diff --git a/src/engine/rv64/isa/x86.c b/src/engine/rv64/isa/x86.c
index ca4dc009826d714003d1ab6b858d09d56ddd4c39..ea64057764672dd759a0428ae986646538635a51 100644
--- a/src/engine/rv64/isa/x86.c
+++ b/src/engine/rv64/isa/x86.c
@@ -1,8 +1,10 @@
+#ifdef __ISA_x86__
+
 #include <cpu/decode.h>
 #include <rtl/rtl.h>
 #include <isa.h>
 
-uint8_t reg_ptr2idx(DecodeExecState *s, const rtlreg_t* dest) {
+uint32_t reg_ptr2idx(DecodeExecState *s, const rtlreg_t* dest) {
   rtlreg_t* gpr_start = (rtlreg_t *)cpu.gpr;
   rtlreg_t* gpr_end = (void *)gpr_start + sizeof(cpu.gpr);
 
@@ -25,3 +27,5 @@ uint8_t reg_ptr2idx(DecodeExecState *s, const rtlreg_t* dest) {
   CASE(&cpu.SF, 1)
   panic("bad ptr = %p", dest);
 }
+
+#endif
diff --git a/src/engine/rv64/rv64-backend/exec.c b/src/engine/rv64/rv64-backend/exec.c
index b51a8a81bb96b9638847699c7f65b14773b29b59..4323dd9c3895b5f676dfdbe8e42cee434c11260f 100644
--- a/src/engine/rv64/rv64-backend/exec.c
+++ b/src/engine/rv64/rv64-backend/exec.c
@@ -40,7 +40,7 @@ vaddr_t rv64_exec_trans_buffer(void *buf, int nr_instr) {
     rv64_getregs(&r);
   }
 
-  return r.gpr[30]._64;
+  return r.gpr[tmp0]._64;
 }
 
 void rv64_guest_getregs(void *cpu) {
@@ -67,7 +67,7 @@ void rv64_guest_setregs(void *cpu) {
 void init_rv64_reg() {
   CPU_state r;
   rv64_getregs(&r);
-  r.gpr[24]._64 = 0x00000000fffffffful;
-  r.gpr[25]._64 = 0x000000000000fffful;
+  r.gpr[mask32]._64 = 0x00000000fffffffful;
+  r.gpr[mask16]._64 = 0x000000000000fffful;
   rv64_setregs(&r);
 }
diff --git a/src/engine/rv64/rv64-backend/relop.c b/src/engine/rv64/rv64-backend/relop.c
index 66f1210758053403545079c968dd98cc6599f64f..59d776d970ef03d513a02d2f768201811b2a9489 100644
--- a/src/engine/rv64/rv64-backend/relop.c
+++ b/src/engine/rv64/rv64-backend/relop.c
@@ -1,18 +1,19 @@
 #include <rtl/rtl.h>
 #include "rv_ins_def.h"
+#include "../tran.h"
 
 void rv64_relop(uint32_t relop, uint32_t idx_dest, uint32_t idx_src1, uint32_t idx_src2) {
   switch (relop) {
     case RELOP_FALSE: rv64_addi(idx_dest, x0, 0); return;
     case RELOP_TRUE:  rv64_addi(idx_dest, x0, 1); return;
     case RELOP_EQ:
-      rv64_xor(x31, idx_src1, idx_src2);
-      rv64_sltu(idx_dest, x0, x31);
+      rv64_xor(idx_dest, idx_src1, idx_src2);
+      rv64_sltu(idx_dest, x0, idx_dest);
       rv64_xori(idx_dest, idx_dest, 1);
       return;
     case RELOP_NE:
-      rv64_xor(x31, idx_src1, idx_src2);
-      rv64_sltu(idx_dest, x0, x31);
+      rv64_xor(idx_dest, idx_src1, idx_src2);
+      rv64_sltu(idx_dest, x0, idx_dest);
       return;
     case RELOP_LT: rv64_slt(idx_dest, idx_src1, idx_src2); return;
     case RELOP_LE:
diff --git a/src/engine/rv64/rv64-backend/rtl-basic.c b/src/engine/rv64/rv64-backend/rtl-basic.c
index 39c919a4a792e8b41509f504fb0393115ccd3a4e..ecf2fa0e001296fe4fe7721d36634358de17d113 100644
--- a/src/engine/rv64/rv64-backend/rtl-basic.c
+++ b/src/engine/rv64/rv64-backend/rtl-basic.c
@@ -3,11 +3,11 @@
 #include "../tran.h"
 
