Remove unneeded variable usage analysis.

src/usage-analyzer.cc

-// Copyright 2006-2008 the V8 project authors. All rights reserved.
-// Redistribution and use in source and binary forms, with or without
-// modification, are permitted provided that the following conditions are
-// met:
-//
-//     * Redistributions of source code must retain the above copyright
-//       notice, this list of conditions and the following disclaimer.
-//     * Redistributions in binary form must reproduce the above
-//       copyright notice, this list of conditions and the following
-//       disclaimer in the documentation and/or other materials provided
-//       with the distribution.
-//     * Neither the name of Google Inc. nor the names of its
-//       contributors may be used to endorse or promote products derived
-//       from this software without specific prior written permission.
-//
-// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
-// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
-// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
-// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
-// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
-// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
-// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
-// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
-// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
-// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
-// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
-
-#include "v8.h"
-
-#include "ast.h"
-#include "scopes.h"
-#include "usage-analyzer.h"
-
-namespace v8 {
-namespace internal {
-
-// Weight boundaries
-static const int MinWeight = 1;
-static const int MaxWeight = 1000000;
-static const int InitialWeight = 100;
-
-
-class UsageComputer: public AstVisitor {
- public:
-  static bool Traverse(AstNode* node);
-
-  // AST node visit functions.
-#define DECLARE_VISIT(type) void Visit##type(type* node);
-  AST_NODE_LIST(DECLARE_VISIT)
-#undef DECLARE_VISIT
-
-  void VisitVariable(Variable* var);
-
- private:
-  int weight_;
-  bool is_write_;
-
-  UsageComputer(int weight, bool is_write);
-  virtual ~UsageComputer();
-
-  // Helper functions
-  void RecordUses(UseCount* uses);
-  void Read(Expression* x);
-  void Write(Expression* x);
-  void ReadList(ZoneList<Expression*>* list);
-  void ReadList(ZoneList<ObjectLiteral::Property*>* list);
-
-  friend class WeightScaler;
-};
-
-
-class WeightScaler BASE_EMBEDDED {
- public:
-  WeightScaler(UsageComputer* uc, float scale);
-  ~WeightScaler();
-
- private:
-  UsageComputer* uc_;
-  int old_weight_;
-};
-
-
-// ----------------------------------------------------------------------------
-// Implementation of UsageComputer
-
-bool UsageComputer::Traverse(AstNode* node) {
-  UsageComputer uc(InitialWeight, false);
-  uc.Visit(node);
-  return !uc.HasStackOverflow();
-}
-
-
-void UsageComputer::VisitBlock(Block* node) {
-  VisitStatements(node->statements());
-}
-
-
-void UsageComputer::VisitDeclaration(Declaration* node) {
-  Write(node->proxy());
-  if (node->fun() != NULL)
-    VisitFunctionLiteral(node->fun());
-}
-
-
-void UsageComputer::VisitExpressionStatement(ExpressionStatement* node) {
-  Visit(node->expression());
-}
-
-
-void UsageComputer::VisitEmptyStatement(EmptyStatement* node) {
-  // nothing to do
-}
-
-
-void UsageComputer::VisitIfStatement(IfStatement* node) {
-  Read(node->condition());
-  { WeightScaler ws(this, 0.5);  // executed 50% of the time
-    Visit(node->then_statement());
-    Visit(node->else_statement());
-  }
-}
-
-
-void UsageComputer::VisitContinueStatement(ContinueStatement* node) {
-  // nothing to do
-}
-
-
-void UsageComputer::VisitBreakStatement(BreakStatement* node) {
-  // nothing to do
