[builtins] One runtime fallback is enough for the String constructor.

src/arm64/builtins-arm64.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #if V8_TARGET_ARCH_ARM64
 
 #include "src/arm64/frames-arm64.h"
 #include "src/codegen.h"
 #include "src/debug/debug.h"
 #include "src/deoptimizer.h"
@@ skipping 229 matching lines @@
       ToStringStub stub(masm->isolate());
       __ Push(x1, x3);
       __ Move(x0, x2);
       __ CallStub(&stub);
       __ Move(x2, x0);
       __ Pop(x1, x3);
     }
     __ Bind(&done_convert);
   }
 
-  // 3. Allocate a JSValue wrapper for the string.
+  // 3. Check if original constructor and constructor differ.
+  Label new_object;
+  __ Cmp(x1, x3);
+  __ B(ne, &new_object);
+
+  // 4. Allocate a JSValue wrapper for the string.
   {
     // ----------- S t a t e -------------
     //  -- x2 : the first argument
     //  -- x1 : constructor function
     //  -- x3 : original constructor
     //  -- lr : return address
     // -----------------------------------
-
-    Label allocate, done_allocate, rt_call;
-
-    // Fall back to runtime if the original constructor and function differ.
-    __ cmp(x1, x3);
-    __ B(ne, &rt_call);
-
-    __ Allocate(JSValue::kSize, x0, x3, x4, &allocate, TAG_OBJECT);
-    __ Bind(&done_allocate);
+    __ Allocate(JSValue::kSize, x0, x4, x5, &new_object, TAG_OBJECT);
 
     // Initialize the JSValue in eax.
     __ LoadGlobalFunctionInitialMap(x1, x3, x4);
     __ Str(x3, FieldMemOperand(x0, HeapObject::kMapOffset));
     __ LoadRoot(x3, Heap::kEmptyFixedArrayRootIndex);
     __ Str(x3, FieldMemOperand(x0, JSObject::kPropertiesOffset));
     __ Str(x3, FieldMemOperand(x0, JSObject::kElementsOffset));
     __ Str(x2, FieldMemOperand(x0, JSValue::kValueOffset));
     STATIC_ASSERT(JSValue::kSize == 4 * kPointerSize);
     __ Ret();
+  }
 
-    // Fallback to the runtime to allocate in new space.
-    __ Bind(&allocate);
-    {
-      FrameScope scope(masm, StackFrame::INTERNAL);
-      __ Push(x1, x2);
-      __ Push(Smi::FromInt(JSValue::kSize));
-      __ CallRuntime(Runtime::kAllocateInNewSpace, 1);
-      __ Pop(x2, x1);
-    }
-    __ B(&done_allocate);
-
-    // Fallback to the runtime to create new object.
-    __ bind(&rt_call);
-    {
-      FrameScope scope(masm, StackFrame::INTERNAL);
-      __ Push(x1, x2, x1, x3);  // constructor function, original constructor
-      __ CallRuntime(Runtime::kNewObject, 2);
-      __ Pop(x2, x1);
-    }
-    __ Str(x2, FieldMemOperand(x0, JSValue::kValueOffset));
-    __ Ret();
+  // 5. Fallback to the runtime to create new object.
+  __ bind(&new_object);
+  {
+    FrameScope scope(masm, StackFrame::INTERNAL);
+    __ Push(x2, x1);  // first argument, constructor
+    __ Push(x1, x3);  // constructor, original constructor
+    __ CallRuntime(Runtime::kNewObject, 2);
+    __ Pop(x1, x2);
   }
+  __ Str(x2, FieldMemOperand(x0, JSValue::kValueOffset));
+  __ Ret();
 }
 
 
 static void CallRuntimePassFunction(MacroAssembler* masm,
                                     Runtime::FunctionId function_id) {
   FrameScope scope(masm, StackFrame::INTERNAL);
   //   - Push a copy of the function onto the stack.
   //   - Push another copy as a parameter to the runtime call.
   __ Push(x1, x1);
 
@@ skipping 1722 matching lines @@
   }
 }
 
 
 #undef __
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_ARM