Revert a change to an integer size

runtime/vm/object.cc

 // 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.
 
 #include "vm/object.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/assembler.h"
 #include "vm/become.h"
@@ skipping 4526 matching lines @@
   hash += hash << 10;
   hash ^= hash >> 6;  // Logical shift, unsigned hash.
   return hash;
 }
 
 
 static uint32_t FinalizeHash(uint32_t hash, intptr_t hashbits) {
   hash += hash << 3;
   hash ^= hash >> 11;  // Logical shift, unsigned hash.
   hash += hash << 15;
-  hash &= (static_cast<uint32_t>(1) << hashbits) - 1;
+  // FinalizeHash gets called with values for hashbits that are bigger than 31
+  // (like kBitsPerWord - 1).  Therefore we are careful to use a type
+  // (uintptr_t) big enough to avoid undefined behavior with the left shift.
+  hash &= (static_cast<uintptr_t>(1) << hashbits) - 1;
   return (hash == 0) ? 1 : hash;
 }
 
 
 intptr_t TypeArguments::ComputeHash() const {
   if (IsNull()) return 0;
   const intptr_t num_types = Length();
   if (IsRaw(0, num_types)) return 0;
   uint32_t result = 0;
   AbstractType& type = AbstractType::Handle();
@@ skipping 18527 matching lines @@
   return UserTag::null();
 }
 
 
 const char* UserTag::ToCString() const {
   const String& tag_label = String::Handle(label());
   return tag_label.ToCString();
 }
 
 }  // namespace dart