ARM64: Avoid iterating through all unresolved branch infos when many are pending.

src/arm64/assembler-arm64.h

 // 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 1676 matching lines @@
   void db(uint8_t data) { dc8(data); }
 
   // Code generation helpers --------------------------------------------------
 
   unsigned num_pending_reloc_info() const { return num_pending_reloc_info_; }
 
   Instruction* InstructionAt(int offset) const {
     return reinterpret_cast<Instruction*>(buffer_ + offset);
   }
 
+  ptrdiff_t InstructionOffset(Instruction* instr) const {
+    return reinterpret_cast<byte*>(instr) - buffer_;
+  }
+
   // Register encoding.
   static Instr Rd(CPURegister rd) {
     ASSERT(rd.code() != kSPRegInternalCode);
     return rd.code() << Rd_offset;
   }
 
   static Instr Rn(CPURegister rn) {
     ASSERT(rn.code() != kSPRegInternalCode);
     return rn.code() << Rn_offset;
   }
@@ skipping 468 matching lines @@
   // It is maintained to the closest unresolved branch limit minus the maximum
   // veneer margin (or kMaxInt if there are no unresolved branches).
   int next_veneer_pool_check_;
 
  private:
   // If a veneer is emitted for a branch instruction, that instruction must be
   // removed from the associated label's link chain so that the assembler does
   // not later attempt (likely unsuccessfully) to patch it to branch directly to
   // the label.
   void DeleteUnresolvedBranchInfoForLabel(Label* label);
+  // This function deletes the information related to the label by iterating
+  // through all unresolved branch infos and deleting the appropriating one. Its
+  // complexity is proportional to the number of unresolved branches pending.
+  void DeleteUnresolvedBranchInfoForLabelIterate(Label* label);
+  // This function deletes the information related to the label by traversing
+  // the label chain, and for each PC-relative instruction in the chain checking
+  // if pending unresolved information exists. Its complexity is proportional to
+  // the length of the label chain.
+  void DeleteUnresolvedBranchInfoForLabelTraverse(Label* label);
 
  private:
   PositionsRecorder positions_recorder_;
   friend class PositionsRecorder;
   friend class EnsureSpace;
 };
 
 class PatchingAssembler : public Assembler {
  public:
   // Create an Assembler with a buffer starting at 'start'.
@@ skipping 43 matching lines @@
 class EnsureSpace BASE_EMBEDDED {
  public:
   explicit EnsureSpace(Assembler* assembler) {
     assembler->CheckBuffer();
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_ARM64_ASSEMBLER_ARM64_H_