Reland [arm64] Improve some new builtins.

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 898c7ba331af76081bb3aeab87547396f8f6dc31..6f57d37a3d5bb67357dac3898e4d28fdf7046917 100644
--- a/src/arm64/builtins-arm64.cc
+++ b/src/arm64/builtins-arm64.cc
@@ -1403,54 +1403,71 @@ void Builtins::Generate_DatePrototype_GetField(MacroAssembler* masm,
 // static
 void Builtins::Generate_FunctionPrototypeApply(MacroAssembler* masm) {
   // ----------- S t a t e -------------
-  //  -- r0     : argc
-  //  -- sp[0]  : argArray
-  //  -- sp[8]  : thisArg
-  //  -- sp[16] : receiver
+  //  -- x0       : argc
+  //  -- jssp[0]  : argArray (if argc == 2)
+  //  -- jssp[8]  : thisArg  (if argc >= 1)
+  //  -- jssp[16] : receiver
   // -----------------------------------
   ASM_LOCATION("Builtins::Generate_FunctionPrototypeApply");
 
+  Register argc = x0;
+  Register arg_array = x0;
+  Register receiver = x1;
+  Register this_arg = x2;
+  Register undefined_value = x3;
+  Register null_value = x4;
+
+  __ LoadRoot(undefined_value, Heap::kUndefinedValueRootIndex);
+  __ LoadRoot(null_value, Heap::kNullValueRootIndex);
+
   // 1. Load receiver into x1, argArray into x0 (if present), remove all
   // arguments from the stack (including the receiver), and push thisArg (if
   // present) instead.
   {
-    Label done;
-    __ LoadRoot(x2, Heap::kUndefinedValueRootIndex);
-    __ Mov(x3, x2);
-    __ Peek(x1, Operand(x0, LSL, kPointerSizeLog2));  // receiver
-    __ Subs(x4, x0, 1);
-    __ B(lt, &done);
-    __ Peek(x2, Operand(x4, LSL, kPointerSizeLog2));  // thisArg
-    __ Subs(x4, x4, 1);
-    __ B(lt, &done);
-    __ Peek(x3, Operand(x4, LSL, kPointerSizeLog2));  // argArray
-    __ Bind(&done);
-    __ Drop(x0);
-    __ Poke(x2, 0);
-    __ Mov(x0, x3);
+    // Claim (2 - argc) dummy arguments from the stack, to put the stack in a
+    // consistent state for a simple pop operation.
+    __ Claim(2);
+    __ Drop(argc);
+
+    // ----------- S t a t e -------------
+    //  -- x0       : argc
+    //  -- jssp[0]  : argArray (dummy value if argc <= 1)
+    //  -- jssp[8]  : thisArg  (dummy value if argc == 0)
+    //  -- jssp[16] : receiver
+    // -----------------------------------
+    __ Cmp(argc, 1);
+    __ Pop(arg_array, this_arg);               // Overwrites argc.
+    __ CmovX(this_arg, undefined_value, lo);   // undefined if argc == 0.
+    __ CmovX(arg_array, undefined_value, ls);  // undefined if argc <= 1.
+
+    __ Peek(receiver, 0);
+    __ Poke(this_arg, 0);
   }
 
   // ----------- S t a t e -------------
-  //  -- x0    : argArray
-  //  -- x1    : receiver
-  //  -- sp[0] : thisArg
+  //  -- x0      : argArray
+  //  -- x1      : receiver
+  //  -- x3      : undefined root value
+  //  -- jssp[0] : thisArg
   // -----------------------------------
 