 void rv64_relop(uint32_t relop, uint32_t idx_dest, uint32_t idx_src1, uint32_t idx_src2);
-uint8_t reg_ptr2idx(DecodeExecState *s, const rtlreg_t* dest);
+uint32_t reg_ptr2idx(DecodeExecState *s, const rtlreg_t* dest);
 
-static inline void rv64_zextw(uint8_t rd, uint8_t rs) {
-  // x24 is set during initialization
-  rv64_and(rd, rs, x24);
+static inline void rv64_zextw(uint32_t rd, uint32_t rs) {
+  // mask32 is set during initialization
+  rv64_and(rd, rs, mask32);
 }
 
 // return false if `imm` can be represented within 12 bits
@@ -65,7 +65,7 @@ make_rtl_compute_reg(xor, xor)
 
 make_rtl(addi, rtlreg_t* dest, const rtlreg_t* src1, const sword_t imm) {
   if (src1 == rz) load_imm(reg_ptr2idx(s, dest), imm);
-  else if (load_imm_big(x31, imm)) rv64_addw(reg_ptr2idx(s, dest), reg_ptr2idx(s, src1), x31);
+  else if (load_imm_big(tmp0, imm)) rv64_addw(reg_ptr2idx(s, dest), reg_ptr2idx(s, src1), tmp0);
   else rv64_addiw(reg_ptr2idx(s, dest), reg_ptr2idx(s, src1), imm);
 }
 
@@ -75,19 +75,19 @@ make_rtl(subi, rtlreg_t* dest, const rtlreg_t* src1, const sword_t imm) {
 
 make_rtl(andi, rtlreg_t* dest, const rtlreg_t* src1, const sword_t imm) {
   if (src1 == rz) load_imm(reg_ptr2idx(s, dest), 0);
-  else if (load_imm_big(x31, imm)) rv64_and(reg_ptr2idx(s, dest), reg_ptr2idx(s, src1), x31);
+  else if (load_imm_big(tmp0, imm)) rv64_and(reg_ptr2idx(s, dest), reg_ptr2idx(s, src1), tmp0);
   else rv64_andi(reg_ptr2idx(s, dest), reg_ptr2idx(s, src1), imm);
 }
 
 make_rtl(xori, rtlreg_t* dest, const rtlreg_t* src1, const sword_t imm) {
   if (src1 == rz) load_imm(reg_ptr2idx(s, dest), imm);
-  else if (load_imm_big(x31, imm)) rv64_xor(reg_ptr2idx(s, dest), reg_ptr2idx(s, src1), x31);
+  else if (load_imm_big(tmp0, imm)) rv64_xor(reg_ptr2idx(s, dest), reg_ptr2idx(s, src1), tmp0);
   else rv64_xori(reg_ptr2idx(s, dest), reg_ptr2idx(s, src1), imm);
 }
 
 make_rtl(ori, rtlreg_t* dest, const rtlreg_t* src1, const sword_t imm) {
   if (src1 == rz) load_imm(reg_ptr2idx(s, dest), imm);
-  else if (load_imm_big(x31, imm)) rv64_or(reg_ptr2idx(s, dest), reg_ptr2idx(s, src1), x31);
+  else if (load_imm_big(tmp0, imm)) rv64_or(reg_ptr2idx(s, dest), reg_ptr2idx(s, src1), tmp0);
   else rv64_ori(reg_ptr2idx(s, dest), reg_ptr2idx(s, src1), imm);
 }
 
