Fix error introduced in version 3820. Add optimization suggested by the error.

Review URL: http://codereview.chromium.org/597006

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@3823 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/arm/stub-cache-arm.cc

@@ -189,8 +189,9 @@ void StubCompiler::GenerateLoadArrayLength(MacroAssembler* masm,
 }
 
 
-// Generate code to check if an object is a string.  If the object is
-// a string, the map's instance type is left in the scratch1 register.
+// Generate code to check if an object is a string.  If the object is a
+// heap object, its map's instance type is left in the scratch1 register.
+// If this is not needed, scratch1 and scratch2 may be the same register.
 static void GenerateStringCheck(MacroAssembler* masm,
                                 Register receiver,
                                 Register scratch1,
@@ -220,13 +221,11 @@ void StubCompiler::GenerateLoadStringLength(MacroAssembler* masm,
                                             Register scratch1,
                                             Register scratch2,
                                             Label* miss) {
-  Label check_string, check_wrapper;
+  Label check_wrapper;
 
-  __ bind(&check_string);
   // Check if the object is a string leaving the instance type in the
   // scratch1 register.
-  GenerateStringCheck(masm, receiver, scratch1, scratch2,
-                      miss, &check_wrapper);
+  GenerateStringCheck(masm, receiver, scratch1, scratch2, miss, &check_wrapper);
 
   // Load length directly from the string.
   __ ldr(r0, FieldMemOperand(receiver, String::kLengthOffset));
@@ -238,9 +237,12 @@ void StubCompiler::GenerateLoadStringLength(MacroAssembler* masm,
   __ cmp(scratch1, Operand(JS_VALUE_TYPE));
   __ b(ne, miss);
 
-  // Unwrap the value in place and check if the wrapped value is a string.
-  __ ldr(receiver, FieldMemOperand(receiver, JSValue::kValueOffset));
-  __ b(&check_string);
+  // Unwrap the value and check if the wrapped value is a string.
+  __ ldr(scratch1, FieldMemOperand(receiver, JSValue::kValueOffset));
+  GenerateStringCheck(masm, scratch1, scratch2, scratch2, miss, miss);
+  __ ldr(r0, FieldMemOperand(scratch1, String::kLengthOffset));
+  __ mov(r0, Operand(r0, LSL, kSmiTagSize));
+  __ Ret();
 }
 
 

src/ia32/stub-cache-ia32.cc

@@ -229,14 +229,13 @@ void StubCompiler::GenerateLoadStringLength(MacroAssembler* masm,
                                             Register scratch1,
                                             Register scratch2,
                                             Label* miss) {
-  Label load_length, check_wrapper;
+  Label check_wrapper;
 
   // Check if the object is a string leaving the instance type in the
   // scratch register.
   GenerateStringCheck(masm, receiver, scratch1, miss, &check_wrapper);
 
   // Load length from the string and convert to a smi.
-  __ bind(&load_length);
   __ mov(eax, FieldOperand(receiver, String::kLengthOffset));
   __ SmiTag(eax);
   __ ret(0);
@@ -250,7 +249,9 @@ void StubCompiler::GenerateLoadStringLength(MacroAssembler* masm,
   // directly if it is.
   __ mov(scratch2, FieldOperand(receiver, JSValue::kValueOffset));
   GenerateStringCheck(masm, scratch2, scratch1, miss, miss);
-  __ jmp(&load_length);
+  __ mov(eax, FieldOperand(scratch2, String::kLengthOffset));
+  __ SmiTag(eax);
+  __ ret(0);
 }
 
 

src/stub-cache.h

@@ -346,6 +346,7 @@ class StubCompiler BASE_EMBEDDED {
   static void GenerateLoadGlobalFunctionPrototype(MacroAssembler* masm,
                                                   int index,
                                                   Register prototype);
+
   static void GenerateFastPropertyLoad(MacroAssembler* masm,
                                        Register dst, Register src,
                                        JSObject* holder, int index);
@@ -354,16 +355,19 @@ class StubCompiler BASE_EMBEDDED {
                                       Register receiver,
                                       Register scratch,
                                       Label* miss_label);
+
   static void GenerateLoadStringLength(MacroAssembler* masm,
-                                        Register receiver,
-                                        Register scratch1,
-                                        Register scratch2,
-                                        Label* miss_label);
+                                       Register receiver,
+                                       Register scratch1,
+                                       Register scratch2,
+                                       Label* miss_label);
+
   static void GenerateLoadFunctionPrototype(MacroAssembler* masm,
                                             Register receiver,
                                             Register scratch1,
                                             Register scratch2,
                                             Label* miss_label);
+
   static void GenerateStoreField(MacroAssembler* masm,
                                  Builtins::Name storage_extend,
                                  JSObject* object,
@@ -373,6 +377,7 @@ class StubCompiler BASE_EMBEDDED {
                                  Register name_reg,
                                  Register scratch,
                                  Label* miss_label);
+
   static void GenerateLoadMiss(MacroAssembler* masm, Code::Kind kind);
 
   // Check the integrity of the prototype chain to make sure that the

src/x64/stub-cache-x64.cc

@@ -317,14 +317,13 @@ void StubCompiler::GenerateLoadStringLength(MacroAssembler* masm,
                                             Register scratch1,
                                             Register scratch2,
                                             Label* miss) {
-  Label load_length, check_wrapper;
+  Label check_wrapper;
 
   // Check if the object is a string leaving the instance type in the
   // scratch register.
   GenerateStringCheck(masm, receiver, scratch1, miss, &check_wrapper);
 
   // Load length directly from the string.
-  __ bind(&load_length);
   __ movl(rax, FieldOperand(receiver, String::kLengthOffset));
   __ Integer32ToSmi(rax, rax);
   __ ret(0);
@@ -338,8 +337,9 @@ void StubCompiler::GenerateLoadStringLength(MacroAssembler* masm,
   // directly if it is.
   __ movq(scratch2, FieldOperand(receiver, JSValue::kValueOffset));
   GenerateStringCheck(masm, scratch2, scratch1, miss, miss);
-  __ movq(receiver, scratch2);
-  __ jmp(&load_length);
+  __ movl(rax, FieldOperand(scratch2, String::kLengthOffset));
+  __ Integer32ToSmi(rax, rax);
+  __ ret(0);
 }