Process two 32-bit digits as one 64-bit digit in all bigint intrinsics on ARM64.

runtime/vm/constants_arm64.h

 // Copyright (c) 2014, 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_CONSTANTS_ARM64_H_
 #define VM_CONSTANTS_ARM64_H_
 
 #include "platform/assert.h"
 
 namespace dart {
@@ skipping 437 matching lines @@
   ASRV = MiscDP2SourceFixed | B13 | B11,
 };
 
 // C3.5.9
 enum MiscDP3SourceOp {
   MiscDP3SourceMask = 0x1f000000,
   MiscDP3SourceFixed = DPRegisterFixed | B28 | B24,
   MADD = MiscDP3SourceFixed,
   MSUB = MiscDP3SourceFixed | B15,
   SMULH = MiscDP3SourceFixed | B31 | B22,
+  UMULH = MiscDP3SourceFixed | B31 | B23 | B22,
   UMADDL = MiscDP3SourceFixed | B31 | B23 | B21,
 };
 
 // C3.5.10
 enum LogicalShiftOp {
   LogicalShiftMask = 0x1f000000,
   LogicalShiftFixed = DPRegisterFixed,
   AND = LogicalShiftFixed,
   BIC = LogicalShiftFixed | B21,
   ORR = LogicalShiftFixed | B29,
@@ skipping 590 matching lines @@
   static Instr* At(uword pc) { return reinterpret_cast<Instr*>(pc); }
 
  private:
   DISALLOW_ALLOCATION();
   DISALLOW_IMPLICIT_CONSTRUCTORS(Instr);
 };
 
 }  // namespace dart
 
 #endif  // VM_CONSTANTS_ARM64_H_