Speed up compares with characters ie single-character strings.

Make use of it when we know that something can't be a NaN.
Review URL: http://codereview.chromium.org/524059

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@3566 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/arm/codegen-arm.cc

@@ -44,7 +44,8 @@ namespace internal {
 
 static void EmitIdenticalObjectComparison(MacroAssembler* masm,
                                           Label* slow,
-                                          Condition cc);
+                                          Condition cc,
+                                          bool never_nan_nan);
 static void EmitSmiNonsmiComparison(MacroAssembler* masm,
                                     Label* rhs_not_nan,
                                     Label* slow,
@@ -4598,17 +4599,21 @@ void WriteInt32ToHeapNumberStub::Generate(MacroAssembler* masm) {
 // for "identity and not NaN".
 static void EmitIdenticalObjectComparison(MacroAssembler* masm,
                                           Label* slow,
-                                          Condition cc) {
+                                          Condition cc,
+                                          bool never_nan_nan) {
   Label not_identical;
+  Label heap_number, return_equal;
+  Register exp_mask_reg = r5;
   __ cmp(r0, Operand(r1));
   __ b(ne, &not_identical);
 
-  Register exp_mask_reg = r5;
+  // The two objects are identical.  If we know that one of them isn't NaN then
+  // we now know they test equal.
+  if (cc != eq || !never_nan_nan) {
     __ mov(exp_mask_reg, Operand(HeapNumber::kExponentMask));
 
     // Test for NaN. Sadly, we can't just compare to Factory::nan_value(),
     // so we do the second best thing - test it ourselves.
-  Label heap_number, return_equal;
     // They are both equal and they are not both Smis so both of them are not
     // Smis.  If it's not a heap number, then return equal.
     if (cc == lt || cc == gt) {
@@ -4622,8 +4627,8 @@ static void EmitIdenticalObjectComparison(MacroAssembler* masm,
         __ cmp(r4, Operand(FIRST_JS_OBJECT_TYPE));
         __ b(ge, slow);
         // Normally here we fall through to return_equal, but undefined is
-      // special: (undefined == undefined) == true, but (undefined <= undefined)
-      // == false!  See ECMAScript 11.8.5.
+        // special: (undefined == undefined) == true, but
+        // (undefined <= undefined) == false!  See ECMAScript 11.8.5.
         if (cc == le || cc == ge) {
           __ cmp(r4, Operand(ODDBALL_TYPE));
           __ b(ne, &return_equal);
@@ -4631,14 +4636,18 @@ static void EmitIdenticalObjectComparison(MacroAssembler* masm,
           __ cmp(r0, Operand(r2));
           __ b(ne, &return_equal);
           if (cc == le) {
-          __ mov(r0, Operand(GREATER));  // undefined <= undefined should fail.
+            // undefined <= undefined should fail.
+            __ mov(r0, Operand(GREATER));
           } else  {
-          __ mov(r0, Operand(LESS));     // undefined >= undefined should fail.
+            // undefined >= undefined should fail.
+            __ mov(r0, Operand(LESS));
           }
           __ mov(pc, Operand(lr));       // Return.
         }
       }
     }
+  }
+
   __ bind(&return_equal);
   if (cc == lt) {
     __ mov(r0, Operand(GREATER));  // Things aren't less than themselves.
@@ -4649,6 +4658,7 @@ static void EmitIdenticalObjectComparison(MacroAssembler* masm,
   }
   __ mov(pc, Operand(lr));  // Return.
 
+  if (cc != eq || !never_nan_nan) {
     // For less and greater we don't have to check for NaN since the result of
     // x < x is false regardless.  For the others here is some code to check
     // for NaN.
@@ -4686,6 +4696,7 @@ static void EmitIdenticalObjectComparison(MacroAssembler* masm,
       __ mov(pc, Operand(lr));  // Return.
     }
     // No fall through here.
+ }
 
   __ bind(&not_identical);
 }
@@ -4885,6 +4896,14 @@ static void EmitStrictTwoHeapObjectCompare(MacroAssembler* masm) {
     // Check for oddballs: true, false, null, undefined.
     __ cmp(r3, Operand(ODDBALL_TYPE));
     __ b(eq, &return_not_equal);
+
+    // Now that we have the types we might as well check for symbol-symbol.
+    // Ensure that no non-strings have the symbol bit set.
+    ASSERT(kNotStringTag + kIsSymbolMask > LAST_TYPE);
+    ASSERT(kSymbolTag != 0);
+    __ and_(r2, r2, Operand(r3));
+    __ tst(r2, Operand(kIsSymbolMask));
+    __ b(ne, &return_not_equal);
 }
 
