Cleanup StringAddFlags.

src/x64/code-stubs-x64.cc

Index: src/x64/code-stubs-x64.cc
diff --git a/src/x64/code-stubs-x64.cc b/src/x64/code-stubs-x64.cc
index 0b74ace6f8b50b264021c7718fa726402bbb6017..801d8f309b7182487ebb4c6d1eea51ede4ece83b 100644
--- a/src/x64/code-stubs-x64.cc
+++ b/src/x64/code-stubs-x64.cc
@@ -998,8 +998,8 @@ void BinaryOpStub::GenerateAddStrings(MacroAssembler* masm) {
   __ JumpIfSmi(left, &left_not_string, Label::kNear);
   __ CmpObjectType(left, FIRST_NONSTRING_TYPE, rcx);
   __ j(above_equal, &left_not_string, Label::kNear);
-  StringAddStub string_add_left_stub((StringAddFlags)
-      (ERECT_FRAME | NO_STRING_CHECK_LEFT_IN_STUB));
+  StringAddStub string_add_left_stub(
+      (StringAddFlags)(STRING_ADD_CHECK_RIGHT | STRING_ADD_ERECT_FRAME));
   BinaryOpStub_GenerateRegisterArgsPushUnderReturn(masm);
   __ TailCallStub(&string_add_left_stub);
 
@@ -1009,8 +1009,8 @@ void BinaryOpStub::GenerateAddStrings(MacroAssembler* masm) {
   __ CmpObjectType(right, FIRST_NONSTRING_TYPE, rcx);
   __ j(above_equal, &call_runtime, Label::kNear);
 
-  StringAddStub string_add_right_stub((StringAddFlags)
-      (ERECT_FRAME | NO_STRING_CHECK_RIGHT_IN_STUB));
+  StringAddStub string_add_right_stub(
+      (StringAddFlags)(STRING_ADD_CHECK_LEFT | STRING_ADD_ERECT_FRAME));
   BinaryOpStub_GenerateRegisterArgsPushUnderReturn(masm);
   __ TailCallStub(&string_add_right_stub);
 
@@ -1085,8 +1085,8 @@ void BinaryOpStub::GenerateBothStringStub(MacroAssembler* masm) {
   __ CmpObjectType(right, FIRST_NONSTRING_TYPE, rcx);
   __ j(above_equal, &call_runtime);
 
-  StringAddStub string_add_stub((StringAddFlags)
-                                (ERECT_FRAME | NO_STRING_CHECK_IN_STUB));
+  StringAddStub string_add_stub(
+      (StringAddFlags)(STRING_ADD_CHECK_NONE | STRING_ADD_ERECT_FRAME));
   BinaryOpStub_GenerateRegisterArgsPushUnderReturn(masm);
   __ TailCallStub(&string_add_stub);
 
@@ -4494,7 +4494,9 @@ void StringAddStub::Generate(MacroAssembler* masm) {
   __ movq(rdx, Operand(rsp, 1 * kPointerSize));  // Second argument (right).
 
   // Make sure that both arguments are strings if not known in advance.
-  if ((flags_ & NO_STRING_ADD_FLAGS) != 0) {
+  // Otherwise, at least one of the arguments is definitely a string,
+  // and we convert the one that is not known to be a string.
+  if ((flags_ & STRING_ADD_CHECK_BOTH) == STRING_ADD_CHECK_BOTH) {
     __ JumpIfSmi(rax, &call_runtime);
     __ CmpObjectType(rax, FIRST_NONSTRING_TYPE, r8);
     __ j(above_equal, &call_runtime);
@@ -4503,20 +4505,16 @@ void StringAddStub::Generate(MacroAssembler* masm) {
     __ JumpIfSmi(rdx, &call_runtime);
     __ CmpObjectType(rdx, FIRST_NONSTRING_TYPE, r9);
     __ j(above_equal, &call_runtime);
-  } else {
-    // Here at least one of the arguments is definitely a string.
-    // We convert the one that is not known to be a string.
-    if ((flags_ & NO_STRING_CHECK_LEFT_IN_STUB) == 0) {
-      ASSERT((flags_ & NO_STRING_CHECK_RIGHT_IN_STUB) != 0);
-      GenerateConvertArgument(masm, 2 * kPointerSize, rax, rbx, rcx, rdi,
-                              &call_builtin);
-      builtin_id = Builtins::STRING_ADD_RIGHT;
-    } else if ((flags_ & NO_STRING_CHECK_RIGHT_IN_STUB) == 0) {
-      ASSERT((flags_ & NO_STRING_CHECK_LEFT_IN_STUB) != 0);
-      GenerateConvertArgument(masm, 1 * kPointerSize, rdx, rbx, rcx, rdi,
-                              &call_builtin);
-      builtin_id = Builtins::STRING_ADD_LEFT;
-    }
+  } else if ((flags_ & STRING_ADD_CHECK_LEFT) == STRING_ADD_CHECK_LEFT) {
+    ASSERT((flags_ & STRING_ADD_CHECK_RIGHT) == 0);
+    GenerateConvertArgument(masm, 2 * kPointerSize, rax, rbx, rcx, rdi,
+                            &call_builtin);
+    builtin_id = Builtins::STRING_ADD_RIGHT;
+  } else if ((flags_ & STRING_ADD_CHECK_RIGHT) == STRING_ADD_CHECK_RIGHT) {
+    ASSERT((flags_ & STRING_ADD_CHECK_LEFT) == 0);
+    GenerateConvertArgument(masm, 1 * kPointerSize, rdx, rbx, rcx, rdi,
+                            &call_builtin);
+    builtin_id = Builtins::STRING_ADD_LEFT;
   }
 
   // Both arguments are strings.
@@ -4552,7 +4550,7 @@ void StringAddStub::Generate(MacroAssembler* masm) {
 
   // If arguments where known to be strings, maps are not loaded to r8 and r9
   // by the code above.
-  if (flags_ != NO_STRING_ADD_FLAGS) {
+  if ((flags_ & STRING_ADD_CHECK_BOTH) != STRING_ADD_CHECK_BOTH) {
     __ movq(r8, FieldOperand(rax, HeapObject::kMapOffset));
     __ movq(r9, FieldOperand(rdx, HeapObject::kMapOffset));
   }
@@ -4772,7 +4770,7 @@ void StringAddStub::Generate(MacroAssembler* masm) {
   // Just jump to runtime to add the two strings.
   __ bind(&call_runtime);
 
-  if ((flags_ & ERECT_FRAME) != 0) {
+  if ((flags_ & STRING_ADD_ERECT_FRAME) != 0) {
     GenerateRegisterArgsPop(masm, rcx);
     // Build a frame
     {
@@ -4787,7 +4785,7 @@ void StringAddStub::Generate(MacroAssembler* masm) {
 
   if (call_builtin.is_linked()) {
     __ bind(&call_builtin);
-    if ((flags_ & ERECT_FRAME) != 0) {
+    if ((flags_ & STRING_ADD_ERECT_FRAME) != 0) {
       GenerateRegisterArgsPop(masm, rcx);
       // Build a frame
       {