On ia32 allow powers of two and corresponding full bit masks as safe smis.

runtime/vm/assembler_ia32.h

 // 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.
 
 #ifndef VM_ASSEMBLER_IA32_H_
 #define VM_ASSEMBLER_IA32_H_
 
 #ifndef VM_ASSEMBLER_H_
 #error Do not include assembler_ia32.h directly; use assembler.h instead.
 #endif
@@ skipping 821 matching lines @@
 
   void Comment(const char* format, ...) PRINTF_ATTRIBUTE(2, 3);
   static bool EmittingComments();
 
   const Code::Comments& GetCodeComments() const;
 
   static const char* RegisterName(Register reg);
   static const char* FpuRegisterName(FpuRegister reg);
 
   // Smis that do not fit into 17 bits (16 bits of payload) are unsafe.
+  static bool IsSafeSmi(const Object& object) {
+    if (!object.IsSmi()) {
+      return false;
+    }
+
+    if (Utils::IsInt(17, reinterpret_cast<intptr_t>(object.raw()))) {
+      return true;
+    }
+
+    // Single bit smis (powers of two) and corresponding masks are safe.
+    const intptr_t value = Smi::Cast(object).Value();
+    if (Utils::IsPowerOfTwo(value) || Utils::IsPowerOfTwo(value + 1)) {
+      return true;
+    }
+
+    return false;
+  }
   static bool IsSafe(const Object& object) {
-    return !object.IsSmi() ||
-        Utils::IsInt(17, reinterpret_cast<intptr_t>(object.raw()));
-  }
-  static bool IsSafeSmi(const Object& object) {
-    return object.IsSmi() &&
-        Utils::IsInt(17, reinterpret_cast<intptr_t>(object.raw()));
+    return !object.IsSmi() || IsSafeSmi(object);
   }
 
  private:
   class CodeComment : public ZoneAllocated {
    public:
     CodeComment(intptr_t pc_offset, const String& comment)
         : pc_offset_(pc_offset), comment_(comment) { }
 
     intptr_t pc_offset() const { return pc_offset_; }
     const String& comment() const { return comment_; }
@@ skipping 69 matching lines @@
 }
 
 
 inline void Assembler::EmitOperandSizeOverride() {
   EmitUint8(0x66);
 }
 
 }  // namespace dart
 
 #endif  // VM_ASSEMBLER_IA32_H_