diff --git a/target-mips/helper.h b/target-mips/helper.h
index 9fb5d74029..eed8bd5972 100644
--- a/target-mips/helper.h
+++ b/target-mips/helper.h
@@ -239,14 +239,14 @@ FOP_PROTO(ngt)
 #undef FOP_PROTO
 
 /* Special functions */
-DEF_HELPER(target_ulong, do_di, (target_ulong t0))
-DEF_HELPER(target_ulong, do_ei, (target_ulong t0))
+DEF_HELPER(target_ulong, do_di, (void))
+DEF_HELPER(target_ulong, do_ei, (void))
 DEF_HELPER(void, do_eret, (void))
 DEF_HELPER(void, do_deret, (void))
-DEF_HELPER(target_ulong, do_rdhwr_cpunum, (target_ulong t0))
-DEF_HELPER(target_ulong, do_rdhwr_synci_step, (target_ulong t0))
-DEF_HELPER(target_ulong, do_rdhwr_cc, (target_ulong t0))
-DEF_HELPER(target_ulong, do_rdhwr_ccres, (target_ulong t0))
+DEF_HELPER(target_ulong, do_rdhwr_cpunum, (void))
+DEF_HELPER(target_ulong, do_rdhwr_synci_step, (void))
+DEF_HELPER(target_ulong, do_rdhwr_cc, (void))
+DEF_HELPER(target_ulong, do_rdhwr_ccres, (void))
 DEF_HELPER(void, do_pmon, (int function))
 DEF_HELPER(void, do_wait, (void))
 
diff --git a/target-mips/op_helper.c b/target-mips/op_helper.c
index fe3bbd4d29..6c1d048b71 100644
--- a/target-mips/op_helper.c
+++ b/target-mips/op_helper.c
@@ -1746,18 +1746,20 @@ void r4k_do_tlbr (void)
 #endif /* !CONFIG_USER_ONLY */
 
 /* Specials */
-target_ulong do_di (target_ulong t0)
+target_ulong do_di (void)
 {
-    t0 = env->CP0_Status;
+    target_ulong t0 = env->CP0_Status;
+
     env->CP0_Status = t0 & ~(1 << CP0St_IE);
     cpu_mips_update_irq(env);
 
     return t0;
 }
 
-target_ulong do_ei (target_ulong t0)
+target_ulong do_ei (void)
 {
-    t0 = env->CP0_Status;
+    target_ulong t0 = env->CP0_Status;
+
     env->CP0_Status = t0 | (1 << CP0St_IE);
     cpu_mips_update_irq(env);
 
@@ -1820,48 +1822,48 @@ void do_deret (void)
     env->CP0_LLAddr = 1;
 }
 
-target_ulong do_rdhwr_cpunum(target_ulong t0)
+target_ulong do_rdhwr_cpunum(void)
 {
     if ((env->hflags & MIPS_HFLAG_CP0) ||
         (env->CP0_HWREna & (1 << 0)))
-        t0 = env->CP0_EBase & 0x3ff;
+        return env->CP0_EBase & 0x3ff;
     else
         do_raise_exception(EXCP_RI);
 
-    return t0;
+    return 0;
 }
 
-target_ulong do_rdhwr_synci_step(target_ulong t0)
+target_ulong do_rdhwr_synci_step(void)
 {
     if ((env->hflags & MIPS_HFLAG_CP0) ||
         (env->CP0_HWREna & (1 << 1)))
-        t0 = env->SYNCI_Step;
+        return env->SYNCI_Step;
     else
         do_raise_exception(EXCP_RI);
 
-    return t0;
+    return 0;
 }
 
-target_ulong do_rdhwr_cc(target_ulong t0)
+target_ulong do_rdhwr_cc(void)
 {
     if ((env->hflags & MIPS_HFLAG_CP0) ||
         (env->CP0_HWREna & (1 << 2)))
-        t0 = env->CP0_Count;
+        return env->CP0_Count;
     else
         do_raise_exception(EXCP_RI);
 
-    return t0;
+    return 0;
 }
 
-target_ulong do_rdhwr_ccres(target_ulong t0)
+target_ulong do_rdhwr_ccres(void)
 {
     if ((env->hflags & MIPS_HFLAG_CP0) ||
         (env->CP0_HWREna & (1 << 3)))
-        t0 = env->CCRes;
+        return env->CCRes;
     else
         do_raise_exception(EXCP_RI);
 
-    return t0;
+    return 0;
 }
 
 /* Bitfield operations. */
diff --git a/target-mips/translate.c b/target-mips/translate.c
index c4d91f0e52..9c97b9c486 100644
--- a/target-mips/translate.c
+++ b/target-mips/translate.c
@@ -7386,19 +7386,19 @@ static void decode_opc (CPUState *env, DisasContext *ctx)
                 switch (rd) {
                 case 0:
                     save_cpu_state(ctx, 1);
-                    tcg_gen_helper_1_1(do_rdhwr_cpunum, t0, t0);
+                    tcg_gen_helper_1_0(do_rdhwr_cpunum, t0);
                     break;
                 case 1:
                     save_cpu_state(ctx, 1);
-                    tcg_gen_helper_1_1(do_rdhwr_synci_step, t0, t0);
+                    tcg_gen_helper_1_0(do_rdhwr_synci_step, t0);
                     break;
                 case 2:
                     save_cpu_state(ctx, 1);
-                    tcg_gen_helper_1_1(do_rdhwr_cc, t0, t0);
+                    tcg_gen_helper_1_0(do_rdhwr_cc, t0);
                     break;
                 case 3:
                     save_cpu_state(ctx, 1);
-                    tcg_gen_helper_1_1(do_rdhwr_ccres, t0, t0);
+                    tcg_gen_helper_1_0(do_rdhwr_ccres, t0);
                     break;
                 case 29:
 #if defined (CONFIG_USER_ONLY)
@@ -7548,14 +7548,14 @@ static void decode_opc (CPUState *env, DisasContext *ctx)
                 case OPC_DI:
                     check_insn(env, ctx, ISA_MIPS32R2);
                     save_cpu_state(ctx, 1);
-                    tcg_gen_helper_1_1(do_di, t0, t0);
+                    tcg_gen_helper_1_0(do_di, t0);
                     /* Stop translation as we may have switched the execution mode */
                     ctx->bstate = BS_STOP;
                     break;
                 case OPC_EI:
                     check_insn(env, ctx, ISA_MIPS32R2);
                     save_cpu_state(ctx, 1);
-                    tcg_gen_helper_1_1(do_ei, t0, t0);
+                    tcg_gen_helper_1_0(do_ei, t0);
                     /* Stop translation as we may have switched the execution mode */
                     ctx->bstate = BS_STOP;
                     break;