   // 2. Make sure the receiver is actually callable.
   Label receiver_not_callable;
-  __ JumpIfSmi(x1, &receiver_not_callable);
-  __ Ldr(x4, FieldMemOperand(x1, HeapObject::kMapOffset));
-  __ Ldrb(x4, FieldMemOperand(x4, Map::kBitFieldOffset));
-  __ TestAndBranchIfAllClear(x4, 1 << Map::kIsCallable, &receiver_not_callable);
+  __ JumpIfSmi(receiver, &receiver_not_callable);
+  __ Ldr(x10, FieldMemOperand(receiver, HeapObject::kMapOffset));
+  __ Ldrb(w10, FieldMemOperand(x10, Map::kBitFieldOffset));
+  __ TestAndBranchIfAllClear(x10, 1 << Map::kIsCallable,
+                             &receiver_not_callable);
 
   // 3. Tail call with no arguments if argArray is null or undefined.
   Label no_arguments;
-  __ JumpIfRoot(x0, Heap::kNullValueRootIndex, &no_arguments);
-  __ JumpIfRoot(x0, Heap::kUndefinedValueRootIndex, &no_arguments);
+  __ Cmp(arg_array, null_value);
+  __ Ccmp(arg_array, undefined_value, ZFlag, ne);
+  __ B(eq, &no_arguments);
 
   // 4a. Apply the receiver to the given argArray (passing undefined for
-  // new.target).
-  __ LoadRoot(x3, Heap::kUndefinedValueRootIndex);
+  // new.target in x3).
+  DCHECK(undefined_value.Is(x3));
   __ Jump(masm->isolate()->builtins()->Apply(), RelocInfo::CODE_TARGET);
 
   // 4b. The argArray is either null or undefined, so we tail call without any
@@ -1458,13 +1475,14 @@ void Builtins::Generate_FunctionPrototypeApply(MacroAssembler* masm) {
   __ Bind(&no_arguments);
   {
     __ Mov(x0, 0);
+    DCHECK(receiver.Is(x1));
     __ Jump(masm->isolate()->builtins()->Call(), RelocInfo::CODE_TARGET);
   }
 
   // 4c. The receiver is not callable, throw an appropriate TypeError.
   __ Bind(&receiver_not_callable);
   {
-    __ Poke(x1, 0);
+    __ Poke(receiver, 0);
     __ TailCallRuntime(Runtime::kThrowApplyNonFunction);
   }
 }
@@ -1519,59 +1537,70 @@ void Builtins::Generate_FunctionPrototypeCall(MacroAssembler* masm) {
 
 void Builtins::Generate_ReflectApply(MacroAssembler* masm) {
   // ----------- S t a t e -------------
-  //  -- x0     : argc
-  //  -- sp[0]  : argumentsList
-  //  -- sp[8]  : thisArgument
-  //  -- sp[16] : target
-  //  -- sp[24] : receiver
+  //  -- x0       : argc
+  //  -- jssp[0]  : argumentsList (if argc == 3)
+  //  -- jssp[8]  : thisArgument  (if argc >= 2)
+  //  -- jssp[16] : target        (if argc >= 1)
+  //  -- jssp[24] : receiver
   // -----------------------------------
   ASM_LOCATION("Builtins::Generate_ReflectApply");
 