 
@@ -4911,12 +4930,13 @@ static void EmitCheckForTwoHeapNumbers(MacroAssembler* masm,
 // Fast negative check for symbol-to-symbol equality.
 static void EmitCheckForSymbols(MacroAssembler* masm, Label* slow) {
   // r2 is object type of r0.
-  __ tst(r2, Operand(kIsNotStringMask));
-  __ b(ne, slow);
+  // Ensure that no non-strings have the symbol bit set.
+  ASSERT(kNotStringTag + kIsSymbolMask > LAST_TYPE);
+  ASSERT(kSymbolTag != 0);
   __ tst(r2, Operand(kIsSymbolMask));
   __ b(eq, slow);
-  __ CompareObjectType(r1, r3, r3, FIRST_NONSTRING_TYPE);
-  __ b(ge, slow);
+  __ ldr(r3, FieldMemOperand(r1, HeapObject::kMapOffset));
+  __ ldrb(r3, FieldMemOperand(r3, Map::kInstanceTypeOffset));
   __ tst(r3, Operand(kIsSymbolMask));
   __ b(eq, slow);
 
@@ -4938,7 +4958,7 @@ void CompareStub::Generate(MacroAssembler* masm) {
 
   // Handle the case where the objects are identical.  Either returns the answer
   // or goes to slow.  Only falls through if the objects were not identical.
-  EmitIdenticalObjectComparison(masm, &slow, cc_);
+  EmitIdenticalObjectComparison(masm, &slow, cc_, never_nan_nan_);
 
   // If either is a Smi (we know that not both are), then they can only
   // be strictly equal if the other is a HeapNumber.
@@ -5002,7 +5022,9 @@ void CompareStub::Generate(MacroAssembler* masm) {
                              &slow);
 
   __ bind(&check_for_symbols);
-  if (cc_ == eq) {
+  // In the strict case the EmitStrictTwoHeapObjectCompare already took care of
+  // symbols.
+  if (cc_ == eq && !strict_) {
     // Either jumps to slow or returns the answer.  Assumes that r2 is the type
     // of r0 on entry.
     EmitCheckForSymbols(masm, &slow);
@@ -6487,10 +6509,53 @@ void CallFunctionStub::Generate(MacroAssembler* masm) {
 }
 
 
+const char* CompareStub::GetName() {
+  switch(cc_) {
+    case lt: return "CompareStub_LT";
+    case gt: return "CompareStub_GT";
+    case le: return "CompareStub_LE";
+    case ge: return "CompareStub_GE";
+    case ne: {
+      if (strict_) {
+        if (never_nan_nan_) {
+          return "CompareStub_NE_STRICT_NO_NAN";
+        } else {
+          return "CompareStub_NE_STRICT";
+        }
+      } else {
+        if (never_nan_nan_) {
+          return "CompareStub_NE_NO_NAN";
+        } else {
+          return "CompareStub_NE";
+        }
+      }
+    }
+    case eq: {
+      if (strict_) {
+        if (never_nan_nan_) {
+          return "CompareStub_EQ_STRICT_NO_NAN";
+        } else {
+          return "CompareStub_EQ_STRICT";
+        }
+      } else {
+        if (never_nan_nan_) {
+          return "CompareStub_EQ_NO_NAN";
+        } else {
+          return "CompareStub_EQ";
+        }
+      }
+    }
+    default: return "CompareStub";
+  }
+}
+
+
 int CompareStub::MinorKey() {
-  // Encode the two parameters in a unique 16 bit value.
-  ASSERT(static_cast<unsigned>(cc_) >> 28 < (1 << 15));
-  return (static_cast<unsigned>(cc_) >> 27) | (strict_ ? 1 : 0);
+  // Encode the three parameters in a unique 16 bit value.
+  ASSERT(static_cast<unsigned>(cc_) < (1 << 14));
+  int nnn_value = (never_nan_nan_ ? 2 : 0);
+  if (cc_ != eq) nnn_value = 0;  // Avoid duplicate stubs.
+  return (static_cast<unsigned>(cc_) >> 26) | nnn_value | (strict_ ? 1 : 0);
 }
 
 

src/codegen.h

@@ -317,15 +317,30 @@ class GenericUnaryOpStub : public CodeStub {
 };
 
