Fix quadratic test in debug-mode ARM64 assembler

src/arm64/assembler-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
@@ skipping 585 matching lines @@
   DCHECK(m >= 4 && base::bits::IsPowerOfTwo32(m));
   while ((pc_offset() & (m - 1)) != 0) {
     nop();
   }
 }
 
 
 void Assembler::CheckLabelLinkChain(Label const * label) {
 #ifdef DEBUG
   if (label->is_linked()) {
+    static const int kMaxLinksToCheck = 256;  // Avoid O(n2) behaviour.
+    int links_checked = 0;
     int linkoffset = label->pos();
     bool end_of_chain = false;
     while (!end_of_chain) {
+      if (++links_checked > kMaxLinksToCheck) break;
       Instruction * link = InstructionAt(linkoffset);
       int linkpcoffset = link->ImmPCOffset();
       int prevlinkoffset = linkoffset + linkpcoffset;
 
       end_of_chain = (linkoffset == prevlinkoffset);
       linkoffset = linkoffset + linkpcoffset;
     }
   }
 #endif
 }
@@ skipping 2510 matching lines @@
   movz(scratch, (target_offset >> 16) & 0xFFFF, 16);
   movk(scratch, (target_offset >> 32) & 0xFFFF, 32);
   DCHECK((target_offset >> 48) == 0);
   add(rd, rd, scratch);
 }
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_ARM64