-}
-
-
-void UsageComputer::VisitReturnStatement(ReturnStatement* node) {
-  Read(node->expression());
-}
-
-
-void UsageComputer::VisitWithEnterStatement(WithEnterStatement* node) {
-  Read(node->expression());
-}
-
-
-void UsageComputer::VisitWithExitStatement(WithExitStatement* node) {
-  // nothing to do
-}
-
-
-void UsageComputer::VisitSwitchStatement(SwitchStatement* node) {
-  Read(node->tag());
-  ZoneList<CaseClause*>* cases = node->cases();
-  for (int i = cases->length(); i-- > 0;) {
-    WeightScaler ws(this, static_cast<float>(1.0 / cases->length()));
-    CaseClause* clause = cases->at(i);
-    if (!clause->is_default())
-      Read(clause->label());
-    VisitStatements(clause->statements());
-  }
-}
-
-
-void UsageComputer::VisitDoWhileStatement(DoWhileStatement* node) {
-  WeightScaler ws(this, 10.0);
-  Read(node->cond());
-  Visit(node->body());
-}
-
-
-void UsageComputer::VisitWhileStatement(WhileStatement* node) {
-  WeightScaler ws(this, 10.0);
-  Read(node->cond());
-  Visit(node->body());
-}
-
-
-void UsageComputer::VisitForStatement(ForStatement* node) {
-  if (node->init() != NULL) Visit(node->init());
-  { WeightScaler ws(this, 10.0);  // executed in each iteration
-    if (node->cond() != NULL) Read(node->cond());
-    if (node->next() != NULL) Visit(node->next());
-    Visit(node->body());
-  }
-}
-
-
-void UsageComputer::VisitForInStatement(ForInStatement* node) {
-  WeightScaler ws(this, 10.0);
-  Write(node->each());
-  Read(node->enumerable());
-  Visit(node->body());
-}
-
-
-void UsageComputer::VisitTryCatchStatement(TryCatchStatement* node) {
-  Visit(node->try_block());
-  { WeightScaler ws(this, 0.25);
-    Write(node->catch_var());
-    Visit(node->catch_block());
-  }
-}
-
-
-void UsageComputer::VisitTryFinallyStatement(TryFinallyStatement* node) {
-  Visit(node->try_block());
-  Visit(node->finally_block());
-}
-
-
-void UsageComputer::VisitDebuggerStatement(DebuggerStatement* node) {
-}
-
-
-void UsageComputer::VisitFunctionLiteral(FunctionLiteral* node) {
-  ZoneList<Declaration*>* decls = node->scope()->declarations();
-  for (int i = 0; i < decls->length(); i++) VisitDeclaration(decls->at(i));
-  VisitStatements(node->body());
-}
-
-
-void UsageComputer::VisitFunctionBoilerplateLiteral(
-    FunctionBoilerplateLiteral* node) {
-  // Do nothing.
-}
-
-
-void UsageComputer::VisitConditional(Conditional* node) {
-  Read(node->condition());
-  { WeightScaler ws(this, 0.5);
-    Read(node->then_expression());
-    Read(node->else_expression());
-  }
-}
-
-
-void UsageComputer::VisitSlot(Slot* node) {
-  UNREACHABLE();
-}
-
-
-void UsageComputer::VisitVariable(Variable* node) {
-  RecordUses(node->var_uses());
-}
-
-
-void UsageComputer::VisitVariableProxy(VariableProxy* node) {
-  // The proxy may refer to a variable in which case it was bound via
-  // VariableProxy::BindTo.
-  RecordUses(node->var_uses());
-}
-
-
-void UsageComputer::VisitLiteral(Literal* node) {
-  // nothing to do
-}
-
-void UsageComputer::VisitRegExpLiteral(RegExpLiteral* node) {
-  // nothing to do
-}
-
-
-void UsageComputer::VisitObjectLiteral(ObjectLiteral* node) {
-  ReadList(node->properties());
-}
-
-
-void UsageComputer::VisitArrayLiteral(ArrayLiteral* node) {
-  ReadList(node->values());
-}
-
-
-void UsageComputer::VisitCatchExtensionObject(CatchExtensionObject* node) {
-  Read(node->value());
-}
-
-
-void UsageComputer::VisitAssignment(Assignment* node) {
-  if (node->op() != Token::ASSIGN)
-    Read(node->target());
-  Write(node->target());
-  Read(node->value());
-}
-
-
-void UsageComputer::VisitThrow(Throw* node) {
-  Read(node->exception());
-}
-
-
-void UsageComputer::VisitProperty(Property* node) {
-  // In any case (read or write) we read both the
-  // node's object and the key.