 
+enum NaNInformation {
+  kBothCouldBeNaN,
+  kCantBothBeNaN
+};
+
+
 class CompareStub: public CodeStub {
  public:
-  CompareStub(Condition cc, bool strict) : cc_(cc), strict_(strict) { }
+  CompareStub(Condition cc,
+              bool strict,
+              NaNInformation nan_info = kBothCouldBeNaN) :
+      cc_(cc), strict_(strict), never_nan_nan_(nan_info == kCantBothBeNaN) { }
 
   void Generate(MacroAssembler* masm);
 
  private:
   Condition cc_;
   bool strict_;
+  // Only used for 'equal' comparisons.  Tells the stub that we already know
+  // that at least one side of the comparison is not NaN.  This allows the
+  // stub to use object identity in the positive case.  We ignore it when
+  // generating the minor key for other comparisons to avoid creating more
+  // stubs.
+  bool never_nan_nan_;
 
   Major MajorKey() { return Compare; }
 
@@ -337,6 +352,9 @@ class CompareStub: public CodeStub {
                          Register object,
                          Register scratch);
 
+  // Unfortunately you have to run without snapshots to see most of these
+  // names in the profile since most compare stubs end up in the snapshot.
+  const char* GetName();
 #ifdef DEBUG
   void Print() {
     PrintF("CompareStub (cc %d), (strict %s)\n",

src/ia32/codegen-ia32.cc

@@ -1899,6 +1899,13 @@ void CodeGenerator::ConstantSmiBinaryOperation(Token::Value op,
 }
 
 
+static bool CouldBeNaN(const Result& result) {
+  if (!result.is_constant()) return true;
+  if (!result.handle()->IsHeapNumber()) return false;
+  return isnan(HeapNumber::cast(*result.handle())->value());
+}
+
+
 void CodeGenerator::Comparison(AstNode* node,
                                Condition cc,
                                bool strict,
@@ -1919,15 +1926,28 @@ void CodeGenerator::Comparison(AstNode* node,
   }
   ASSERT(cc == less || cc == equal || cc == greater_equal);
 
-  // If either side is a constant smi, optimize the comparison.
-  bool left_side_constant_smi =
-      left_side.is_constant() && left_side.handle()->IsSmi();
-  bool right_side_constant_smi =
-      right_side.is_constant() && right_side.handle()->IsSmi();
-  bool left_side_constant_null =
-      left_side.is_constant() && left_side.handle()->IsNull();
-  bool right_side_constant_null =
-      right_side.is_constant() && right_side.handle()->IsNull();
+  // If either side is a constant of some sort, we can probably optimize the
+  // comparison.
+  bool left_side_constant_smi = false;
+  bool left_side_constant_null = false;
+  bool left_side_constant_1_char_string = false;
+  if (left_side.is_constant()) {
+    left_side_constant_smi = left_side.handle()->IsSmi();
+    left_side_constant_null = left_side.handle()->IsNull();
+    left_side_constant_1_char_string = 
+        (left_side.handle()->IsString() &&
+         (String::cast(*left_side.handle())->length() == 1));
+  }
+  bool right_side_constant_smi = false;
+  bool right_side_constant_null = false;
+  bool right_side_constant_1_char_string = false;
+  if (right_side.is_constant()) {
+    right_side_constant_smi = right_side.handle()->IsSmi();
+    right_side_constant_null = right_side.handle()->IsNull();
+    right_side_constant_1_char_string = 
+        (right_side.handle()->IsString() &&
+         (String::cast(*right_side.handle())->length() == 1));
+  }
 
   if (left_side_constant_smi || right_side_constant_smi) {
     if (left_side_constant_smi && right_side_constant_smi) {
@@ -2016,7 +2036,7 @@ void CodeGenerator::Comparison(AstNode* node,
       }
 