@@ -116,7 +116,7 @@ make_rtl(setrelop, uint32_t relop, rtlreg_t *dest, const rtlreg_t *src1, const r
 }
 
 make_rtl(setrelopi, uint32_t relop, rtlreg_t *dest, const rtlreg_t *src1, const sword_t imm) {
-  int big_imm = load_imm_big(x31, imm);
+  int big_imm = load_imm_big(tmp0, imm);
   uint32_t idx_dest = reg_ptr2idx(s, dest);
   uint32_t idx_src1 = reg_ptr2idx(s, src1);
   if (!big_imm && (relop == RELOP_LT || relop == RELOP_LTU)) {
@@ -126,8 +126,8 @@ make_rtl(setrelopi, uint32_t relop, rtlreg_t *dest, const rtlreg_t *src1, const
       // fall through for default cases
     }
   }
-  if (!big_imm) rv64_addiw(x31, x0, imm);
-  rv64_relop(relop, idx_dest, idx_src1, x31);
+  if (!big_imm) rv64_addiw(tmp0, x0, imm);
+  rv64_relop(relop, idx_dest, idx_src1, tmp0);
 }
 
 
@@ -145,19 +145,19 @@ make_rtl_compute_reg(idiv_r, remw)
 # define rv64_imul_hi(c, a, b) TODO()
 #else
 make_rtl(mul_hi, rtlreg_t* dest, const rtlreg_t* src1, const rtlreg_t* src2) {
-  uint8_t idx_dest = reg_ptr2idx(s, dest);
-  uint8_t idx_src1 = reg_ptr2idx(s, src1);
-  uint8_t idx_src2 = reg_ptr2idx(s, src2);
-  rv64_zextw(x30, idx_src1);
-  rv64_zextw(x31, idx_src2);
-  rv64_mul(idx_dest, x30, x31);
+  uint32_t idx_dest = reg_ptr2idx(s, dest);
+  uint32_t idx_src1 = reg_ptr2idx(s, src1);
+  uint32_t idx_src2 = reg_ptr2idx(s, src2);
+  rv64_zextw(tmp1, idx_src1);
+  rv64_zextw(tmp0, idx_src2);
+  rv64_mul(idx_dest, tmp1, tmp0);
   rv64_srai(idx_dest, idx_dest, 32);
 }
 
 make_rtl(imul_hi, rtlreg_t* dest, const rtlreg_t* src1, const rtlreg_t* src2) {
-  uint8_t idx_dest = reg_ptr2idx(s, dest);
-  uint8_t idx_src1 = reg_ptr2idx(s, src1);
-  uint8_t idx_src2 = reg_ptr2idx(s, src2);
+  uint32_t idx_dest = reg_ptr2idx(s, dest);
+  uint32_t idx_src1 = reg_ptr2idx(s, src1);
+  uint32_t idx_src2 = reg_ptr2idx(s, src2);
   rv64_mul(idx_dest, idx_src1, idx_src2);
   rv64_srai(idx_dest, idx_dest, 32);
 }
@@ -165,109 +165,113 @@ make_rtl(imul_hi, rtlreg_t* dest, const rtlreg_t* src1, const rtlreg_t* src2) {
 
 make_rtl(div64_q, rtlreg_t* dest,
     const rtlreg_t* src1_hi, const rtlreg_t* src1_lo, const rtlreg_t* src2) {
-  uint8_t idx_dest = reg_ptr2idx(s, dest);
-  uint8_t idx_src1_hi = reg_ptr2idx(s, src1_hi);
-  uint8_t idx_src1_lo = reg_ptr2idx(s, src1_lo);
-  uint8_t idx_src2 = reg_ptr2idx(s, src2);
-
-  rv64_slli(x30, idx_src1_hi, 32);
-  rv64_zextw(x31, idx_src1_lo);
-  rv64_or(x30, x30, x31);
-  rv64_zextw(x31, idx_src2);
-  rv64_divu(idx_dest, x30, x31);
+  uint32_t idx_dest = reg_ptr2idx(s, dest);
+  uint32_t idx_src1_hi = reg_ptr2idx(s, src1_hi);
+  uint32_t idx_src1_lo = reg_ptr2idx(s, src1_lo);
+  uint32_t idx_src2 = reg_ptr2idx(s, src2);
+
+  rv64_slli(tmp1, idx_src1_hi, 32);
+  rv64_zextw(tmp0, idx_src1_lo);
+  rv64_or(tmp1, tmp1, tmp0);
+  rv64_zextw(tmp0, idx_src2);
+  rv64_divu(idx_dest, tmp1, tmp0);
 }
 
