Simplify computation of environment stack delta.

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 121 matching lines @@
 
 // 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'.
 class AstGraphBuilder::ControlScope BASE_EMBEDDED {
  public:
-  ControlScope(AstGraphBuilder* builder, int stack_delta)
+  explicit ControlScope(AstGraphBuilder* builder)
       : builder_(builder),
         outer_(builder->execution_control()),
-        stack_delta_(stack_delta) {
+        stack_height_(builder->environment()->stack_height()) {
     builder_->set_execution_control(this);  // Push.
   }
 
   virtual ~ControlScope() {
     builder_->set_execution_control(outer_);  // Pop.
   }
 
   // Either 'break' or 'continue' to the target statement.
   void BreakTo(BreakableStatement* target);
   void ContinueTo(BreakableStatement* target);
@@ skipping 26 matching lines @@
         return true;
       case CMD_BREAK:
       case CMD_CONTINUE:
         break;
     }
     return false;
   }
 
   Environment* environment() { return builder_->environment(); }
   AstGraphBuilder* builder() const { return builder_; }
-  int stack_delta() const { return stack_delta_; }
+  int stack_height() const { return stack_height_; }
 
  private:
   AstGraphBuilder* builder_;
   ControlScope* outer_;
-  int stack_delta_;
+  int stack_height_;
 };
 
 
 // Helper class for a try-finally control scope. It can record intercepted
 // control-flow commands that cause entry into a finally-block, and re-apply
 // them after again leaving that block. Special tokens are used to identify
 // paths going through the finally-block to dispatch after leaving the block.
 class AstGraphBuilder::ControlScope::DeferredCommands : public ZoneObject {
  public:
   explicit DeferredCommands(AstGraphBuilder* owner)
@@ skipping 55 matching lines @@
   AstGraphBuilder* owner_;
   ZoneVector<Entry> deferred_;
 };
 
 
 // Control scope implementation for a BreakableStatement.
 class AstGraphBuilder::ControlScopeForBreakable : public ControlScope {
  public:
   ControlScopeForBreakable(AstGraphBuilder* owner, BreakableStatement* target,
                            ControlBuilder* control)
-      : ControlScope(owner, 0), target_(target), control_(control) {}
+      : ControlScope(owner), target_(target), control_(control) {}
 
  protected:
   virtual bool Execute(Command cmd, Statement* target, Node* value) OVERRIDE {
     if (target != target_) return false;  // We are not the command target.
     switch (cmd) {
       case CMD_BREAK:
         control_->Break();
         return true;
       case CMD_CONTINUE:
       case CMD_THROW:
       case CMD_RETURN:
         break;
     }
     return false;
   }
 
  private:
   BreakableStatement* target_;
   ControlBuilder* control_;
 };
 
 
 // Control scope implementation for an IterationStatement.
 class AstGraphBuilder::ControlScopeForIteration : public ControlScope {
  public:
   ControlScopeForIteration(AstGraphBuilder* owner, IterationStatement* target,
-                           LoopBuilder* control, int stack_delta)
-      : ControlScope(owner, stack_delta), target_(target), control_(control) {}
+                           LoopBuilder* control)
+      : ControlScope(owner), target_(target), control_(control) {}
 
  protected:
   virtual bool Execute(Command cmd, Statement* target, Node* value) OVERRIDE {
     if (target != target_) return false;  // We are not the command target.
     switch (cmd) {
       case CMD_BREAK:
         control_->Break();
         return true;
       case CMD_CONTINUE:
         control_->Continue();
         return true;
       case CMD_THROW:
       case CMD_RETURN:
         break;
     }
     return false;
   }
 
  private:
   BreakableStatement* target_;
   LoopBuilder* control_;
 };
 
 
 // Control scope implementation for a TryCatchStatement.
 class AstGraphBuilder::ControlScopeForCatch : public ControlScope {
  public:
   ControlScopeForCatch(AstGraphBuilder* owner, TryCatchBuilder* control)
-      : ControlScope(owner, 0), control_(control) {
+      : ControlScope(owner), control_(control) {
     builder()->try_nesting_level_++;  // Increment nesting.
   }
   ~ControlScopeForCatch() {
     builder()->try_nesting_level_--;  // Decrement nesting.
   }
 
  protected:
   virtual bool Execute(Command cmd, Statement* target, Node* value) OVERRIDE {
     switch (cmd) {
       case CMD_THROW:
@@ skipping 10 matching lines @@
  private:
   TryCatchBuilder* control_;
 };
 