+  Register argc = x0;
+  Register arguments_list = x0;
+  Register target = x1;
+  Register this_argument = x2;
+  Register undefined_value = x3;
+
+  __ LoadRoot(undefined_value, Heap::kUndefinedValueRootIndex);
+
   // 1. Load target into x1 (if present), argumentsList into x0 (if present),
   // remove all arguments from the stack (including the receiver), and push
   // thisArgument (if present) instead.
   {
-    Label done;
-    __ LoadRoot(x1, Heap::kUndefinedValueRootIndex);
-    __ Mov(x2, x1);
-    __ Mov(x3, x1);
-    __ Subs(x4, x0, 1);
-    __ B(lt, &done);
-    __ Peek(x1, Operand(x4, LSL, kPointerSizeLog2));  // target
-    __ Subs(x4, x4, 1);
-    __ B(lt, &done);
-    __ Peek(x2, Operand(x4, LSL, kPointerSizeLog2));  // thisArgument
-    __ Subs(x4, x4, 1);
-    __ B(lt, &done);
-    __ Peek(x3, Operand(x4, LSL, kPointerSizeLog2));  // argumentsList
-    __ Bind(&done);
-    __ Drop(x0);
-    __ Poke(x2, 0);
-    __ Mov(x0, x3);
+    // Claim (3 - argc) dummy arguments from the stack, to put the stack in a
+    // consistent state for a simple pop operation.
+    __ Claim(3);
+    __ Drop(argc);
+
+    // ----------- S t a t e -------------
+    //  -- x0       : argc
+    //  -- jssp[0]  : argumentsList (dummy value if argc <= 2)
+    //  -- jssp[8]  : thisArgument  (dummy value if argc <= 1)
+    //  -- jssp[16] : target        (dummy value if argc == 0)
+    //  -- jssp[24] : receiver
+    // -----------------------------------
+    __ Adds(x10, argc, 0);  // Preserve argc, and set the Z flag if it is zero.
+    __ Pop(arguments_list, this_argument, target);  // Overwrites argc.
+    __ CmovX(target, undefined_value, eq);          // undefined if argc == 0.
+    __ Cmp(x10, 2);
+    __ CmovX(this_argument, undefined_value, lo);   // undefined if argc <= 1.
+    __ CmovX(arguments_list, undefined_value, ls);  // undefined if argc <= 2.
+
+    __ Poke(this_argument, 0);  // Overwrite receiver.
   }
 
   // ----------- S t a t e -------------
-  //  -- x0    : argumentsList
-  //  -- x1    : target
-  //  -- sp[0] : thisArgument
+  //  -- x0      : argumentsList
+  //  -- x1      : target
+  //  -- jssp[0] : thisArgument
   // -----------------------------------
 
   // 2. Make sure the target is actually callable.
   Label target_not_callable;
-  __ JumpIfSmi(x1, &target_not_callable);
-  __ Ldr(x4, FieldMemOperand(x1, HeapObject::kMapOffset));
-  __ Ldrb(x4, FieldMemOperand(x4, Map::kBitFieldOffset));
-  __ TestAndBranchIfAllClear(x4, 1 << Map::kIsCallable, &target_not_callable);
+  __ JumpIfSmi(target, &target_not_callable);
+  __ Ldr(x10, FieldMemOperand(target, HeapObject::kMapOffset));
+  __ Ldr(x10, FieldMemOperand(x10, Map::kBitFieldOffset));
+  __ TestAndBranchIfAllClear(x10, 1 << Map::kIsCallable, &target_not_callable);
 
   // 3a. Apply the target to the given argumentsList (passing undefined for
-  // new.target).
-  __ LoadRoot(x3, Heap::kUndefinedValueRootIndex);
+  // new.target in x3).
+  DCHECK(undefined_value.Is(x3));
   __ Jump(masm->isolate()->builtins()->Apply(), RelocInfo::CODE_TARGET);
 
   // 3b. The target is not callable, throw an appropriate TypeError.
   __ Bind(&target_not_callable);
   {
-    __ Poke(x1, 0);
+    __ Poke(target, 0);
     __ TailCallRuntime(Runtime::kThrowApplyNonFunction);
   }
 }
@@ -1579,59 +1608,70 @@ void Builtins::Generate_ReflectApply(MacroAssembler* masm) {
 
 void Builtins::Generate_ReflectConstruct(MacroAssembler* masm) {
   // ----------- S t a t e -------------
-  //  -- x0     : argc
-  //  -- sp[0]  : new.target (optional)
-  //  -- sp[8]  : argumentsList
-  //  -- sp[16] : target
-  //  -- sp[24] : receiver
+  //  -- x0       : argc
+  //  -- jssp[0]  : new.target (optional)
+  //  -- jssp[8]  : argumentsList
+  //  -- jssp[16] : target
+  //  -- jssp[24] : receiver
   // -----------------------------------
   ASM_LOCATION("Builtins::Generate_ReflectConstruct");
 
