A64: Let the Simulator trap BLR XZR instructions.

src/a64/simulator-a64.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 968 matching lines @@
     set_pc(instr->ImmPCOffsetTarget());
   }
 }
 
 
 void Simulator::VisitUnconditionalBranchToRegister(Instruction* instr) {
   Instruction* target = reg<Instruction*>(instr->Rn());
   switch (instr->Mask(UnconditionalBranchToRegisterMask)) {
     case BLR: {
       set_lr(instr->NextInstruction());
+      if (instr->Rn() == 31) {
+        // BLR XZR is used as a guard for the constant pool. We should never hit
+        // this, but if we do trap to allow debugging.
+        Debug();
+      }
       // Fall through.
     }
     case BR:
     case RET: set_pc(target); break;
     default: UNIMPLEMENTED();
   }
 }
 
 
 void Simulator::VisitTestBranch(Instruction* instr) {
@@ skipping 2401 matching lines @@
     default:
       UNIMPLEMENTED();
   }
 }
 
 #endif  // USE_SIMULATOR
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_A64