MIPS: Changed "marked" nops to use sll(zero_reg, at, type).

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 645 matching lines @@
     DEBUG_BREAK_NOP,
     // IC markers.
     PROPERTY_ACCESS_INLINED,
     PROPERTY_ACCESS_INLINED_CONTEXT,
     PROPERTY_ACCESS_INLINED_CONTEXT_DONT_DELETE,
     // Helper values.
     LAST_CODE_MARKER,
     FIRST_IC_MARKER = PROPERTY_ACCESS_INLINED
   };
 
-  // Type == 0 is the default non-marking type.
+  // Type == 0 is the default non-marking nop. For mips this is a
+  // sll(zero_reg, zero_reg, 0). We use rt_reg == at for non-zero
+  // marking, to avoid conflict with ssnop and ehb instructions.
   void nop(unsigned int type = 0) {
     ASSERT(type < 32);
-    sll(zero_reg, zero_reg, type, true);
+    Register nop_rt_reg = (type == 0) ? zero_reg : at;
+    sll(zero_reg, nop_rt_reg, type, true);
   }
 
 
   // --------Branch-and-jump-instructions----------
   // We don't use likely variant of instructions.
   void b(int16_t offset);
   void b(Label* L) { b(branch_offset(L, false)>>2); }
   void bal(int16_t offset);
   void bal(Label* L) { bal(branch_offset(L, false)>>2); }
 
@@ skipping 602 matching lines @@
 class EnsureSpace BASE_EMBEDDED {
  public:
   explicit EnsureSpace(Assembler* assembler) {
     assembler->CheckBuffer();
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_ARM_ASSEMBLER_MIPS_H_