       // Setup and call the compare stub.
-      CompareStub stub(cc, strict);
+      CompareStub stub(cc, strict, kCantBothBeNaN);
       Result result = frame_->CallStub(&stub, &left_side, &right_side);
       result.ToRegister();
       __ cmp(result.reg(), 0);
@@ -2075,18 +2095,150 @@ void CodeGenerator::Comparison(AstNode* node,
       operand.Unuse();
       dest->Split(not_zero);
     }
+  } else if (left_side_constant_1_char_string ||
+             right_side_constant_1_char_string) {
+    if (left_side_constant_1_char_string && right_side_constant_1_char_string) {
+      // Trivial case, comparing two constants.
+      int left_value = String::cast(*left_side.handle())->Get(0);
+      int right_value = String::cast(*right_side.handle())->Get(0);
+      switch (cc) {
+        case less:
+          dest->Goto(left_value < right_value);
+          break;
+        case equal:
+          dest->Goto(left_value == right_value);
+          break;
+        case greater_equal:
+          dest->Goto(left_value >= right_value);
+          break;
+        default:
+          UNREACHABLE();
+      }
+    } else {
+      // Only one side is a constant 1 character string.
+      // If left side is a constant 1-character string, reverse the operands.
+      // Since one side is a constant string, conversion order does not matter.
+      if (left_side_constant_1_char_string) {
+        Result temp = left_side;
+        left_side = right_side;
+        right_side = temp;
+        cc = ReverseCondition(cc);
+        // This may reintroduce greater or less_equal as the value of cc.
+        // CompareStub and the inline code both support all values of cc.
+      }
+      // Implement comparison against a constant string, inlining the case
+      // where both sides are strings.
+      left_side.ToRegister();
+
+      // Here we split control flow to the stub call and inlined cases
+      // before finally splitting it to the control destination.  We use
+      // a jump target and branching to duplicate the virtual frame at
+      // the first split.  We manually handle the off-frame references
+      // by reconstituting them on the non-fall-through path.
+      JumpTarget is_not_string, is_string;
+      Register left_reg = left_side.reg();
+      Handle<Object> right_val = right_side.handle();
+      __ test(left_side.reg(), Immediate(kSmiTagMask));
+      is_not_string.Branch(zero, &left_side);
+      Result temp = allocator_->Allocate();
+      ASSERT(temp.is_valid());
+      __ mov(temp.reg(),
+             FieldOperand(left_side.reg(), HeapObject::kMapOffset));
+      __ movzx_b(temp.reg(),
+                 FieldOperand(temp.reg(), Map::kInstanceTypeOffset));
+      // If we are testing for equality then make use of the symbol shortcut.
+      // Check if the right left hand side has the same type as the left hand
+      // side (which is always a symbol).
+      if (cc == equal) {
+        Label not_a_symbol;
+        ASSERT(kSymbolTag != 0);
+        // Ensure that no non-strings have the symbol bit set.
+        ASSERT(kNotStringTag + kIsSymbolMask > LAST_TYPE);
+        __ test(temp.reg(), Immediate(kIsSymbolMask));  // Test the symbol bit.
+        __ j(zero, &not_a_symbol);
+        // They are symbols, so do identity compare.
+        __ cmp(left_side.reg(), right_side.handle());
+        dest->true_target()->Branch(equal);
+        dest->false_target()->Branch(not_equal);
+        __ bind(&not_a_symbol);
+      }
+      // If the receiver is not a string of the type we handle call the stub.
+      __ and_(temp.reg(),
+          kIsNotStringMask | kStringRepresentationMask | kStringEncodingMask);
+      __ cmp(temp.reg(), kStringTag | kSeqStringTag | kAsciiStringTag);
+      temp.Unuse();
+      is_string.Branch(equal, &left_side);
+
+      // Setup and call the compare stub.
+      is_not_string.Bind(&left_side);
+      CompareStub stub(cc, strict, kCantBothBeNaN);
+      Result result = frame_->CallStub(&stub, &left_side, &right_side);
+      result.ToRegister();
+      __ cmp(result.reg(), 0);
+      result.Unuse();
+      dest->true_target()->Branch(cc);
+      dest->false_target()->Jump();
+
+      is_string.Bind(&left_side);
+      // Here we know we have a sequential ASCII string.
+      left_side = Result(left_reg);
+      right_side = Result(right_val);
+      Result temp2 = allocator_->Allocate();
+      ASSERT(temp2.is_valid());
+      // Test string equality and comparison.
+      if (cc == equal) {
+        Label comparison_done;
+        __ cmp(FieldOperand(left_side.reg(), String::kLengthOffset),
+               Immediate(1));
+        __ j(not_equal, &comparison_done);
+        __ cmpb(FieldOperand(left_side.reg(), SeqAsciiString::kHeaderSize),
+                String::cast(*right_side.handle())->Get(0));
+        __ bind(&comparison_done);
+      } else {
+        __ mov(temp2.reg(),
+               FieldOperand(left_side.reg(), String::kLengthOffset));
+        __ sub(Operand(temp2.reg()), Immediate(1));
+        Label comparison;
+        // If the length is 0 then our subtraction gave -1 which compares less
+        // than any character.
+        __ j(negative, &comparison);
+        // Otherwise load the first character.
+        __ movzx_b(temp2.reg(),
+                   FieldOperand(left_side.reg(), SeqAsciiString::kHeaderSize));
+        __ bind(&comparison);
+        // Compare the first character of the string with out constant
+        // 1-character string.
+        __ cmp(Operand(temp2.reg()),
+               Immediate(String::cast(*right_side.handle())->Get(0)));
+        Label characters_were_different;
+        __ j(not_equal, &characters_were_different);
+        // If the first character is the same then the long string sorts after
+        // the short one.
+        __ cmp(FieldOperand(left_side.reg(), String::kLengthOffset),
+               Immediate(1));
+        __ bind(&characters_were_different);
+      }
+      temp2.Unuse();
+      left_side.Unuse();
+      right_side.Unuse();
+      dest->Split(cc);
+    }
   } else {
     // Neither side is a constant Smi or null.
     // If either side is a non-smi constant, skip the smi check.
     bool known_non_smi =
         (left_side.is_constant() && !left_side.handle()->IsSmi()) ||
         (right_side.is_constant() && !right_side.handle()->IsSmi());
+    NaNInformation nan_info =
+        (CouldBeNaN(left_side) && CouldBeNaN(right_side)) ?
+        kBothCouldBeNaN :
+        kCantBothBeNaN;
     left_side.ToRegister();
     right_side.ToRegister();
 