+  Register argc = x0;
+  Register arguments_list = x0;
+  Register target = x1;
+  Register new_target = x3;
+  Register undefined_value = x4;
+
+  __ LoadRoot(undefined_value, Heap::kUndefinedValueRootIndex);
+
   // 1. Load target into x1 (if present), argumentsList into x0 (if present),
   // new.target into x3 (if present, otherwise use target), remove all
   // arguments from the stack (including the receiver), and push thisArgument
   // (if present) instead.
   {
-    Label done;
-    __ LoadRoot(x1, Heap::kUndefinedValueRootIndex);
-    __ Mov(x2, x1);
-    __ Poke(x2, Operand(x0, LSL, kPointerSizeLog2));  // receiver
-    __ Subs(x4, x0, 1);
-    __ B(lt, &done);
-    __ Peek(x1, Operand(x4, LSL, kPointerSizeLog2));  // target
-    __ Mov(x3, x1);  // new.target defaults to target
-    __ Subs(x4, x4, 1);
-    __ B(lt, &done);
-    __ Peek(x2, Operand(x4, LSL, kPointerSizeLog2));  // argumentsList
-    __ Subs(x4, x4, 1);
-    __ B(lt, &done);
-    __ Peek(x3, Operand(x4, LSL, kPointerSizeLog2));  // new.target
-    __ Bind(&done);
-    __ Drop(x0);
-    __ Mov(x0, x2);
+    // Claim (3 - argc) dummy arguments from the stack, to put the stack in a
+    // consistent state for a simple pop operation.
+    __ Claim(3);
+    __ Drop(argc);
+
+    // ----------- S t a t e -------------
+    //  -- x0       : argc
+    //  -- jssp[0]  : new.target    (dummy value if argc <= 2)
+    //  -- jssp[8]  : argumentsList (dummy value if argc <= 1)
+    //  -- jssp[16] : target        (dummy value if argc == 0)
+    //  -- jssp[24] : receiver
+    // -----------------------------------
+    __ Adds(x10, argc, 0);  // Preserve argc, and set the Z flag if it is zero.
+    __ Pop(new_target, arguments_list, target);  // Overwrites argc.
+    __ CmovX(target, undefined_value, eq);       // undefined if argc == 0.
+    __ Cmp(x10, 2);
+    __ CmovX(arguments_list, undefined_value, lo);  // undefined if argc <= 1.
+    __ CmovX(new_target, target, ls);               // target if argc <= 2.
+
+    __ Poke(undefined_value, 0);  // Overwrite receiver.
   }
 
   // ----------- S t a t e -------------
-  //  -- x0    : argumentsList
-  //  -- x3    : new.target
-  //  -- x1    : target
-  //  -- sp[0] : receiver (undefined)
+  //  -- x0      : argumentsList
+  //  -- x1      : target
+  //  -- x3      : new.target
+  //  -- jssp[0] : receiver (undefined)
   // -----------------------------------
 
   // 2. Make sure the target is actually a constructor.
   Label target_not_constructor;
-  __ JumpIfSmi(x1, &target_not_constructor);
-  __ Ldr(x4, FieldMemOperand(x1, HeapObject::kMapOffset));
-  __ Ldrb(x4, FieldMemOperand(x4, Map::kBitFieldOffset));
-  __ TestAndBranchIfAllClear(x4, 1 << Map::kIsConstructor,
+  __ JumpIfSmi(target, &target_not_constructor);
+  __ Ldr(x10, FieldMemOperand(target, HeapObject::kMapOffset));
+  __ Ldrb(x10, FieldMemOperand(x10, Map::kBitFieldOffset));
+  __ TestAndBranchIfAllClear(x10, 1 << Map::kIsConstructor,
                              &target_not_constructor);
 
