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

src/mips/assembler-mips.h

Index: src/mips/assembler-mips.h
diff --git a/src/mips/assembler-mips.h b/src/mips/assembler-mips.h
index 71637701785e84f4dddaa95524855f84c4cbfb24..ee4daadf1243c584329aa60376636b034b2521a7 100644
--- a/src/mips/assembler-mips.h
+++ b/src/mips/assembler-mips.h
@@ -663,10 +663,13 @@ class Assembler : public AssemblerBase {
     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);
   }