[es6] Introduce spec compliant IsConstructor.

src/arm64/builtins-arm64.cc

Index: src/arm64/builtins-arm64.cc
diff --git a/src/arm64/builtins-arm64.cc b/src/arm64/builtins-arm64.cc
index afa3b077f1da228a2acfa44e2fca13e64013ca36..433119801761b43f02cfb997a2268249e4284262 100644
--- a/src/arm64/builtins-arm64.cc
+++ b/src/arm64/builtins-arm64.cc
@@ -1693,6 +1693,21 @@ void Builtins::Generate_ConstructFunction(MacroAssembler* masm) {
 
 
 // static
+void Builtins::Generate_ConstructProxy(MacroAssembler* masm) {
+  // ----------- S t a t e -------------
+  //  -- x0 : the number of arguments (not including the receiver)
+  //  -- x1 : the constructor to call (checked to be a JSFunctionProxy)
+  //  -- x3 : the original constructor (either the same as the constructor or
+  //          the JSFunction on which new was invoked initially)
+  // -----------------------------------
+
+  // TODO(neis): This doesn't match the ES6 spec for [[Construct]] on proxies.
+  __ Ldr(x1, FieldMemOperand(x1, JSFunctionProxy::kConstructTrapOffset));
+  __ Jump(masm->isolate()->builtins()->Call(), RelocInfo::CODE_TARGET);
+}
+
+
+// static
 void Builtins::Generate_Construct(MacroAssembler* masm) {
   // ----------- S t a t e -------------
   //  -- x0 : the number of arguments (not including the receiver)
@@ -1701,34 +1716,34 @@ void Builtins::Generate_Construct(MacroAssembler* masm) {
   //          the JSFunction on which new was invoked initially)
   // -----------------------------------
 
-  Label non_callable, non_function;
-  __ JumpIfSmi(x1, &non_callable);
-  __ CompareObjectType(x1, x4, x5, JS_FUNCTION_TYPE);
+  // Check if target has a [[Construct]] internal method.
+  Label non_constructor;
+  __ JumpIfSmi(x1, &non_constructor);
+  __ Ldr(x4, FieldMemOperand(x1, HeapObject::kMapOffset));
+  __ Ldrb(x2, FieldMemOperand(x4, Map::kBitFieldOffset));
+  __ TestAndBranchIfAllClear(x2, 1 << Map::kIsConstructor, &non_constructor);
+
+  // Dispatch based on instance type.
+  __ CompareInstanceType(x4, x5, JS_FUNCTION_TYPE);
   __ Jump(masm->isolate()->builtins()->ConstructFunction(),
           RelocInfo::CODE_TARGET, eq);
   __ Cmp(x5, JS_FUNCTION_PROXY_TYPE);
-  __ B(ne, &non_function);
-
-  // 1. Construct of function proxy.
-  // TODO(neis): This doesn't match the ES6 spec for [[Construct]] on proxies.
-  __ Ldr(x1, FieldMemOperand(x1, JSFunctionProxy::kConstructTrapOffset));
-  __ Jump(masm->isolate()->builtins()->Call(), RelocInfo::CODE_TARGET);
+  __ Jump(masm->isolate()->builtins()->ConstructProxy(), RelocInfo::CODE_TARGET,
+          eq);
 
-  // 2. Construct of something that else, which might have a [[Construct]]
-  // internal method (if not we raise an exception).
-  __ Bind(&non_function);
-  // Check if target has a [[Call]] internal method.
-  // TODO(bmeurer): This shoud use IsConstructor once available.
-  __ Ldrb(x4, FieldMemOperand(x4, Map::kBitFieldOffset));
-  __ TestAndBranchIfAllClear(x4, 1 << Map::kIsCallable, &non_callable);
-  // Overwrite the original receiver with the (original) target.
-  __ Poke(x1, Operand(x0, LSL, kXRegSizeLog2));
-  // Let the "call_as_constructor_delegate" take care of the rest.
-  __ LoadGlobalFunction(Context::CALL_AS_CONSTRUCTOR_DELEGATE_INDEX, x1);
-  __ Jump(masm->isolate()->builtins()->CallFunction(), RelocInfo::CODE_TARGET);
+  // Called Construct on an exotic Object with a [[Construct]] internal method.
+  {
+    // Overwrite the original receiver with the (original) target.
+    __ Poke(x1, Operand(x0, LSL, kXRegSizeLog2));
+    // Let the "call_as_constructor_delegate" take care of the rest.
+    __ LoadGlobalFunction(Context::CALL_AS_CONSTRUCTOR_DELEGATE_INDEX, x1);
+    __ Jump(masm->isolate()->builtins()->CallFunction(),
+            RelocInfo::CODE_TARGET);
+  }
 
-  // 3. Construct of something that is not callable.
-  __ bind(&non_callable);
+  // Called Construct on an Object that doesn't have a [[Construct]] internal
+  // method.
+  __ bind(&non_constructor);
   {
     FrameScope scope(masm, StackFrame::INTERNAL);
     __ Push(x1);