-  // 3. Make sure the target is actually a constructor.
+  // 3. Make sure the new.target is actually a constructor.
   Label new_target_not_constructor;
-  __ JumpIfSmi(x3, &new_target_not_constructor);
-  __ Ldr(x4, FieldMemOperand(x3, HeapObject::kMapOffset));
-  __ Ldrb(x4, FieldMemOperand(x4, Map::kBitFieldOffset));
-  __ TestAndBranchIfAllClear(x4, 1 << Map::kIsConstructor,
+  __ JumpIfSmi(new_target, &new_target_not_constructor);
+  __ Ldr(x10, FieldMemOperand(new_target, HeapObject::kMapOffset));
+  __ Ldrb(x10, FieldMemOperand(x10, Map::kBitFieldOffset));
+  __ TestAndBranchIfAllClear(x10, 1 << Map::kIsConstructor,
                              &new_target_not_constructor);
 
   // 4a. Construct the target with the given new.target and argumentsList.
@@ -1640,14 +1680,14 @@ void Builtins::Generate_ReflectConstruct(MacroAssembler* masm) {
   // 4b. The target is not a constructor, throw an appropriate TypeError.
   __ Bind(&target_not_constructor);
   {
-    __ Poke(x1, 0);
+    __ Poke(target, 0);
     __ TailCallRuntime(Runtime::kThrowCalledNonCallable);
   }
 
   // 4c. The new.target is not a constructor, throw an appropriate TypeError.
   __ Bind(&new_target_not_constructor);
   {
-    __ Poke(x3, 0);
+    __ Poke(new_target, 0);
     __ TailCallRuntime(Runtime::kThrowCalledNonCallable);
   }
 }
@@ -1703,72 +1743,81 @@ static void LeaveArgumentsAdaptorFrame(MacroAssembler* masm) {
 // static
 void Builtins::Generate_Apply(MacroAssembler* masm) {
   // ----------- S t a t e -------------
-  //  -- x0    : argumentsList
-  //  -- x1    : target
-  //  -- x3    : new.target (checked to be constructor or undefined)
-  //  -- sp[0] : thisArgument
+  //  -- x0      : argumentsList
+  //  -- x1      : target
+  //  -- x3      : new.target (checked to be constructor or undefined)
+  //  -- jssp[0] : thisArgument
   // -----------------------------------
 
+  Register arguments_list = x0;
+  Register target = x1;
+  Register new_target = x3;
+
+  Register args = x0;
+  Register len = x2;
+
   // Create the list of arguments from the array-like argumentsList.
   {
     Label create_arguments, create_array, create_runtime, done_create;
-    __ JumpIfSmi(x0, &create_runtime);
+    __ JumpIfSmi(arguments_list, &create_runtime);
 
-    // Load the map of argumentsList into x2.
-    __ Ldr(x2, FieldMemOperand(x0, HeapObject::kMapOffset));
+    // Load native context.
+    Register native_context = x4;
+    __ Ldr(native_context, NativeContextMemOperand());
 
-    // Load native context into x4.
-    __ Ldr(x4, NativeContextMemOperand());
+    // Load the map of argumentsList.
+    Register arguments_list_map = x2;
+    __ Ldr(arguments_list_map,
+           FieldMemOperand(arguments_list, HeapObject::kMapOffset));
 
     // Check if argumentsList is an (unmodified) arguments object.
-    __ Ldr(x5, ContextMemOperand(x4, Context::SLOPPY_ARGUMENTS_MAP_INDEX));
-    __ Cmp(x5, x2);
-    __ B(eq, &create_arguments);
-    __ Ldr(x5, ContextMemOperand(x4, Context::STRICT_ARGUMENTS_MAP_INDEX));
-    __ Cmp(x5, x2);
+    __ Ldr(x10, ContextMemOperand(native_context,
+                                  Context::SLOPPY_ARGUMENTS_MAP_INDEX));
+    __ Ldr(x11, ContextMemOperand(native_context,
+                                  Context::STRICT_ARGUMENTS_MAP_INDEX));
+    __ Cmp(arguments_list_map, x10);
+    __ Ccmp(arguments_list_map, x11, ZFlag, ne);
     __ B(eq, &create_arguments);
 
