Option to truncate integers to 64 bits, part 1 (core VM changes)

runtime/vm/intermediate_language.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/intermediate_language.h"
 
 #include "vm/bit_vector.h"
 #include "vm/bootstrap.h"
 #include "vm/compiler.h"
 #include "vm/constant_propagator.h"
@@ skipping 1800 matching lines @@
     case Token::kDIV:
       break;
     default:
       UNREACHABLE();
   }
 
   if (!result.IsNull()) {
     if (is_truncating()) {
       int64_t truncated = result.AsTruncatedInt64Value();
       truncated &= RepresentationMask(representation());
-      result = Integer::New(truncated);
+      result = Integer::New(truncated, Heap::kOld);

[siva, 2017/07/07 23:11:20]

Why is it necessary to allocate in old space? the value seems to be
canonicalized below which will ensure it gets to the old space.

[alexmarkov, 2017/07/10 16:58:12]

It is a bug fix. This code is used to do constant folding in the background
compilation thread, which is unable to allocate objects in the young generation
(causes assertion failure).

       ASSERT(IsRepresentable(result, representation()));
     } else if (!IsRepresentable(result, representation())) {
       // If this operation is not truncating it would deoptimize on overflow.
       // Check that we match this behavior and don't produce a value that is
       // larger than something this operation can produce. We could have
       // specialized instructions that use this value under this assumption.
       return Integer::null();
     }
     result ^= result.CheckAndCanonicalize(thread, NULL);
   }
@@ skipping 2569 matching lines @@
                      "native function '%s' (%" Pd " arguments) cannot be found",
                      native_name().ToCString(), function().NumParameters());
   }
   set_is_auto_scope(auto_setup_scope);
   set_native_c_function(native_function);
 }
 
 #undef __
 
 }  // namespace dart