[builtins] Simplify String constructor code.

src/x64/builtins-x64.cc

Index: src/x64/builtins-x64.cc
diff --git a/src/x64/builtins-x64.cc b/src/x64/builtins-x64.cc
index 685701ef740161dd4fa32f653c55c9f6a40438b4..a244c98558732f9a1b762332886e828050c1bfbb 100644
--- a/src/x64/builtins-x64.cc
+++ b/src/x64/builtins-x64.cc
@@ -1312,121 +1312,75 @@ void Builtins::Generate_StringConstructCode(MacroAssembler* masm) {
   //  -- rsp[(argc - n) * 8] : arg[n] (zero-based)
   //  -- rsp[(argc + 1) * 8] : receiver
   // -----------------------------------
-  Counters* counters = masm->isolate()->counters();
-  __ IncrementCounter(counters->string_ctor_calls(), 1);
-
-  if (FLAG_debug_code) {
-    __ LoadGlobalFunction(Context::STRING_FUNCTION_INDEX, rcx);
-    __ cmpp(rdi, rcx);
-    __ Assert(equal, kUnexpectedStringFunction);
-  }
-
-  // Load the first argument into rax and get rid of the rest
-  // (including the receiver).
-  StackArgumentsAccessor args(rsp, rax);
-  Label no_arguments;
-  __ testp(rax, rax);
-  __ j(zero, &no_arguments);
-  __ movp(rbx, args.GetArgumentOperand(1));
-  __ PopReturnAddressTo(rcx);
-  __ leap(rsp, Operand(rsp, rax, times_pointer_size, kPointerSize));
-  __ PushReturnAddressFrom(rcx);
-  __ movp(rax, rbx);
-
-  // Lookup the argument in the number to string cache.
-  Label not_cached, argument_is_string;
-  __ LookupNumberStringCache(rax,  // Input.
-                             rbx,  // Result.
-                             rcx,  // Scratch 1.
-                             rdx,  // Scratch 2.
-                             &not_cached);
-  __ IncrementCounter(counters->string_ctor_cached_number(), 1);
-  __ bind(&argument_is_string);
-
-  // ----------- S t a t e -------------
-  //  -- rbx    : argument converted to string
-  //  -- rdi    : constructor function
-  //  -- rsp[0] : return address
-  // -----------------------------------
 
-  // Allocate a JSValue and put the tagged pointer into rax.
-  Label gc_required;
-  __ Allocate(JSValue::kSize,
-              rax,  // Result.
-              rcx,  // New allocation top (we ignore it).
-              no_reg,
-              &gc_required,
-              TAG_OBJECT);
-
-  // Set the map.
-  __ LoadGlobalFunctionInitialMap(rdi, rcx);
-  if (FLAG_debug_code) {
-    __ cmpb(FieldOperand(rcx, Map::kInstanceSizeOffset),
-            Immediate(JSValue::kSize >> kPointerSizeLog2));
-    __ Assert(equal, kUnexpectedStringWrapperInstanceSize);
-    __ cmpb(FieldOperand(rcx, Map::kUnusedPropertyFieldsOffset), Immediate(0));
-    __ Assert(equal, kUnexpectedUnusedPropertiesOfStringWrapper);
+  // 1. Load the first argument into rbx and get rid of the rest (including the
+  // receiver).
+  {
+    StackArgumentsAccessor args(rsp, rax);
+    Label no_arguments, done;
+    __ testp(rax, rax);
+    __ j(zero, &no_arguments, Label::kNear);
+    __ movp(rbx, args.GetArgumentOperand(1));
+    __ jmp(&done, Label::kNear);
+    __ bind(&no_arguments);
+    __ LoadRoot(rbx, Heap::kempty_stringRootIndex);
+    __ bind(&done);
+    __ PopReturnAddressTo(rcx);
+    __ leap(rsp, Operand(rsp, rax, times_pointer_size, kPointerSize));
+    __ PushReturnAddressFrom(rcx);
   }
-  __ movp(FieldOperand(rax, HeapObject::kMapOffset), rcx);
-
-  // Set properties and elements.
-  __ LoadRoot(rcx, Heap::kEmptyFixedArrayRootIndex);
-  __ movp(FieldOperand(rax, JSObject::kPropertiesOffset), rcx);
-  __ movp(FieldOperand(rax, JSObject::kElementsOffset), rcx);
-
-  // Set the value.
-  __ movp(FieldOperand(rax, JSValue::kValueOffset), rbx);
 