     if (known_non_smi) {
       // When non-smi, call out to the compare stub.
-      CompareStub stub(cc, strict);
+      CompareStub stub(cc, strict, nan_info);
       Result answer = frame_->CallStub(&stub, &left_side, &right_side);
       if (cc == equal) {
         __ test(answer.reg(), Operand(answer.reg()));
@@ -2113,7 +2265,7 @@ void CodeGenerator::Comparison(AstNode* node,
       temp.Unuse();
       is_smi.Branch(zero, taken);
       // When non-smi, call out to the compare stub.
-      CompareStub stub(cc, strict);
+      CompareStub stub(cc, strict, nan_info);
       Result answer = frame_->CallStub(&stub, &left_side, &right_side);
       if (cc == equal) {
         __ test(answer.reg(), Operand(answer.reg()));
@@ -8229,6 +8381,10 @@ void CompareStub::Generate(MacroAssembler* masm) {
       // Test for NaN. Sadly, we can't just compare to Factory::nan_value(),
       // so we do the second best thing - test it ourselves.
 
+      if (never_nan_nan_) {
+        __ Set(eax, Immediate(0));
+        __ ret(0);
+      } else {
         Label return_equal;
         Label heap_number;
         // If it's not a heap number, then return equal.
@@ -8240,8 +8396,8 @@ void CompareStub::Generate(MacroAssembler* masm) {
         __ ret(0);
 
         __ bind(&heap_number);
-      // It is a heap number, so return non-equal if it's NaN and equal if it's
-      // not NaN.
+        // It is a heap number, so return non-equal if it's NaN and equal if
+        // it's not NaN.
         // The representation of NaN values has all exponent bits (52..62) set,
         // and not all mantissa bits (0..51) clear.
         // We only accept QNaNs, which have bit 51 set.
@@ -8253,11 +8409,13 @@ void CompareStub::Generate(MacroAssembler* masm) {
         ASSERT_NE(0, (kQuietNaNHighBitsMask << 1) & 0x80000000u);
         __ mov(edx, FieldOperand(edx, HeapNumber::kExponentOffset));
         __ xor_(eax, Operand(eax));
-      // Shift value and mask so kQuietNaNHighBitsMask applies to topmost bits.
+        // Shift value and mask so kQuietNaNHighBitsMask applies to topmost
+        // bits.
         __ add(edx, Operand(edx));
         __ cmp(edx, kQuietNaNHighBitsMask << 1);
         __ setcc(above_equal, eax);
         __ ret(0);
+      }
 
       __ bind(&not_identical);
     }
@@ -8982,10 +9140,55 @@ void InstanceofStub::Generate(MacroAssembler* masm) {
 }
 
 
+// Unfortunately you have to run without snapshots to see most of these
+// names in the profile since most compare stubs end up in the snapshot.
+const char* CompareStub::GetName() {
+  switch (cc_) {
+    case less: return "CompareStub_LT";
+    case greater: return "CompareStub_GT";
+    case less_equal: return "CompareStub_LE";
+    case greater_equal: return "CompareStub_GE";
+    case not_equal: {
+      if (strict_) {
+        if (never_nan_nan_) {
+          return "CompareStub_NE_STRICT_NO_NAN";
+        } else {
+          return "CompareStub_NE_STRICT";
+        }
+      } else {
+        if (never_nan_nan_) {
+          return "CompareStub_NE_NO_NAN";
+        } else {
+          return "CompareStub_NE";
+        }
+      }
+    }
+    case equal: {
+      if (strict_) {
+        if (never_nan_nan_) {
+          return "CompareStub_EQ_STRICT_NO_NAN";
+        } else {
+          return "CompareStub_EQ_STRICT";
+        }
+      } else {
+        if (never_nan_nan_) {
+          return "CompareStub_EQ_NO_NAN";
+        } else {
+          return "CompareStub_EQ";
+        }
+      }
+    }
+    default: return "CompareStub";
+  }
+}
+
+
 int CompareStub::MinorKey() {
-  // Encode the two parameters in a unique 16 bit value.
-  ASSERT(static_cast<unsigned>(cc_) < (1 << 15));
-  return (static_cast<unsigned>(cc_) << 1) | (strict_ ? 1 : 0);
+  // Encode the three parameters in a unique 16 bit value.
+  ASSERT(static_cast<unsigned>(cc_) < (1 << 14));
+  int nnn_value = (never_nan_nan_ ? 2 : 0);
+  if (cc_ != equal) nnn_value = 0;  // Avoid duplicate stubs.
+  return (static_cast<unsigned>(cc_) << 2) | nnn_value | (strict_ ? 1 : 0);
 }
 