 make_rtl(div64_r, rtlreg_t* dest,
     const rtlreg_t* src1_hi, const rtlreg_t* src1_lo, const rtlreg_t* src2) {
-  uint8_t idx_dest = reg_ptr2idx(s, dest);
-  uint8_t idx_src1_hi = reg_ptr2idx(s, src1_hi);
-  uint8_t idx_src1_lo = reg_ptr2idx(s, src1_lo);
-  uint8_t idx_src2 = reg_ptr2idx(s, src2);
-
-  rv64_slli(x30, idx_src1_hi, 32);
-  rv64_zextw(x31, idx_src1_lo);
-  rv64_or(x30, x30, x31);
-  rv64_zextw(x31, idx_src2);
-  rv64_remu(idx_dest, x30, x31);
+  uint32_t idx_dest = reg_ptr2idx(s, dest);
+  uint32_t idx_src1_hi = reg_ptr2idx(s, src1_hi);
+  uint32_t idx_src1_lo = reg_ptr2idx(s, src1_lo);
+  uint32_t idx_src2 = reg_ptr2idx(s, src2);
+
+  rv64_slli(tmp1, idx_src1_hi, 32);
+  rv64_zextw(tmp0, idx_src1_lo);
+  rv64_or(tmp1, tmp1, tmp0);
+  rv64_zextw(tmp0, idx_src2);
+  rv64_remu(idx_dest, tmp1, tmp0);
 }
 
 make_rtl(idiv64_q, rtlreg_t* dest,
     const rtlreg_t* src1_hi, const rtlreg_t* src1_lo, const rtlreg_t* src2) {
-  uint8_t idx_dest = reg_ptr2idx(s, dest);
-  uint8_t idx_src1_hi = reg_ptr2idx(s, src1_hi);
-  uint8_t idx_src1_lo = reg_ptr2idx(s, src1_lo);
-  uint8_t idx_src2 = reg_ptr2idx(s, src2);
-
-  rv64_slli(x30, idx_src1_hi, 32);
-  rv64_zextw(x31, idx_src1_lo);
-  rv64_or(x30, x30, x31);
-  rv64_div(idx_dest, x30, idx_src2);
+  uint32_t idx_dest = reg_ptr2idx(s, dest);
+  uint32_t idx_src1_hi = reg_ptr2idx(s, src1_hi);
+  uint32_t idx_src1_lo = reg_ptr2idx(s, src1_lo);
+  uint32_t idx_src2 = reg_ptr2idx(s, src2);
+
+  rv64_slli(tmp1, idx_src1_hi, 32);
+  rv64_zextw(tmp0, idx_src1_lo);
+  rv64_or(tmp1, tmp1, tmp0);
+  rv64_div(idx_dest, tmp1, idx_src2);
 }
 
 make_rtl(idiv64_r, rtlreg_t* dest,
     const rtlreg_t* src1_hi, const rtlreg_t* src1_lo, const rtlreg_t* src2) {
-  uint8_t idx_dest = reg_ptr2idx(s, dest);
-  uint8_t idx_src1_hi = reg_ptr2idx(s, src1_hi);
-  uint8_t idx_src1_lo = reg_ptr2idx(s, src1_lo);
-  uint8_t idx_src2 = reg_ptr2idx(s, src2);
-
-  rv64_slli(x30, idx_src1_hi, 32);
-  rv64_zextw(x31, idx_src1_lo);
-  rv64_or(x30, x30, x31);
-  rv64_rem(idx_dest, x30, idx_src2);
+  uint32_t idx_dest = reg_ptr2idx(s, dest);
+  uint32_t idx_src1_hi = reg_ptr2idx(s, src1_hi);
+  uint32_t idx_src1_lo = reg_ptr2idx(s, src1_lo);
+  uint32_t idx_src2 = reg_ptr2idx(s, src2);
+
+  rv64_slli(tmp1, idx_src1_hi, 32);
+  rv64_zextw(tmp0, idx_src1_lo);
+  rv64_or(tmp1, tmp1, tmp0);
+  rv64_rem(idx_dest, tmp1, idx_src2);
 }
 
