Follow-up fix to my change to IsPowerOfTwo: Alignment of one means no alignment, not zero.

runtime/vm/stub_code_x64.cc

 // Copyright (c) 2013, 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.
 
 #include "vm/globals.h"
 #if defined(TARGET_ARCH_X64)
 
 #include "vm/assembler.h"
 #include "vm/compiler.h"
 #include "vm/dart_entry.h"
@@ skipping 43 matching lines @@
   __ movq(Address(RAX, Isolate::top_exit_frame_info_offset()), RSP);
 
   // Save current Context pointer into Isolate structure.
   __ movq(Address(RAX, Isolate::top_context_offset()), CTX);
 
   // Cache Isolate pointer into CTX while executing runtime code.
   __ movq(CTX, RAX);
 
   // Reserve space for arguments and align frame before entering C++ world.
   __ AddImmediate(RSP, Immediate(-sizeof(NativeArguments)));
-  if (OS::ActivationFrameAlignment() > 0) {
+  if (OS::ActivationFrameAlignment() > 1) {
     __ andq(RSP, Immediate(~(OS::ActivationFrameAlignment() - 1)));
   }
 
   // Pass NativeArguments structure by value and call runtime.
   __ movq(Address(RSP, isolate_offset), CTX);  // Set isolate in NativeArgs.
   // There are no runtime calls to closures, so we do not need to set the tag
   // bits kClosureFunctionBit and kInstanceFunctionBit in argc_tag_.
   __ movq(Address(RSP, argc_tag_offset), R10);  // Set argc in NativeArguments.
   __ leaq(RAX, Address(RBP, R10, TIMES_8, 1 * kWordSize));  // Compute argv.
   __ movq(Address(RSP, argv_offset), RAX);  // Set argv in NativeArguments.
@@ skipping 69 matching lines @@
   // Save current Context pointer into Isolate structure.
   __ movq(Address(R8, Isolate::top_context_offset()), CTX);
 
   // Cache Isolate pointer into CTX while executing native code.
   __ movq(CTX, R8);
 
   // Reserve space for the native arguments structure passed on the stack (the
   // outgoing pointer parameter to the native arguments structure is passed in
   // RDI) and align frame before entering the C++ world.
   __ AddImmediate(RSP, Immediate(-sizeof(NativeArguments)));
-  if (OS::ActivationFrameAlignment() > 0) {
+  if (OS::ActivationFrameAlignment() > 1) {
     __ andq(RSP, Immediate(~(OS::ActivationFrameAlignment() - 1)));
   }
 
   // Pass NativeArguments structure by value and call native function.
   __ movq(Address(RSP, isolate_offset), CTX);  // Set isolate in NativeArgs.
   __ movq(Address(RSP, argc_tag_offset), R10);  // Set argc in NativeArguments.
   __ movq(Address(RSP, argv_offset), RAX);  // Set argv in NativeArguments.
   __ leaq(RAX, Address(RBP, 2 * kWordSize));  // Compute return value addr.
   __ movq(Address(RSP, retval_offset), RAX);  // Set retval in NativeArguments.
   __ movq(RDI, RSP);  // Pass the pointer to the NativeArguments.
@@ skipping 48 matching lines @@
   // Save current Context pointer into Isolate structure.
   __ movq(Address(R8, Isolate::top_context_offset()), CTX);
 
   // Cache Isolate pointer into CTX while executing native code.
   __ movq(CTX, R8);
 
   // Reserve space for the native arguments structure passed on the stack (the
   // outgoing pointer parameter to the native arguments structure is passed in
   // RDI) and align frame before entering the C++ world.
   __ AddImmediate(RSP, Immediate(-sizeof(NativeArguments)));
-  if (OS::ActivationFrameAlignment() > 0) {
+  if (OS::ActivationFrameAlignment() > 1) {
     __ andq(RSP, Immediate(~(OS::ActivationFrameAlignment() - 1)));
   }
 
   // Pass NativeArguments structure by value and call native function.
   __ movq(Address(RSP, isolate_offset), CTX);  // Set isolate in NativeArgs.
   __ movq(Address(RSP, argc_tag_offset), R10);  // Set argc in NativeArguments.
   __ movq(Address(RSP, argv_offset), RAX);  // Set argv in NativeArguments.
   __ leaq(RAX, Address(RBP, 2 * kWordSize));  // Compute return value addr.
   __ movq(Address(RSP, retval_offset), RAX);  // Set retval in NativeArguments.
   __ movq(RDI, RSP);  // Pass the pointer to the NativeArguments.
@@ skipping 1994 matching lines @@
   __ movq(right, Address(RSP, 3 * kWordSize));
   GenerateIdenticalWithNumberCheckStub(assembler, left, right);
   __ popq(right);
   __ popq(left);
   __ ret();
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_X64