CSE2410 Fall 2014 Bounce

// Copyright 2012 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 "rewriter.h"

#include "ast.h"

#include "compiler.h"

#include "scopes.h"

namespace v8 {

namespace internal {

class Processor: public AstVisitor {

 public:

  Processor(Variable* result, Zone* zone)

      : result_(result),

        result_assigned_(false),

        is_set_(false),

        in_try_(false),

        factory_(zone->isolate(), zone) {

    InitializeAstVisitor(zone->isolate());

  }

  virtual ~Processor() { }

  void Process(ZoneList<Statement*>* statements);

  bool result_assigned() const { return result_assigned_; }

  AstNodeFactory<AstNullVisitor>* factory() {

    return &factory_;

  }

 private:

  Variable* result_;

  // We are not tracking result usage via the result_'s use

  // counts (we leave the accurate computation to the

  // usage analyzer). Instead we simple remember if

  // there was ever an assignment to result_.

  bool result_assigned_;

  // To avoid storing to .result all the time, we eliminate some of

  // the stores by keeping track of whether or not we're sure .result

  // will be overwritten anyway. This is a bit more tricky than what I

  // was hoping for

  bool is_set_;

  bool in_try_;

  AstNodeFactory<AstNullVisitor> factory_;

  Expression* SetResult(Expression* value) {

    result_assigned_ = true;

    VariableProxy* result_proxy = factory()->NewVariableProxy(result_);

    return factory()->NewAssignment(

        Token::ASSIGN, result_proxy, value, RelocInfo::kNoPosition);

  }

  // Node visitors.

#define DEF_VISIT(type) \

  virtual void Visit##type(type* node);

  AST_NODE_LIST(DEF_VISIT)

#undef DEF_VISIT

  void VisitIterationStatement(IterationStatement* stmt);

  DEFINE_AST_VISITOR_SUBCLASS_MEMBERS();

};

void Processor::Process(ZoneList<Statement*>* statements) {

  for (int i = statements->length() - 1; i >= 0; --i) {

    Visit(statements->at(i));

  }

}

void Processor::VisitBlock(Block* node) {

  // An initializer block is the rewritten form of a variable declaration

  // with initialization expressions. The initializer block contains the

  // list of assignments corresponding to the initialization expressions.

  // While unclear from the spec (ECMA-262, 3rd., 12.2), the value of

  // a variable declaration with initialization expression is 'undefined'

  // with some JS VMs: For instance, using smjs, print(eval('var x = 7'))

  // returns 'undefined'. To obtain the same behavior with v8, we need

  // to prevent rewriting in that case.

  if (!node->is_initializer_block()) Process(node->statements());

}

void Processor::VisitModuleStatement(ModuleStatement* node) {

  bool set_after_body = is_set_;

  Visit(node->body());

  is_set_ = is_set_ && set_after_body;

}

void Processor::VisitExpressionStatement(ExpressionStatement* node) {

  // Rewrite : <x>; -> .result = <x>;

  if (!is_set_ && !node->expression()->IsThrow()) {

    node->set_expression(SetResult(node->expression()));

    if (!in_try_) is_set_ = true;

  }

}

void Processor::VisitIfStatement(IfStatement* node) {

  // Rewrite both then and else parts (reversed).

  bool save = is_set_;

  Visit(node->else_statement());

  bool set_after_then = is_set_;

  is_set_ = save;

  Visit(node->then_statement());

  is_set_ = is_set_ && set_after_then;

}

void Processor::VisitIterationStatement(IterationStatement* node) {

  // Rewrite the body.

  bool set_after_loop = is_set_;

  Visit(node->body());

  is_set_ = is_set_ && set_after_loop;

}

void Processor::VisitDoWhileStatement(DoWhileStatement* node) {

  VisitIterationStatement(node);

}

void Processor::VisitWhileStatement(WhileStatement* node) {

  VisitIterationStatement(node);

}

void Processor::VisitForStatement(ForStatement* node) {

  VisitIterationStatement(node);

}

void Processor::VisitForInStatement(ForInStatement* node) {

  VisitIterationStatement(node);

}

void Processor::VisitForOfStatement(ForOfStatement* node) {

  VisitIterationStatement(node);

}

void Processor::VisitTryCatchStatement(TryCatchStatement* node) {

  // Rewrite both try and catch blocks (reversed order).

  bool set_after_catch = is_set_;

  Visit(node->catch_block());

  is_set_ = is_set_ && set_after_catch;

  bool save = in_try_;

  in_try_ = true;

  Visit(node->try_block());

  in_try_ = save;

}

void Processor::VisitTryFinallyStatement(TryFinallyStatement* node) {

  // Rewrite both try and finally block (reversed order).