 
 // Control scope implementation for a TryFinallyStatement.
 class AstGraphBuilder::ControlScopeForFinally : public ControlScope {
  public:
   ControlScopeForFinally(AstGraphBuilder* owner, DeferredCommands* commands,
                          TryFinallyBuilder* control)
-      : ControlScope(owner, 0), commands_(commands), control_(control) {
+      : ControlScope(owner), commands_(commands), control_(control) {
     builder()->try_nesting_level_++;  // Increment nesting.
   }
   ~ControlScopeForFinally() {
     builder()->try_nesting_level_--;  // Decrement nesting.
   }
 
  protected:
   virtual bool Execute(Command cmd, Statement* target, Node* value) OVERRIDE {
     Node* token = commands_->RecordCommand(cmd, target, value);
     control_->LeaveTry(token);
@@ skipping 48 matching lines @@
 
 
 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);
 
+  // Initialize control scope.
+  ControlScope control(this);
+
   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);
 
@@ skipping 226 matching lines @@
   return execution_context_->context();
 }
 
 
 void AstGraphBuilder::ControlScope::PerformCommand(Command command,
                                                    Statement* target,
                                                    Node* value) {
   Environment* env = environment()->CopyAsUnreachable();
   ControlScope* current = this;
   while (current != NULL) {
+    int stack_delta = environment()->stack_height() - current->stack_height();
+    if (stack_delta > 0) environment()->Drop(stack_delta);

[titzer, 2015/02/19 12:33:00]

environment()->TrimStack() ?

[Michael Starzinger, 2015/02/19 12:58:21]

Done. Called it just "Trim" as per offline discussion.

     if (current->Execute(command, target, value)) break;
-    environment()->Drop(current->stack_delta());
     current = current->outer_;
   }
   builder()->set_environment(env);
   DCHECK(current != NULL);  // Always handled (unless stack is malformed).
 }
 
 
 void AstGraphBuilder::ControlScope::BreakTo(BreakableStatement* stmt) {
   PerformCommand(CMD_BREAK, stmt, nullptr);
 }
@@ skipping 293 matching lines @@
     compare_switch.EndCase();
   }
 
   compare_switch.EndSwitch();
 }
 
 
 void AstGraphBuilder::VisitDoWhileStatement(DoWhileStatement* stmt) {
   LoopBuilder while_loop(this);
   while_loop.BeginLoop(GetVariablesAssignedInLoop(stmt), CheckOsrEntry(stmt));
-  VisitIterationBody(stmt, &while_loop, 0);
+  VisitIterationBody(stmt, &while_loop);
   while_loop.EndBody();
   VisitForTest(stmt->cond());
   Node* condition = environment()->Pop();
   while_loop.BreakUnless(condition);
   while_loop.EndLoop();
 }
 
 
 void AstGraphBuilder::VisitWhileStatement(WhileStatement* stmt) {
   LoopBuilder while_loop(this);
   while_loop.BeginLoop(GetVariablesAssignedInLoop(stmt), CheckOsrEntry(stmt));
   VisitForTest(stmt->cond());
   Node* condition = environment()->Pop();
   while_loop.BreakUnless(condition);
-  VisitIterationBody(stmt, &while_loop, 0);
+  VisitIterationBody(stmt, &while_loop);
   while_loop.EndBody();
   while_loop.EndLoop();
 }
 
 
 void AstGraphBuilder::VisitForStatement(ForStatement* stmt) {
   LoopBuilder for_loop(this);
   VisitIfNotNull(stmt->init());
   for_loop.BeginLoop(GetVariablesAssignedInLoop(stmt), CheckOsrEntry(stmt));
   if (stmt->cond() != NULL) {
     VisitForTest(stmt->cond());
     Node* condition = environment()->Pop();
     for_loop.BreakUnless(condition);
   } else {
     for_loop.BreakUnless(jsgraph()->TrueConstant());
   }
-  VisitIterationBody(stmt, &for_loop, 0);
+  VisitIterationBody(stmt, &for_loop);
   for_loop.EndBody();
   VisitIfNotNull(stmt->next());
   for_loop.EndLoop();
 }
 
