MIPS64: Improve long branches utilizing code range.

src/mips64/assembler-mips64.h

 // Copyright (c) 1994-2006 Sun Microsystems Inc.
 // 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.
 //
@@ skipping 506 matching lines @@
     set_target_address_at(pc, constant_pool, target, icache_flush_mode);
   }
 
   // Return the code target address at a call site from the return address
   // of that call in the instruction stream.
   inline static Address target_address_from_return_address(Address pc);
 
   // Return the code target address of the patch debug break slot
   inline static Address break_address_from_return_address(Address pc);
 
+  static void JumpLabelToJumpRegister(Address pc);
+
   static void QuietNaN(HeapObject* nan);
 
   // This sets the branch destination (which gets loaded at the call address).
   // This is for calls and branches within generated code.  The serializer
   // has already deserialized the lui/ori instructions etc.
   inline static void deserialization_set_special_target_at(
       Address instruction_payload, Code* code, Address target) {
     set_target_address_at(
         instruction_payload - kInstructionsFor64BitConstant * kInstrSize,
         code,
@@ skipping 894 matching lines @@
 
    private:
     int start_;
     int end_;
     int next_slot_;
     int free_slot_count_;
   };
 
   int32_t get_trampoline_entry(int32_t pos);
   int unbound_labels_count_;
-  // If trampoline is emitted, generated code is becoming large. As this is
-  // already a slow case which can possibly break our code generation for the
-  // extreme case, we use this information to trigger different mode of
+  // After trampoline is emitted, long branches are used in generated code for
+  // the forward branches whose target offsets could be beyond reach of branch
+  // instruction. We use this information to trigger different mode of
   // branch instruction generation, where we use jump instructions rather
   // than regular branch instructions.
   bool trampoline_emitted_;
-  static const int kTrampolineSlotsSize = 6 * kInstrSize;
+  static const int kTrampolineSlotsSize = 2 * kInstrSize;
   static const int kMaxBranchOffset = (1 << (18 - 1)) - 1;
   static const int kInvalidSlotPos = -1;
 
   // Internal reference positions, required for unbounded internal reference
   // labels.
   std::set<int64_t> internal_reference_positions_;
 
   Trampoline trampoline_;
   bool internal_trampoline_exception_;
 
@@ skipping 11 matching lines @@
 class EnsureSpace BASE_EMBEDDED {
  public:
   explicit EnsureSpace(Assembler* assembler) {
     assembler->CheckBuffer();
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_ARM_ASSEMBLER_MIPS_H_