   // Return 'undefined' in case we can fall off the end.
   BuildReturn(jsgraph()->UndefinedConstant());
 
-  // Finish the basic structure of the graph.
-  environment()->UpdateControlDependency(exit_control());
-  graph()->SetEnd(NewNode(common()->End()));
-
   return true;
 }
 
 
 // Left-hand side can only be a property, a global or a variable slot.
 enum LhsKind { VARIABLE, NAMED_PROPERTY, KEYED_PROPERTY };
 
 
 // Determine the left-hand side kind of an assignment.
 static LhsKind DetermineLhsKind(Expression* expr) {
   Property* property = expr->AsProperty();
   DCHECK(expr->IsValidReferenceExpression());
   LhsKind lhs_kind =
       (property == NULL) ? VARIABLE : (property->key()->IsPropertyName())
                                           ? NAMED_PROPERTY
                                           : KEYED_PROPERTY;
   return lhs_kind;
 }
 
 
 AstGraphBuilder::Environment::Environment(AstGraphBuilder* builder,
                                           Scope* scope,
                                           Node* control_dependency)
     : builder_(builder),
       parameters_count_(scope->num_parameters() + 1),
       locals_count_(scope->num_stack_slots()),
       values_(builder_->local_zone()),
+      contexts_(builder_->local_zone()),
       control_dependency_(control_dependency),
       effect_dependency_(control_dependency),
       parameters_node_(nullptr),
       locals_node_(nullptr),
       stack_node_(nullptr) {
   DCHECK_EQ(scope->num_parameters() + 1, parameters_count());
 
   // Bind the receiver variable.
   Node* receiver = builder->graph()->NewNode(common()->Parameter(0),
                                              builder->graph()->start());
@@ skipping 12 matching lines @@
   values()->insert(values()->end(), locals_count(), undefined_constant);
 }
 
 
 AstGraphBuilder::Environment::Environment(
     const AstGraphBuilder::Environment* copy)
     : builder_(copy->builder_),
       parameters_count_(copy->parameters_count_),
       locals_count_(copy->locals_count_),
       values_(copy->zone()),
+      contexts_(copy->zone()),
       control_dependency_(copy->control_dependency_),
       effect_dependency_(copy->effect_dependency_),
       parameters_node_(copy->parameters_node_),
       locals_node_(copy->locals_node_),
       stack_node_(copy->stack_node_) {
   const size_t kStackEstimate = 7;  // optimum from experimentation!
   values_.reserve(copy->values_.size() + kStackEstimate);
   values_.insert(values_.begin(), copy->values_.begin(), copy->values_.end());
+  contexts_.reserve(copy->contexts_.size());
+  contexts_.insert(contexts_.begin(), copy->contexts_.begin(),
+                   copy->contexts_.end());
 }
 
 
 void AstGraphBuilder::Environment::UpdateStateValues(Node** state_values,
                                                      int offset, int count) {
   bool should_update = false;
   Node** env_values = (count == 0) ? NULL : &values()->at(offset);
   if (*state_values == NULL || (*state_values)->InputCount() != count) {
     should_update = true;
   } else {
@@ skipping 84 matching lines @@
   return environment()->Pop();
 }
 
 
 Scope* AstGraphBuilder::current_scope() const {
   return execution_context_->scope();
 }
 
 
 Node* AstGraphBuilder::current_context() const {
-  return execution_context_->context();
+  return environment()->Context();
 }
 
 
 void AstGraphBuilder::ControlScope::PerformCommand(Command command,
                                                    Statement* target,
                                                    Node* value) {
   Environment* env = environment()->CopyAsUnreachable();
   ControlScope* current = this;
   while (current != NULL) {
     if (current->Execute(command, target, value)) break;
@@ skipping 522 matching lines @@
     Visit(stmt->try_block());
   }
   try_control.EndTry();
 
   // Create a catch scope that binds the exception.
   Node* exception = try_control.GetExceptionNode();
   Unique<String> name = MakeUnique(stmt->variable()->name());
   const Operator* op = javascript()->CreateCatchContext(name);
   Node* context = NewNode(op, exception, GetFunctionClosure());
   PrepareFrameState(context, BailoutId::None());
-  ContextScope scope(this, stmt->scope(), context);
-  DCHECK(stmt->scope()->declarations()->is_empty());
-
-  // Evaluate the catch-block.
-  Visit(stmt->catch_block());
+  {
+    ContextScope scope(this, stmt->scope(), context);
+    DCHECK(stmt->scope()->declarations()->is_empty());
+    // Evaluate the catch-block.
+    Visit(stmt->catch_block());
+  }
   try_control.EndCatch();
 
   // TODO(mstarzinger): Remove bailout once everything works.
   if (!FLAG_turbo_exceptions) SetStackOverflow();
 }
 
 
 void AstGraphBuilder::VisitTryFinallyStatement(TryFinallyStatement* stmt) {
   TryFinallyBuilder try_control(this);
 
@@ skipping 1202 matching lines @@
   receiver_check.Then();
   environment()->Push(BuildLoadGlobalProxy());
   receiver_check.Else();
   environment()->Push(receiver);
   receiver_check.End();
   return environment()->Pop();
 }
 