 

src/ia32/ic-ia32.cc

@@ -313,6 +313,7 @@ void KeyedLoadIC::GenerateGeneric(MacroAssembler* masm) {
 
   // Is the string a symbol?
   __ movzx_b(ebx, FieldOperand(edx, Map::kInstanceTypeOffset));
+  ASSERT(kSymbolTag != 0);
   __ test(ebx, Immediate(kIsSymbolMask));
   __ j(zero, &slow, not_taken);
 

src/ia32/virtual-frame-ia32.h

@@ -395,6 +395,8 @@ class VirtualFrame: public ZoneObject {
   // Pushing a result invalidates it (its contents become owned by the
   // frame).
   void Push(Result* result) {
+    // This assert will trigger if you try to push the same value twice.
+    ASSERT(result->is_valid());
     if (result->is_register()) {
       Push(result->reg());
     } else {

src/objects-inl.h

@@ -150,8 +150,12 @@ bool Object::IsString() {
 bool Object::IsSymbol() {
   if (!this->IsHeapObject()) return false;
   uint32_t type = HeapObject::cast(this)->map()->instance_type();
-  return (type & (kIsNotStringMask | kIsSymbolMask)) ==
-         (kStringTag | kSymbolTag);
+  // Because the symbol tag is non-zero and no non-string types have the
+  // symbol bit set we can test for symbols with a very simple test
+  // operation.
+  ASSERT(kSymbolTag != 0);
+  ASSERT(kNotStringTag + kIsSymbolMask > LAST_TYPE);
+  return (type & kIsSymbolMask) != 0;
 }
 
 
@@ -226,7 +230,8 @@ StringShape::StringShape(InstanceType t)
 
 bool StringShape::IsSymbol() {
   ASSERT(valid());
-  return (type_ & kIsSymbolMask) == kSymbolTag;
+  ASSERT(kSymbolTag != 0);
+  return (type_ & kIsSymbolMask) != 0;
 }
 
 

src/objects.h

@@ -383,11 +383,12 @@ const uint32_t kIsNotStringMask = 0x80;
 const uint32_t kStringTag = 0x0;
 const uint32_t kNotStringTag = 0x80;
 
-// If bit 7 is clear, bit 5 indicates that the string is a symbol (if set) or
-// not (if cleared).
-const uint32_t kIsSymbolMask = 0x20;
+// Bit 6 indicates that the object is a symbol (if set) or not (if cleared).
+// There are not enough types that the non-string types (with bit 7 set) can
+// have bit 6 set too.
+const uint32_t kIsSymbolMask = 0x40;
 const uint32_t kNotSymbolTag = 0x0;
-const uint32_t kSymbolTag = 0x20;
+const uint32_t kSymbolTag = 0x40;
 
 // If bit 7 is clear then bit 2 indicates whether the string consists of
 // two-byte characters or one-byte characters.

src/x64/codegen-x64.cc

@@ -6264,6 +6264,10 @@ void CompareStub::Generate(MacroAssembler* masm) {
       // Test for NaN. Sadly, we can't just compare to Factory::nan_value(),
       // so we do the second best thing - test it ourselves.
 
+      if (never_nan_nan_) {
+        __ xor_(rax, rax);
+        __ ret(0);
+      } else {
         Label return_equal;
         Label heap_number;
         // If it's not a heap number, then return equal.
@@ -6275,8 +6279,8 @@ void CompareStub::Generate(MacroAssembler* masm) {
         __ ret(0);
 
         __ bind(&heap_number);
-      // It is a heap number, so return non-equal if it's NaN and equal if it's
-      // not NaN.
+        // It is a heap number, so return non-equal if it's NaN and equal if
+        // it's not NaN.
         // The representation of NaN values has all exponent bits (52..62) set,
         // and not all mantissa bits (0..51) clear.
         // We only allow QNaNs, which have bit 51 set (which also rules out
@@ -6292,6 +6296,7 @@ void CompareStub::Generate(MacroAssembler* masm) {
         __ cmpl(rdx, Immediate(kQuietNaNHighBitsMask << 1));
         __ setcc(above_equal, rax);
         __ ret(0);
+      }
 
