Don't touch x18 on ARM64 - it is globally reserved on iOS.

runtime/vm/disassembler_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 "vm/disassembler.h"
 
 #include "vm/globals.h"  // Needed here to get TARGET_ARCH_ARM64.
 #if defined(TARGET_ARCH_ARM64)
 #include "platform/assert.h"
 
@@ skipping 65 matching lines @@
   char cur = *str++;
   while (cur != '\0' && (buffer_pos_ < (buffer_size_ - 1))) {
     buffer_[buffer_pos_++] = cur;
     cur = *str++;
   }
   buffer_[buffer_pos_] = '\0';
 }
 
 
 // These register names are defined in a way to match the native disassembler
-// formatting, except for register aliases ctx (r9) and pp (r10).
+// formatting, except for register aliases ctx (r9), pp (r10) and sp (r19).
 // See for example the command "objdump -d <binary file>".
 static const char* reg_names[kNumberOfCpuRegisters] = {
   "r0",  "r1",  "r2",  "r3",  "r4",  "r5",  "r6",  "r7",
   "r8",  "r9",  "r10", "r11", "r12", "r13", "r14", "r15",
-  "ip0", "ip1", "sp", "r19", "r20", "r21", "r22", "r23",
+  "ip0", "ip1", "r18", "sp",  "r20", "r21", "r22", "r23",
   "r24", "r25", "r26", "pp",  "ctx", "fp",  "lr",  "r31",
 };
 
 
 // Print the register name according to the active name converter.
 void ARM64Decoder::PrintRegister(int reg, R31Type r31t) {
   ASSERT(0 <= reg);
   ASSERT(reg < kNumberOfCpuRegisters);
   if (reg == 31) {
     const char* rstr = (r31t == R31IsZR) ? "zr" : "csp";
@@ skipping 1359 matching lines @@
   int32_t instruction_bits = Instr::At(pc)->InstructionBits();
   OS::SNPrint(hex_buffer, hex_size, "%08x", instruction_bits);
   if (out_instr_size) {
     *out_instr_size = Instr::kInstrSize;
   }
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_ARM