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

src/ast.h

 // Copyright 2010 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
@@ skipping 233 matching lines @@
   // AST analysis results
 
   // True if the expression rooted at this node can be compiled by the
   // side-effect free compiler.
   bool side_effect_free() { return SideEffectFreeField::decode(bitfields_); }
   void set_side_effect_free(bool is_side_effect_free) {
     bitfields_ &= ~SideEffectFreeField::mask();
     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.
   bool to_int32() { return ToInt32Field::decode(bitfields_); }
   void set_to_int32(bool to_int32) {
     bitfields_ &= ~ToInt32Field::mask();
     bitfields_ |= ToInt32Field::encode(to_int32);
   }
 
 
  private:
   uint32_t bitfields_;
   StaticType type_;
 
   DefinitionInfo* def_;
   ZoneList<DefinitionInfo*>* defined_vars_;
 
   // 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> {};
 };
 
 
 /**
  * A sentinel used during pre parsing that represents some expression
  * that is a valid left hand side without having to actually build
  * the expression.
  */
 class ValidLeftHandSideSentinel: public Expression {
  public:
@@ skipping 1695 matching lines @@
 #undef DEF_VISIT
 
  private:
   bool stack_overflow_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_AST_H_