-  Read(node->obj());
-  Read(node->key());
-  // If the node's object is a variable proxy,
-  // we have a 'simple' object property access. We count
-  // the access via the variable or proxy's object uses.
-  VariableProxy* proxy = node->obj()->AsVariableProxy();
-  if (proxy != NULL) {
-    RecordUses(proxy->obj_uses());
-  }
-}
-
-
-void UsageComputer::VisitCall(Call* node) {
-  Read(node->expression());
-  ReadList(node->arguments());
-}
-
-
-void UsageComputer::VisitCallNew(CallNew* node) {
-  Read(node->expression());
-  ReadList(node->arguments());
-}
-
-
-void UsageComputer::VisitCallRuntime(CallRuntime* node) {
-  ReadList(node->arguments());
-}
-
-
-void UsageComputer::VisitUnaryOperation(UnaryOperation* node) {
-  Read(node->expression());
-}
-
-
-void UsageComputer::VisitCountOperation(CountOperation* node) {
-  Read(node->expression());
-  Write(node->expression());
-}
-
-
-void UsageComputer::VisitBinaryOperation(BinaryOperation* node) {
-  Read(node->left());
-  Read(node->right());
-}
-
-
-void UsageComputer::VisitCompareOperation(CompareOperation* node) {
-  Read(node->left());
-  Read(node->right());
-}
-
-
-void UsageComputer::VisitThisFunction(ThisFunction* node) {
-}
-
-
-UsageComputer::UsageComputer(int weight, bool is_write) {
-  weight_ = weight;
-  is_write_ = is_write;
-}
-
-
-UsageComputer::~UsageComputer() {
-  // nothing to do
-}
-
-
-void UsageComputer::RecordUses(UseCount* uses) {
-  if (is_write_)
-    uses->RecordWrite(weight_);
-  else
-    uses->RecordRead(weight_);
-}
-
-
-void UsageComputer::Read(Expression* x) {
-  if (is_write_) {
-    UsageComputer uc(weight_, false);
-    uc.Visit(x);
-  } else {
-    Visit(x);
-  }
-}
-
-
-void UsageComputer::Write(Expression* x) {
-  if (!is_write_) {
-    UsageComputer uc(weight_, true);
-    uc.Visit(x);
-  } else {
-    Visit(x);
-  }
-}
-
-
-void UsageComputer::ReadList(ZoneList<Expression*>* list) {
-  for (int i = list->length(); i-- > 0; )
-    Read(list->at(i));
-}
-
-
-void UsageComputer::ReadList(ZoneList<ObjectLiteral::Property*>* list) {
-  for (int i = list->length(); i-- > 0; )
-    Read(list->at(i)->value());
-}
-
-
-// ----------------------------------------------------------------------------
-// Implementation of WeightScaler
-
-WeightScaler::WeightScaler(UsageComputer* uc, float scale) {
-  uc_ = uc;
-  old_weight_ = uc->weight_;
-  int new_weight = static_cast<int>(uc->weight_ * scale);
-  if (new_weight <= 0) new_weight = MinWeight;
-  else if (new_weight > MaxWeight) new_weight = MaxWeight;
-  uc->weight_ = new_weight;
-}
-
-
-WeightScaler::~WeightScaler() {
-  uc_->weight_ = old_weight_;
-}
-
-
-// ----------------------------------------------------------------------------
-// Interface to variable usage analysis
-
-bool AnalyzeVariableUsage(FunctionLiteral* lit) {
-  if (!FLAG_usage_computation) return true;
-  HistogramTimerScope timer(&Counters::usage_analysis);
-  return UsageComputer::Traverse(lit);
-}
-
-} }  // namespace v8::internal