       __ bind(&not_identical);
     }
@@ -6438,9 +6443,11 @@ void CompareStub::BranchIfNonSymbol(MacroAssembler* masm,
   __ movq(scratch, FieldOperand(object, HeapObject::kMapOffset));
   __ movzxbq(scratch,
              FieldOperand(scratch, Map::kInstanceTypeOffset));
-  __ and_(scratch, Immediate(kIsSymbolMask | kIsNotStringMask));
-  __ cmpb(scratch, Immediate(kSymbolTag | kStringTag));
-  __ j(not_equal, label);
+  // Ensure that no non-strings have the symbol bit set.
+  ASSERT(kNotStringTag + kIsSymbolMask > LAST_TYPE);
+  ASSERT(kSymbolTag != 0);
+  __ testb(scratch, Immediate(kIsSymbolMask));
+  __ j(zero, label);
 }
 
 
@@ -7740,9 +7747,52 @@ void GenericBinaryOpStub::GenerateReturn(MacroAssembler* masm) {
 
 
 int CompareStub::MinorKey() {
-  // Encode the two parameters in a unique 16 bit value.
-  ASSERT(static_cast<unsigned>(cc_) < (1 << 15));
-  return (static_cast<unsigned>(cc_) << 1) | (strict_ ? 1 : 0);
+  // Encode the three parameters in a unique 16 bit value.
+  ASSERT(static_cast<unsigned>(cc_) < (1 << 14));
+  int nnn_value = (never_nan_nan_ ? 2 : 0);
+  if (cc_ != equal) nnn_value = 0;  // Avoid duplicate stubs.
+  return (static_cast<unsigned>(cc_) << 2) | nnn_value | (strict_ ? 1 : 0);
+}
+
+
+const char* CompareStub::GetName() {
+  switch(cc_) {
+    case less: return "CompareStub_LT";
+    case greater: return "CompareStub_GT";
+    case less_equal: return "CompareStub_LE";
+    case greater_equal: return "CompareStub_GE";
+    case not_equal: {
+      if (strict_) {
+        if (never_nan_nan_) {
+          return "CompareStub_NE_STRICT_NO_NAN";
+        } else {
+          return "CompareStub_NE_STRICT";
+        }
+      } else {
+        if (never_nan_nan_) {
+          return "CompareStub_NE_NO_NAN";
+        } else {
+          return "CompareStub_NE";
+        }
+      }
+    }
+    case equal: {
+      if (strict_) {
+        if (never_nan_nan_) {
+          return "CompareStub_EQ_STRICT_NO_NAN";
+        } else {
+          return "CompareStub_EQ_STRICT";
+        }
+      } else {
+        if (never_nan_nan_) {
+          return "CompareStub_EQ_NO_NAN";
+        } else {
+          return "CompareStub_EQ";
+        }
+      }
+    }
+    default: return "CompareStub";
+  }
 }
 
 

src/x64/ic-x64.cc

@@ -330,6 +330,7 @@ void KeyedLoadIC::GenerateGeneric(MacroAssembler* masm) {
 
   // Is the string a symbol?
   __ j(not_zero, &index_string);  // The value in rbx is used at jump target.
+  ASSERT(kSymbolTag != 0);
   __ testb(FieldOperand(rdx, Map::kInstanceTypeOffset),
            Immediate(kIsSymbolMask));
   __ j(zero, &slow);

test/mjsunit/bit-not.js

@@ -25,43 +25,43 @@
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-function testBitNot(x) {
+function testBitNot(x, name) {
   // The VM constant folds so we use that to check the result.
   var expected = eval("~(" + x + ")");
   var actual = ~x;
-  assertEquals(expected, actual, "x: " + x);
+  assertEquals(expected, actual, "x: " + name);
 
   // Test the path where we can overwrite the result. Use -
   // to avoid concatenating strings.
   expected = eval("~(" + x + " - 0.01)");
   actual = ~(x - 0.01);
-  assertEquals(expected, actual, "x - 0.01: " + x);
+  assertEquals(expected, actual, "x - 0.01: " + name);
 }
 
 
-testBitNot(0);
-testBitNot(1);
-testBitNot(-1);
-testBitNot(100);
-testBitNot(0x40000000);
-testBitNot(0x7fffffff);
-testBitNot(0x80000000);
+testBitNot(0, 0);
+testBitNot(1, 1);
+testBitNot(-1, 1);
+testBitNot(100, 100);
+testBitNot(0x40000000, "0x40000000");
+testBitNot(0x7fffffff, "0x7fffffff");
+testBitNot(0x80000000, "0x80000000");
 