 
 // TODO(dcarney): this is a big function.  Try to clean up some.
 void AstGraphBuilder::VisitForInStatement(ForInStatement* stmt) {
   VisitForValue(stmt->subject());
   Node* obj = environment()->Pop();
@@ skipping 118 matching lines @@
       is_property_missing.End();
     }
     // Replace 'value' in environment.
     environment()->Push(res);
     test_should_filter.Else();
     test_should_filter.End();
   }
   value = environment()->Pop();
   // Bind value and do loop body.
   VisitForInAssignment(stmt->each(), value, stmt->AssignmentId());
-  VisitIterationBody(stmt, &for_loop, 5);
+  VisitIterationBody(stmt, &for_loop);
   for_loop.EndBody();
   // Inc counter and continue.
   Node* index_inc =
       NewNode(javascript()->Add(), index, jsgraph()->OneConstant());
   // TODO(jarin): provide real bailout id.
   PrepareFrameState(index_inc, BailoutId::None());
   environment()->Poke(0, index_inc);
   for_loop.EndLoop();
   environment()->Drop(5);
   // PrepareForBailoutForId(stmt->ExitId(), NO_REGISTERS);
 }
 
 
 void AstGraphBuilder::VisitForOfStatement(ForOfStatement* stmt) {
   LoopBuilder for_loop(this);
   VisitForEffect(stmt->assign_iterator());
   for_loop.BeginLoop(GetVariablesAssignedInLoop(stmt), CheckOsrEntry(stmt));
   VisitForEffect(stmt->next_result());
   VisitForTest(stmt->result_done());
   Node* condition = environment()->Pop();
   for_loop.BreakWhen(condition);
   VisitForEffect(stmt->assign_each());
-  VisitIterationBody(stmt, &for_loop, 0);
+  VisitIterationBody(stmt, &for_loop);
   for_loop.EndBody();
   for_loop.EndLoop();
 }
 
 
 void AstGraphBuilder::VisitTryCatchStatement(TryCatchStatement* stmt) {
   TryCatchBuilder try_control(this);
 
   // Evaluate the try-block inside a control scope. This simulates a handler
   // that is intercepting 'throw' control commands.
@@ skipping 1069 matching lines @@
 }
 
 
 void AstGraphBuilder::VisitIfNotNull(Statement* stmt) {
   if (stmt == NULL) return;
   Visit(stmt);
 }
 
 
 void AstGraphBuilder::VisitIterationBody(IterationStatement* stmt,
-                                         LoopBuilder* loop, int stack_delta) {
-  ControlScopeForIteration scope(this, stmt, loop, stack_delta);
+                                         LoopBuilder* loop) {
+  ControlScopeForIteration scope(this, stmt, loop);
   Visit(stmt->body());
 }
 
 
 void AstGraphBuilder::VisitDelete(UnaryOperation* expr) {
   Node* value;
   if (expr->expression()->IsVariableProxy()) {
     // Delete of an unqualified identifier is only allowed in classic mode but
     // deleting "this" is allowed in all language modes.
     Variable* variable = expr->expression()->AsVariableProxy()->var();
@@ skipping 700 matching lines @@
     }
     if (!environment()->IsMarkedAsUnreachable()) {
       // Update the current control dependency for control-producing nodes.
       if (NodeProperties::IsControl(result)) {
         environment_->UpdateControlDependency(result);
       }
       // Add implicit exception continuation for throwing nodes.
       if (!result->op()->HasProperty(Operator::kNoThrow) && inside_try_scope) {
         Node* on_exception = graph()->NewNode(common()->IfException(), result);
         environment_->UpdateControlDependency(on_exception);
-        if (FLAG_turbo_exceptions) {
-          execution_control()->ThrowValue(jsgraph()->UndefinedConstant());
-        }
+        execution_control()->ThrowValue(jsgraph()->UndefinedConstant());
       }
       // Add implicit success continuation for throwing nodes.
       if (!result->op()->HasProperty(Operator::kNoThrow)) {
         Node* on_success = graph()->NewNode(common()->IfSuccess(), result);
         environment_->UpdateControlDependency(on_success);
       }
     }
   }
 
   return result;
@@ skipping 159 matching lines @@
     // Phi does not exist yet, introduce one.
     value = NewPhi(inputs, value, control);
     value->ReplaceInput(inputs - 1, other);
   }
   return value;
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8