  Visit(node->finally_block());

  bool save = in_try_;

  in_try_ = true;

  Visit(node->try_block());

  in_try_ = save;

}

void Processor::VisitSwitchStatement(SwitchStatement* node) {

  // Rewrite statements in all case clauses in reversed order.

  ZoneList<CaseClause*>* clauses = node->cases();

  bool set_after_switch = is_set_;

  for (int i = clauses->length() - 1; i >= 0; --i) {

    CaseClause* clause = clauses->at(i);

    Process(clause->statements());

  }

  is_set_ = is_set_ && set_after_switch;

}

void Processor::VisitCaseClause(CaseClause* clause) {

  UNREACHABLE();

}

void Processor::VisitContinueStatement(ContinueStatement* node) {

  is_set_ = false;

}

void Processor::VisitBreakStatement(BreakStatement* node) {

  is_set_ = false;

}

void Processor::VisitWithStatement(WithStatement* node) {

  bool set_after_body = is_set_;

  Visit(node->statement());

  is_set_ = is_set_ && set_after_body;

}

// Do nothing:

void Processor::VisitVariableDeclaration(VariableDeclaration* node) {}

void Processor::VisitFunctionDeclaration(FunctionDeclaration* node) {}

void Processor::VisitModuleDeclaration(ModuleDeclaration* node) {}

void Processor::VisitImportDeclaration(ImportDeclaration* node) {}

void Processor::VisitExportDeclaration(ExportDeclaration* node) {}

void Processor::VisitModuleLiteral(ModuleLiteral* node) {}

void Processor::VisitModuleVariable(ModuleVariable* node) {}

void Processor::VisitModulePath(ModulePath* node) {}

void Processor::VisitModuleUrl(ModuleUrl* node) {}

void Processor::VisitEmptyStatement(EmptyStatement* node) {}

void Processor::VisitReturnStatement(ReturnStatement* node) {}

void Processor::VisitDebuggerStatement(DebuggerStatement* node) {}

// Expressions are never visited yet.

#define DEF_VISIT(type)                                         \

  void Processor::Visit##type(type* expr) { UNREACHABLE(); }

EXPRESSION_NODE_LIST(DEF_VISIT)

#undef DEF_VISIT

// Assumes code has been parsed.  Mutates the AST, so the AST should not

// continue to be used in the case of failure.

bool Rewriter::Rewrite(CompilationInfo* info) {

  FunctionLiteral* function = info->function();

  ASSERT(function != NULL);

  Scope* scope = function->scope();

  ASSERT(scope != NULL);

  if (!scope->is_global_scope() && !scope->is_eval_scope()) return true;

  ZoneList<Statement*>* body = function->body();

  if (!body->is_empty()) {

    Variable* result = scope->NewTemporary(

        info->isolate()->factory()->result_string());

    Processor processor(result, info->zone());

    processor.Process(body);

    if (processor.HasStackOverflow()) return false;

    if (processor.result_assigned()) {

      ASSERT(function->end_position() != RelocInfo::kNoPosition);

      // Set the position of the assignment statement one character past the

      // source code, such that it definitely is not in the source code range

      // of an immediate inner scope. For example in

      //   eval('with ({x:1}) x = 1');

      // the end position of the function generated for executing the eval code

      // coincides with the end of the with scope which is the position of '1'.

      int pos = function->end_position();

      VariableProxy* result_proxy = processor.factory()->NewVariableProxy(

          result->name(), false, result->interface(), pos);

      result_proxy->BindTo(result);

      Statement* result_statement =

          processor.factory()->NewReturnStatement(result_proxy, pos);

      body->Add(result_statement, info->zone());

    }

  }

  return true;

}

} }  // namespace v8::internal