Add static analysis to AST expressions that records whether a negative zero...

Add static analysis to AST expressions that records whether a negative zero will be treated identically to a positive zero in the expression's context.  Use this flag to avoid some tests in inlined smi code.
Review URL: http://codereview.chromium.org/965001

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4130 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/ast.h

@@ -251,6 +251,14 @@ class Expression: public AstNode {
     bitfields_ |= SideEffectFreeField::encode(is_side_effect_free);
   }
 
+  // Will the use of this expression treat -0 the same as 0 in all cases?
+  // If so, we can return 0 instead of -0 if we want to, to optimize code.
+  bool no_negative_zero() { return NoNegativeZeroField::decode(bitfields_); }
+  void set_no_negative_zero(bool no_negative_zero) {
+    bitfields_ &= ~NoNegativeZeroField::mask();
+    bitfields_ |= NoNegativeZeroField::encode(no_negative_zero);
+  }
+
   // Will ToInt32 (ECMA 262-3 9.5) or ToUint32 (ECMA 262-3 9.6)
   // be applied to the value of this expression?
   // If so, we may be able to optimize the calculation of the value.
@@ -270,7 +278,8 @@ class Expression: public AstNode {
 
   // Using template BitField<type, start, size>.
   class SideEffectFreeField : public BitField<bool, 0, 1> {};
-  class ToInt32Field : public BitField<bool, 1, 1> {};
+  class NoNegativeZeroField : public BitField<bool, 1, 1> {};
+  class ToInt32Field : public BitField<bool, 2, 1> {};
 };
 
 

src/ia32/codegen-ia32.h

@@ -469,7 +469,8 @@ class CodeGenerator: public AstVisitor {
   void GenericBinaryOperation(
       Token::Value op,
       StaticType* type,
-      OverwriteMode overwrite_mode);
+      OverwriteMode overwrite_mode,
+      bool no_negative_zero);
 
   // If possible, combine two constant smi values using op to produce
   // a smi result, and push it on the virtual frame, all at compile time.
@@ -483,7 +484,8 @@ class CodeGenerator: public AstVisitor {
                                     Handle<Object> constant_operand,
                                     StaticType* type,
                                     bool reversed,
-                                    OverwriteMode overwrite_mode);
+                                    OverwriteMode overwrite_mode,
+                                    bool no_negative_zero);
 
   // Emit code to perform a binary operation on two likely smis.
   // The code to handle smi arguments is produced inline.
@@ -491,7 +493,8 @@ class CodeGenerator: public AstVisitor {
   Result LikelySmiBinaryOperation(Token::Value op,
                                   Result* left,
                                   Result* right,
-                                  OverwriteMode overwrite_mode);
+                                  OverwriteMode overwrite_mode,
+                                  bool no_negative_zero);
 
   void Comparison(AstNode* node,
                   Condition cc,

src/rewriter.cc

@@ -220,6 +220,7 @@ void AstOptimizer::VisitFunctionBoilerplateLiteral(
 
 
 void AstOptimizer::VisitConditional(Conditional* node) {
+  node->condition()->set_no_negative_zero(true);
   Visit(node->condition());
   Visit(node->then_expression());
   Visit(node->else_expression());
@@ -319,6 +320,7 @@ void AstOptimizer::VisitAssignment(Assignment* node) {
       node->type()->SetAsLikelySmiIfUnknown();
       node->target()->type()->SetAsLikelySmiIfUnknown();
       node->value()->type()->SetAsLikelySmiIfUnknown();
+      node->value()->set_no_negative_zero(true);
       break;
     case Token::ASSIGN_ADD:
     case Token::ASSIGN_SUB:
@@ -393,6 +395,7 @@ void AstOptimizer::VisitThrow(Throw* node) {
 
 
 void AstOptimizer::VisitProperty(Property* node) {
+  node->key()->set_no_negative_zero(true);
   Visit(node->obj());
   Visit(node->key());
 }
@@ -422,6 +425,11 @@ void AstOptimizer::VisitCallRuntime(CallRuntime* node) {
 
 
 void AstOptimizer::VisitUnaryOperation(UnaryOperation* node) {
+  if (node->op() == Token::ADD || node->op() == Token::SUB) {
+    node->expression()->set_no_negative_zero(node->no_negative_zero());
+  } else {
+    node->expression()->set_no_negative_zero(true);
+  }
   Visit(node->expression());
   if (FLAG_safe_int32_compiler) {
     switch (node->op()) {
@@ -449,6 +457,9 @@ void AstOptimizer::VisitUnaryOperation(UnaryOperation* node) {
 
 void AstOptimizer::VisitCountOperation(CountOperation* node) {
   // Count operations assume that they work on Smis.
+  node->expression()->set_no_negative_zero(node->is_prefix() ?
+                                           true :
+                                           node->no_negative_zero());
   node->type()->SetAsLikelySmiIfUnknown();
   node->expression()->type()->SetAsLikelySmiIfUnknown();
   Visit(node->expression());
@@ -461,7 +472,12 @@ void AstOptimizer::VisitBinaryOperation(BinaryOperation* node) {
   switch (node->op()) {
     case Token::COMMA:
     case Token::OR:
+      node->left()->set_no_negative_zero(true);
+      node->right()->set_no_negative_zero(node->no_negative_zero());
+      break;
     case Token::AND:
+      node->left()->set_no_negative_zero(node->no_negative_zero());
+      node->right()->set_no_negative_zero(node->no_negative_zero());
       break;
     case Token::BIT_OR:
     case Token::BIT_XOR:
@@ -474,6 +490,8 @@ void AstOptimizer::VisitBinaryOperation(BinaryOperation* node) {
       node->right()->type()->SetAsLikelySmiIfUnknown();
       node->left()->set_to_int32(true);
       node->right()->set_to_int32(true);
+      node->left()->set_no_negative_zero(true);
+      node->right()->set_no_negative_zero(true);
       break;
     case Token::ADD:
     case Token::SUB:
@@ -484,6 +502,13 @@ void AstOptimizer::VisitBinaryOperation(BinaryOperation* node) {
         node->left()->type()->SetAsLikelySmiIfUnknown();
         node->right()->type()->SetAsLikelySmiIfUnknown();
       }
+      node->left()->set_no_negative_zero(node->no_negative_zero());
+      node->right()->set_no_negative_zero(node->no_negative_zero());
+      if (node->op() == Token::DIV) {
+        node->right()->set_no_negative_zero(false);
+      } else if (node->op() == Token::MOD) {
+        node->right()->set_no_negative_zero(true);
+      }
       break;
     default:
       UNREACHABLE();
@@ -551,6 +576,10 @@ void AstOptimizer::VisitCompareOperation(CompareOperation* node) {
     node->right()->type()->SetAsLikelySmiIfUnknown();
   }
 
+  node->left()->set_no_negative_zero(true);
+  // Only [[HasInstance]] has the right argument passed unchanged to it.
+  node->right()->set_no_negative_zero(true);
+
   Visit(node->left());
   Visit(node->right());