 
 Node* AstGraphBuilder::BuildLocalFunctionContext(Node* context, Node* closure) {
-  int heap_slots = info()->num_heap_slots() - Context::MIN_CONTEXT_SLOTS;
-  if (heap_slots <= 0) return context;
-
   // Allocate a new local context.
   const Operator* op = javascript()->CreateFunctionContext();
   Node* local_context = NewNode(op, closure);
 
   // Copy parameters into context if necessary.
   int num_parameters = info()->scope()->num_parameters();
   for (int i = 0; i < num_parameters; i++) {
     Variable* variable = info()->scope()->parameter(i);
     if (!variable->IsContextSlot()) continue;
     // Temporary parameter node. The parameter indices are shifted by 1
@@ skipping 553 matching lines @@
   if (exit_control() != NULL) {
     exit = MergeControl(exit_control(), exit);
   }
   environment()->MarkAsUnreachable();
   set_exit_control(exit);
 }
 
 
 void AstGraphBuilder::Environment::Merge(Environment* other) {
   DCHECK(values_.size() == other->values_.size());
+  DCHECK(contexts_.size() <= other->contexts_.size());
 
   // Nothing to do if the other environment is dead.
   if (other->IsMarkedAsUnreachable()) return;
 
   // Resurrect a dead environment by copying the contents of the other one and
   // placing a singleton merge as the new control dependency.
   if (this->IsMarkedAsUnreachable()) {
     Node* other_control = other->control_dependency_;
     Node* inputs[] = {other_control};
     control_dependency_ =
@@ skipping 13 matching lines @@
   // the current environment's effect dependency accordingly.
   Node* effect = builder_->MergeEffect(this->GetEffectDependency(),
                                        other->GetEffectDependency(), control);
   UpdateEffectDependency(effect);
 
   // Introduce Phi nodes for values that have differing input at merge points,
   // potentially extending an existing Phi node if possible.
   for (int i = 0; i < static_cast<int>(values_.size()); ++i) {
     values_[i] = builder_->MergeValue(values_[i], other->values_[i], control);
   }
+  for (int i = 0; i < static_cast<int>(contexts_.size()); ++i) {
+    contexts_[i] =
+        builder_->MergeValue(contexts_[i], other->contexts_[i], control);
+  }
 }
 
 
 void AstGraphBuilder::Environment::PrepareForLoop(BitVector* assigned,
                                                   bool is_osr) {
   int size = static_cast<int>(values()->size());
 
   Node* control = builder_->NewLoop();
   if (assigned == nullptr) {
     // Assume that everything is updated in the loop.
     for (int i = 0; i < size; ++i) {
-      Node* phi = builder_->NewPhi(1, values()->at(i), control);
-      values()->at(i) = phi;
+      values()->at(i) = builder_->NewPhi(1, values()->at(i), control);
     }
   } else {
     // Only build phis for those locals assigned in this loop.
     for (int i = 0; i < size; ++i) {
       if (i < assigned->length() && !assigned->Contains(i)) continue;
       Node* phi = builder_->NewPhi(1, values()->at(i), control);
       values()->at(i) = phi;
     }
   }
   Node* effect = builder_->NewEffectPhi(1, GetEffectDependency(), control);
   UpdateEffectDependency(effect);
 
+  if (builder_->info()->is_osr()) {
+    // 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())) {
+        contexts()->at(i) = builder_->NewPhi(1, val, control);
+      }
+    }
+  }
+
   if (is_osr) {
     // Merge OSR values as inputs to the phis of the loop.
     Graph* graph = builder_->graph();
     Node* osr_loop_entry = builder_->graph()->NewNode(
         builder_->common()->OsrLoopEntry(), graph->start(), graph->start());
 
     builder_->MergeControl(control, osr_loop_entry);
     builder_->MergeEffect(effect, osr_loop_entry, control);
 
     for (int i = 0; i < size; ++i) {
       Node* val = values()->at(i);
       if (!IrOpcode::IsConstantOpcode(val->opcode())) {
         Node* osr_value =
             graph->NewNode(builder_->common()->OsrValue(i), osr_loop_entry);
         values()->at(i) = builder_->MergeValue(val, osr_value, control);
       }
     }
+
+    // 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.
+    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()
+                                  : graph->NewNode(op, osr_context, osr_context,
+                                                   osr_loop_entry);
+        contexts()->at(i) = builder_->MergeValue(val, osr_context, control);
+      } else {
+        osr_context = val;
+      }
+    }
   }
 }
 
 
 Node* AstGraphBuilder::NewPhi(int count, Node* input, Node* control) {
   const Operator* phi_op = common()->Phi(kMachAnyTagged, count);
   Node** buffer = EnsureInputBufferSize(count + 1);
   MemsetPointer(buffer, input, count);
   buffer[count] = control;
   return graph()->NewNode(phi_op, count + 1, buffer, true);
@@ skipping 69 matching lines @@
     Node* dead_node = graph()->NewNode(common()->Dead());
     dead_control_.set(dead_node);
     return dead_node;
   }
   return dead_control_.get();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8