[generators] Fix loading of FormalParameterCount on 64bit archs.

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 757 matching lines @@
   // Dispatch on the kind of generator object.
   Label old_generator;
   __ Ldr(x3, FieldMemOperand(x4, JSFunction::kSharedFunctionInfoOffset));
   __ Ldr(x3, FieldMemOperand(x3, SharedFunctionInfo::kFunctionDataOffset));
   __ CompareObjectType(x3, x3, x3, BYTECODE_ARRAY_TYPE);
   __ B(ne, &old_generator);
 
   // New-style (ignition/turbofan) generator object
   {
     __ Ldr(x0, FieldMemOperand(x4, JSFunction::kSharedFunctionInfoOffset));
-    __ Ldr(x0,
+    __ Ldr(w0,
          FieldMemOperand(x0, SharedFunctionInfo::kFormalParameterCountOffset));
-    __ SmiUntag(x0);
     // We abuse new.target both to indicate that this is a resume call and to
     // pass in the generator object.  In ordinary calls, new.target is always
     // undefined because generator functions are non-constructable.
     __ Move(x3, x1);
     __ Move(x1, x4);
     __ Ldr(x5, FieldMemOperand(x1, JSFunction::kCodeEntryOffset));
     __ Jump(x5);
   }
 
   // Old-style (full-codegen) generator object
@@ skipping 2097 matching lines @@
   }
 }
 
 
 #undef __
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_ARM