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

runtime/vm/simulator_arm64.cc

 // 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.
 
 #include <setjmp.h>
 #include <stdlib.h>
 
 #include "vm/globals.h"
 #if defined(TARGET_ARCH_ARM64)
 
@@ skipping 2512 matching lines @@
     }
   } else if ((instr->Bits(29, 2) == 0) && (instr->Bits(21, 3) == 2) &&
              (instr->Bit(15) == 0)) {
     // Format(instr, "smulh 'rd, 'rn, 'rm");
     const int64_t rn_val = get_register(rn, R31IsZR);
     const int64_t rm_val = get_register(rm, R31IsZR);
     const __int128 res =
         static_cast<__int128>(rn_val) * static_cast<__int128>(rm_val);
     const int64_t alu_out = static_cast<int64_t>(res >> 64);
     set_register(instr, rd, alu_out, R31IsZR);
+  } else if ((instr->Bits(29, 2) == 0) && (instr->Bits(21, 3) == 6) &&
+             (instr->Bit(15) == 0)) {
+    // Format(instr, "umulh 'rd, 'rn, 'rm");
+    const uint64_t rn_val = get_register(rn, R31IsZR);
+    const uint64_t rm_val = get_register(rm, R31IsZR);
+    const __int128 res =
+        static_cast<__int128>(rn_val) * static_cast<__int128>(rm_val);
+    const int64_t alu_out = static_cast<int64_t>(res >> 64);
+    set_register(instr, rd, alu_out, R31IsZR);
   } else if ((instr->Bits(29, 3) == 4) && (instr->Bits(21, 3) == 5) &&
              (instr->Bit(15) == 0)) {
     // Format(instr, "umaddl 'rd, 'rn, 'rm, 'ra");
     const uint64_t rn_val = static_cast<uint32_t>(get_wregister(rn, R31IsZR));
     const uint64_t rm_val = static_cast<uint32_t>(get_wregister(rm, R31IsZR));
     const uint64_t ra_val = get_register(ra, R31IsZR);
     const uint64_t alu_out = ra_val + (rn_val * rm_val);
     set_register(instr, rd, alu_out, R31IsZR);
   } else {
     UnimplementedInstruction(instr);
@@ skipping 942 matching lines @@
   set_register(NULL, kExceptionObjectReg, bit_cast<int64_t>(raw_exception));
   set_register(NULL, kStackTraceObjectReg, bit_cast<int64_t>(raw_stacktrace));
   buf->Longjmp();
 }
 
 }  // namespace dart
 
 #endif  // !defined(HOST_ARCH_ARM64)
 
 #endif  // defined TARGET_ARCH_ARM64