MSan workaround in Simulator::VisitBitfield.

src/arm64/simulator-arm64.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 2090 matching lines @@
       break;
     default:
       UNIMPLEMENTED();
   }
 
   int64_t dst = inzero ? 0 : reg(reg_size, instr->Rd());
   int64_t src = reg(reg_size, instr->Rn());
   // Rotate source bitfield into place.
   int64_t result = (static_cast<uint64_t>(src) >> R) | (src << (reg_size - R));
   // Determine the sign extension.
-  int64_t topbits = ((1L << (reg_size - diff - 1)) - 1) << (diff + 1);
-  int64_t signbits = extend && ((src >> S) & 1) ? topbits : 0;
+  int64_t topbits_preshift = (1L << (reg_size - diff - 1)) - 1;
+  int64_t signbits = (extend && ((src >> S) & 1) ? topbits_preshift : 0)
+                     << (diff + 1);
 
   // Merge sign extension, dest/zero and bitfield.
   result = signbits | (result & mask) | (dst & ~mask);
 
   set_reg(reg_size, instr->Rd(), result);
 }
 
 
 void Simulator::VisitExtract(Instruction* instr) {
   unsigned lsb = instr->ImmS();
@@ skipping 1513 matching lines @@
     default:
       UNIMPLEMENTED();
   }
 }
 
 #endif  // USE_SIMULATOR
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM64