Optimize AOT's switchable calls for the monomorphic case.

runtime/vm/native_arguments.h

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_NATIVE_ARGUMENTS_H_
 #define VM_NATIVE_ARGUMENTS_H_
 
 #include "platform/assert.h"
 #include "platform/memory_sanitizer.h"
 #include "vm/globals.h"
@@ skipping 89 matching lines @@
     // architectures.
     RawObject** arg_ptr = &(argv_[index]);
 #else
     RawObject** arg_ptr = &(argv_[-index]);
 #endif
     // Tell MemorySanitizer the RawObject* was initialized (by generated code).
     MSAN_UNPOISON(arg_ptr, kWordSize);
     return *arg_ptr;
   }
 
+  void SetArgAt(int index, const Object& value) const {
+    ASSERT((index >= 0) && (index < ArgCount()));
+#if defined(TARGET_ARCH_DBC)
+    // On DBC stack is growing upwards, in reverse direction from all other
+    // architectures.
+    RawObject** arg_ptr = &(argv_[index]);

[Florian Schneider, 2016/08/10 02:32:14]

Since this is not used on DBC, maybe rather make it UNREACHABLE()?

[rmacnak, 2016/08/11 00:17:49]

Remove altogether after removing monomorphic case while in the middle of
precompiling.

+#else
+    RawObject** arg_ptr = &(argv_[-index]);
+#endif
+    *arg_ptr = value.raw();
+  }
+
   bool IsNativeAutoSetupScope() const {
     return AutoSetupScopeBits::decode(argc_tag_);
   }
 
   int NativeArgCount() const {
     int function_bits = FunctionBits::decode(argc_tag_);
     return ArgCount() - NumHiddenArgs(function_bits);
   }
 
   RawObject* NativeArg0() const {
@@ skipping 134 matching lines @@
 
   Thread* thread_;  // Current thread pointer.
   intptr_t argc_tag_;  // Encodes argument count and invoked native call type.
   RawObject** argv_;  // Pointer to an array of arguments to runtime call.
   RawObject** retval_;  // Pointer to the return value area.
 };
 
 }  // namespace dart
 
 #endif  // VM_NATIVE_ARGUMENTS_H_