MIPS: Refine 'r6 compact branch optimization.'

src/mips/assembler-mips.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 1188 matching lines @@
 
   void EndBlockGrowBuffer() {
     DCHECK(block_buffer_growth_);
     block_buffer_growth_ = false;
   }
 
   bool is_buffer_growth_blocked() const {
     return block_buffer_growth_;
   }
 
+  void EmitForbiddenSlotInstruction() {
+    if (IsPrevInstrCompactBranch()) {
+      nop();
+    }
+  }
+
   inline void CheckTrampolinePoolQuick(int extra_instructions = 0);
 
  private:
   inline static void set_target_internal_reference_encoded_at(Address pc,
                                                               Address target);
 
   // Buffer size and constant pool distance are checked together at regular
   // intervals of kBufferCheckInterval emitted bytes.
   static const int kBufferCheckInterval = 1*KB/2;
 
@@ skipping 213 matching lines @@
  public:
   explicit EnsureSpace(Assembler* assembler) {
     assembler->CheckBuffer();
   }
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_ARM_ASSEMBLER_MIPS_H_