-testBitNot(2.2);
-testBitNot(-2.3);
-testBitNot(Infinity);
-testBitNot(NaN);
-testBitNot(-Infinity);
-testBitNot(0x40000000 + 0.12345);
-testBitNot(0x40000000 - 0.12345);
-testBitNot(0x7fffffff + 0.12345);
-testBitNot(0x7fffffff - 0.12345);
-testBitNot(0x80000000 + 0.12345);
-testBitNot(0x80000000 - 0.12345);
+testBitNot(2.2, 2.2);
+testBitNot(-2.3, -2.3);
+testBitNot(Infinity, "Infinity");
+testBitNot(NaN, "NaN");
+testBitNot(-Infinity, "-Infinity");
+testBitNot(0x40000000 + 0.12345, "float1");
+testBitNot(0x40000000 - 0.12345, "float2");
+testBitNot(0x7fffffff + 0.12345, "float3");
+testBitNot(0x7fffffff - 0.12345, "float4");
+testBitNot(0x80000000 + 0.12345, "float5");
+testBitNot(0x80000000 - 0.12345, "float6");
 
-testBitNot("0");
-testBitNot("2.3");
-testBitNot("-9.4");
+testBitNot("0", "string0");
+testBitNot("2.3", "string2.3");
+testBitNot("-9.4", "string-9.4");
 
 
 // Try to test that we can deal with allocation failures in

test/mjsunit/compare-character.js

+// Copyright 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.
+
+// Test the optimized implementation of comparison with single-character
+// strings.
+
+var a = ['', String.fromCharCode(0), ' ', 'e', 'erik', 'f', 'foo', 'g', 'goo',
+         -1, 0, 1, 1.2, -7.9, true, false, 'foo', '0', 'NaN' ];
+for (var i in a) {
+  var x = a[i];
+  var f = 'f';
+
+  assertEquals(x == f, x == 'f', "==" + x);
+  assertEquals(x === f, x === 'f', "===" + x);
+  assertEquals(x < f, x < 'f', "<" + x);
+  assertEquals(x <= f, x <= 'f', "<=" + x);
+  assertEquals(x > f, x > 'f', ">" + x);
+  assertEquals(x >= f, x >= 'f', ">=" + x);
+  assertEquals(f == x, 'f' == x, "==r" + x);
+  assertEquals(f === x, 'f' === x, "===r" + x);
+  assertEquals(f > x, 'f' > x, "<r" + x);
+  assertEquals(f >= x, 'f' >= x, "<=r" + x);
+  assertEquals(f < x, 'f' < x, ">r" + x);
+  assertEquals(f <= x, 'f' <= x, ">=r" + x);
+}
+

test/mjsunit/compare-nan.js

@@ -42,3 +42,25 @@ for (var i in a) {
   assertFalse(x <= NaN, "" + x + " <= NaN");
   assertFalse(x >= NaN, "" + x + " >= NaN");
 }
+
+var b = ["NaN", "-1", "0", "1", "1.2", "-7.9", "true", "false", "'foo'", "'0'",
+         "'NaN'" ];
+for (var i in b) {
+  var x = b[i];
+  var program =
+      "assertFalse(NaN == " + x + ", 'NaN == ' + " + x + ");\n" +
+      "assertFalse(NaN === " + x + ", 'NaN === ' + " + x + ");\n" +
+      "assertFalse(NaN < " + x + ", 'NaN < ' + " + x + ");\n" +
+      "assertFalse(NaN > " + x + ", 'NaN > ' + " + x + ");\n" +
+      "assertFalse(NaN <= " + x + ", 'NaN <= ' + " + x + ");\n" +
+      "assertFalse(NaN >= " + x + ", 'NaN >= ' + " + x + ");\n" +
+
+      "assertFalse(" + x + " == NaN, '' + " + x + " + ' == NaN');\n" +
+      "assertFalse(" + x + " === NaN, '' + " + x + " + ' === NaN');\n" +
+      "assertFalse(" + x + " < NaN, '' + " + x + " + ' < NaN');\n" +
+      "assertFalse(" + x + " > NaN, '' + " + x + " + ' > NaN');\n" +
+      "assertFalse(" + x + " <= NaN, '' + " + x + " + ' <= NaN');\n" +
+      "assertFalse(" + x + " >= NaN, '' + " + x + " + ' >= NaN');\n";
+  eval(program);
+}
+