Reland "VM: Handle null-comparisons in the flow graph type propagation"

runtime/lib/integers.dart

 // 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.
 
+// This marker interface represents 64-bit integers in the compiler for type
+// propagation and range analysis.  It is implemented by _Smi and _Mint.
+abstract class _int64 implements int {}
+
 abstract class _IntegerImplementation {
   // The Dart class _Bigint extending _IntegerImplementation requires a
   // default constructor.
 
   num operator +(num other) {
     var result = other._addFromInteger(this);
     if (result != null) return result;
     return other._toBigint()._addFromInteger(this);
   }
 
@@ skipping 432 matching lines @@
     if (x == 0) return y;
     if (y == 0) return x;
     if ((x == 1) || (y == 1)) return 1;
     if (y is _Bigint) {
       return x._toBigint().gcd(y);
     }
     return _binaryGcd(x, y, false);
   }
 }
 
-class _Smi extends _IntegerImplementation implements int {
+class _Smi extends _IntegerImplementation implements int, _int64 {
   factory _Smi._uninstantiable() {
     throw new UnsupportedError("_Smi can only be allocated by the VM");
   }
   int get hashCode => this;
   int get _identityHashCode => this;
   int operator ~() native "Smi_bitNegate";
   int get bitLength native "Smi_bitLength";
 
   int operator &(int other) => other._bitAndFromSmi(this);
 
@@ skipping 179 matching lines @@
       // No remainder necessary for this case.
       int digitIndex = -negSmi * 2;
       result._setAt(index, _digitTable[digitIndex + 1]);
       result._setAt(index - 1, _digitTable[digitIndex]);
     }
     return result;
   }
 }
 
 // Represents integers that cannot be represented by Smi but fit into 64bits.
-class _Mint extends _IntegerImplementation implements int {
+class _Mint extends _IntegerImplementation implements int, _int64 {
   factory _Mint._uninstantiable() {
     throw new UnsupportedError("_Mint can only be allocated by the VM");
   }
   int get hashCode => this;
   int get _identityHashCode => this;
   int operator ~() native "Mint_bitNegate";
   int get bitLength native "Mint_bitLength";
 
   int _bitAndFromSmi(int other) => _bitAndFromInteger(other);
 
   // Shift by mint exceeds range that can be handled by the VM.
   int _shrFromInt(int other) {
     if (other < 0) {
       return -1;
     } else {
       return 0;
     }
   }
 
   int _shlFromInt(int other) native "Mint_shlFromInt";
 }