     // Check if argumentsList is a fast JSArray.
-    __ CompareInstanceType(x2, x4, JS_ARRAY_TYPE);
+    __ CompareInstanceType(arguments_list_map, native_context, JS_ARRAY_TYPE);
     __ B(eq, &create_array);
 
     // Ask the runtime to create the list (actually a FixedArray).
     __ Bind(&create_runtime);
     {
       FrameScope scope(masm, StackFrame::INTERNAL);
-      __ Push(x1, x3, x0);
+      __ Push(target, new_target, arguments_list);
       __ CallRuntime(Runtime::kCreateListFromArrayLike);
-      __ Pop(x3, x1);
-      __ Ldrsw(x2, UntagSmiFieldMemOperand(x0, FixedArray::kLengthOffset));
+      __ Pop(new_target, target);
+      __ Ldrsw(len, UntagSmiFieldMemOperand(arguments_list,
+                                            FixedArray::kLengthOffset));
     }
     __ B(&done_create);
 
     // Try to create the list from an arguments object.
     __ Bind(&create_arguments);
-    __ Ldr(x2,
-           FieldMemOperand(x0, JSObject::kHeaderSize +
-                                   Heap::kArgumentsLengthIndex * kPointerSize));
-    __ Ldr(x4, FieldMemOperand(x0, JSObject::kElementsOffset));
-    __ Ldr(x5, FieldMemOperand(x4, FixedArray::kLengthOffset));
-    __ Cmp(x2, x4);
-    __ B(ne, &create_runtime);
-    __ SmiUntag(x2);
-    __ Mov(x0, x4);
+    __ Ldrsw(len, UntagSmiFieldMemOperand(
+                      arguments_list,
+                      JSObject::kHeaderSize +
+                          Heap::kArgumentsLengthIndex * kPointerSize));
+    __ Ldr(x10, FieldMemOperand(arguments_list, JSObject::kElementsOffset));
+    __ Ldrsw(x11, UntagSmiFieldMemOperand(x10, FixedArray::kLengthOffset));
+    __ CompareAndBranch(len, x11, ne, &create_runtime);
+    __ Mov(args, x10);
     __ B(&done_create);
 
     // Try to create the list from a JSArray object.
     __ Bind(&create_array);
-    __ Ldr(x2, FieldMemOperand(x2, Map::kBitField2Offset));
-    __ DecodeField<Map::ElementsKindBits>(x2);
+    __ Ldr(x10, FieldMemOperand(arguments_list_map, Map::kBitField2Offset));
+    __ DecodeField<Map::ElementsKindBits>(x10);
     STATIC_ASSERT(FAST_SMI_ELEMENTS == 0);
-    STATIC_ASSERT(FAST_HOLEY_SMI_ELEMENTS == 1);
     STATIC_ASSERT(FAST_ELEMENTS == 2);
-    __ Cmp(x2, FAST_ELEMENTS);
-    __ B(hi, &create_runtime);
-    __ Cmp(x2, FAST_HOLEY_SMI_ELEMENTS);
-    __ B(eq, &create_runtime);
-    __ Ldrsw(x2, UntagSmiFieldMemOperand(x0, JSArray::kLengthOffset));
-    __ Ldr(x0, FieldMemOperand(x0, JSArray::kElementsOffset));
+    // Branch for anything that's not FAST_{SMI_}ELEMENTS.
+    __ TestAndBranchIfAnySet(x10, ~FAST_ELEMENTS, &create_runtime);
+    __ Ldrsw(len,
+             UntagSmiFieldMemOperand(arguments_list, JSArray::kLengthOffset));
+    __ Ldr(args, FieldMemOperand(arguments_list, JSArray::kElementsOffset));
 