-  // Ensure the object is fully initialized.
-  STATIC_ASSERT(JSValue::kSize == 4 * kPointerSize);
-
-  // We're done. Return.
-  __ ret(0);
-
-  // The argument was not found in the number to string cache. Check
-  // if it's a string already before calling the conversion builtin.
-  Label convert_argument;
-  __ bind(&not_cached);
-  STATIC_ASSERT(kSmiTag == 0);
-  __ JumpIfSmi(rax, &convert_argument);
-  Condition is_string = masm->IsObjectStringType(rax, rbx, rcx);
-  __ j(NegateCondition(is_string), &convert_argument);
-  __ movp(rbx, rax);
-  __ IncrementCounter(counters->string_ctor_string_value(), 1);
-  __ jmp(&argument_is_string);
-
-  // Invoke the conversion builtin and put the result into rbx.
-  __ bind(&convert_argument);
-  __ IncrementCounter(counters->string_ctor_conversions(), 1);
+  // 2. Make sure rbx is a string.
   {
-    FrameScope scope(masm, StackFrame::INTERNAL);
-    __ Push(rdi);  // Preserve the function.
-    ToStringStub stub(masm->isolate());
-    __ CallStub(&stub);
-    __ Pop(rdi);
+    Label convert, done_convert;
+    __ JumpIfSmi(rbx, &convert, Label::kNear);
+    __ CmpObjectType(rbx, FIRST_NONSTRING_TYPE, rdx);
+    __ j(below, &done_convert);
+    __ bind(&convert);
+    {
+      FrameScope scope(masm, StackFrame::INTERNAL);
+      ToStringStub stub(masm->isolate());
+      __ Move(rax, rbx);
+      __ CallStub(&stub);
+      __ Move(rbx, rax);
+    }
+    __ LoadGlobalFunction(Context::STRING_FUNCTION_INDEX, rdi);
+    __ bind(&done_convert);
   }
-  __ movp(rbx, rax);
-  __ jmp(&argument_is_string);
 
-  // Load the empty string into rbx, remove the receiver from the
-  // stack, and jump back to the case where the argument is a string.
-  __ bind(&no_arguments);
-  __ LoadRoot(rbx, Heap::kempty_stringRootIndex);
-  __ PopReturnAddressTo(rcx);
-  __ leap(rsp, Operand(rsp, kPointerSize));
-  __ PushReturnAddressFrom(rcx);
-  __ jmp(&argument_is_string);
-
-  // At this point the argument is already a string. Call runtime to
-  // create a string wrapper.
-  __ bind(&gc_required);
-  __ IncrementCounter(counters->string_ctor_gc_required(), 1);
+  // 3. Allocate a JSValue wrapper for the string.
   {
-    FrameScope scope(masm, StackFrame::INTERNAL);
-    __ Push(rbx);
-    __ CallRuntime(Runtime::kNewStringWrapper, 1);
+    // ----------- S t a t e -------------
+    //  -- rbx : the first argument
+    //  -- rdi : constructor function
+    // -----------------------------------
+
+    Label allocate, done_allocate;
+    __ Allocate(JSValue::kSize, rax, rcx, no_reg, &allocate, TAG_OBJECT);
+    __ bind(&done_allocate);
+
+    // Initialize the JSValue in rax.
+    __ LoadGlobalFunctionInitialMap(rdi, rcx);
+    __ movp(FieldOperand(rax, HeapObject::kMapOffset), rcx);
+    __ LoadRoot(rcx, Heap::kEmptyFixedArrayRootIndex);
+    __ movp(FieldOperand(rax, JSObject::kPropertiesOffset), rcx);
+    __ movp(FieldOperand(rax, JSObject::kElementsOffset), rcx);
+    __ movp(FieldOperand(rax, JSValue::kValueOffset), rbx);
+    STATIC_ASSERT(JSValue::kSize == 4 * kPointerSize);
+    __ Ret();
+
+    // Fallback to the runtime to allocate in new space.
+    __ bind(&allocate);
+    {
+      FrameScope scope(masm, StackFrame::INTERNAL);
+      __ Push(rbx);
+      __ Push(Smi::FromInt(JSValue::kSize));
+      __ CallRuntime(Runtime::kAllocateInNewSpace, 1);
+      __ Pop(rbx);
+    }
+    __ LoadGlobalFunction(Context::STRING_FUNCTION_INDEX, rdi);
+    __ jmp(&done_allocate);
   }
-  __ ret(0);
 }