     __ Bind(&done_create);
   }
@@ -1781,41 +1830,53 @@ void Builtins::Generate_Apply(MacroAssembler* masm) {
     __ LoadRoot(x10, Heap::kRealStackLimitRootIndex);
     // Make x10 the space we have left. The stack might already be overflowed
     // here which will cause x10 to become negative.
-    __ Sub(x10, jssp, x10);
+    __ Sub(x10, masm->StackPointer(), x10);
     // Check if the arguments will overflow the stack.
-    __ Cmp(x10, Operand(x2, LSL, kPointerSizeLog2));
+    __ Cmp(x10, Operand(len, LSL, kPointerSizeLog2));
     __ B(gt, &done);  // Signed comparison.
     __ TailCallRuntime(Runtime::kThrowStackOverflow);
     __ Bind(&done);
   }
 
   // ----------- S t a t e -------------
-  //  -- x1    : target
-  //  -- x0    : args (a FixedArray built from argumentsList)
-  //  -- x2    : len (number of elements to push from args)
-  //  -- x3    : new.target (checked to be constructor or undefined)
-  //  -- sp[0] : thisArgument
+  //  -- x0      : args (a FixedArray built from argumentsList)
+  //  -- x1      : target
+  //  -- x2      : len (number of elements to push from args)
+  //  -- x3      : new.target (checked to be constructor or undefined)
+  //  -- jssp[0] : thisArgument
   // -----------------------------------
 
   // Push arguments onto the stack (thisArgument is already on the stack).
   {
-    __ Mov(x4, 0);
     Label done, loop;
+    Register src = x4;
+
+    __ Add(src, args, FixedArray::kHeaderSize - kHeapObjectTag);
+    __ Mov(x0, len);  // The 'len' argument for Call() or Construct().
+    __ Cbz(len, &done);
+    __ Claim(len);
     __ Bind(&loop);
-    __ Cmp(x4, x2);
-    __ B(eq, &done);
-    __ Add(x10, x0, Operand(x4, LSL, kPointerSizeLog2));
-    __ Ldr(x10, FieldMemOperand(x10, FixedArray::kHeaderSize));
-    __ Push(x10);
-    __ Add(x4, x4, 1);
-    __ B(&loop);
+    __ Sub(len, len, 1);
+    __ Ldr(x10, MemOperand(src, kPointerSize, PostIndex));
+    __ Poke(x10, Operand(len, LSL, kPointerSizeLog2));
+    __ Cbnz(len, &loop);
     __ Bind(&done);
-    __ Mov(x0, x4);
   }
 
+  // ----------- S t a t e -------------
+  //  -- x0              : argument count (len)
+  //  -- x1              : target
+  //  -- x3              : new.target (checked to be constructor or undefined)
+  //  -- jssp[0]         : args[len-1]
+  //  -- jssp[8]         : args[len-2]
+  //      ...            :  ...
+  //  -- jssp[8*(len-2)] : args[1]
+  //  -- jssp[8*(len-1)] : args[0]
+  // -----------------------------------
+
   // Dispatch to Call or Construct depending on whether new.target is undefined.
   {
-    __ CompareRoot(x3, Heap::kUndefinedValueRootIndex);
+    __ CompareRoot(new_target, Heap::kUndefinedValueRootIndex);
     __ Jump(masm->isolate()->builtins()->Call(), RelocInfo::CODE_TARGET, eq);
     __ Jump(masm->isolate()->builtins()->Construct(), RelocInfo::CODE_TARGET);
   }
@@ -1825,6 +1886,7 @@ void Builtins::Generate_Apply(MacroAssembler* masm) {
 // static
 void Builtins::Generate_CallFunction(MacroAssembler* masm,
                                      ConvertReceiverMode mode) {
+  ASM_LOCATION("Builtins::Generate_CallFunction");
   // ----------- S t a t e -------------
   //  -- x0 : the number of arguments (not including the receiver)
   //  -- x1 : the function to call (checked to be a JSFunction)