 make_rtl(lm, rtlreg_t *dest, const rtlreg_t* addr, const sword_t imm, int len) {
-  uint8_t idx_dest = reg_ptr2idx(s, dest);
-  uint8_t idx_addr = reg_ptr2idx(s, addr);
+  uint32_t idx_dest = reg_ptr2idx(s, dest);
+  uint32_t idx_addr = reg_ptr2idx(s, addr);
 
   RV_IMM rv_imm = { .val = imm };
   uint32_t lui_imm = rv_imm.imm_31_12 + (rv_imm.imm_11_0 >> 11);
-  if (addr == rz) rv64_lui(x31, lui_imm);
-  else if (lui_imm == 0) rv64_zextw(x31, idx_addr);
+  if (addr == rz) rv64_lui(tmp0, lui_imm);
+  else if (lui_imm == 0) rv64_zextw(tmp0, idx_addr);
   else {
-    rv64_lui(x31, lui_imm);
-    rv64_add(x31, x31, idx_addr);
-    rv64_zextw(x31, x31);
+    rv64_lui(tmp0, lui_imm);
+    rv64_add(tmp0, tmp0, idx_addr);
+    rv64_zextw(tmp0, tmp0);
   }
 
   switch (len) {
-    case 1: rv64_lbu(idx_dest, x31, imm & 0xfff); break;
-    case 2: rv64_lhu(idx_dest, x31, imm & 0xfff); break;
-    case 4: rv64_lwu(idx_dest, x31, imm & 0xfff); break;
-    case 8: rv64_ld (idx_dest, x31, imm & 0xfff); break;
+    case 1: rv64_lbu(idx_dest, tmp0, imm & 0xfff); break;
+    case 2: rv64_lhu(idx_dest, tmp0, imm & 0xfff); break;
+    case 4: rv64_lwu(idx_dest, tmp0, imm & 0xfff); break;
+    case 8: rv64_ld (idx_dest, tmp0, imm & 0xfff); break;
     default: assert(0);
   }
 }
 
 make_rtl(sm, const rtlreg_t* addr, const sword_t imm, const rtlreg_t* src1, int len) {
-  uint8_t idx_addr = reg_ptr2idx(s, addr);
-  uint8_t idx_src1 = reg_ptr2idx(s, src1);
+  uint32_t idx_addr = reg_ptr2idx(s, addr);
+  uint32_t idx_src1 = reg_ptr2idx(s, src1);
 
   RV_IMM rv_imm = { .val = imm };
   uint32_t lui_imm = rv_imm.imm_31_12 + (rv_imm.imm_11_0 >> 11);
-  if (addr == rz) rv64_lui(x31, lui_imm);
-  else if (lui_imm == 0) rv64_zextw(x31, idx_addr);
+  if (addr == rz) rv64_lui(tmp0, lui_imm);
+  else if (lui_imm == 0) rv64_zextw(tmp0, idx_addr);
   else {
-    rv64_lui(x31, lui_imm);
-    rv64_add(x31, x31, idx_addr);
-    rv64_zextw(x31, x31);
+    rv64_lui(tmp0, lui_imm);
+    rv64_add(tmp0, tmp0, idx_addr);
+    rv64_zextw(tmp0, tmp0);
   }
   switch (len) {
-    case 1: rv64_sb(idx_src1, x31, imm & 0xfff); break;
-    case 2: rv64_sh(idx_src1, x31, imm & 0xfff); break;
-    case 4: rv64_sw(idx_src1, x31, imm & 0xfff); break;
-    case 8: rv64_sd(idx_src1, x31, imm & 0xfff); break;
+    case 1: rv64_sb(idx_src1, tmp0, imm & 0xfff); break;
+    case 2: rv64_sh(idx_src1, tmp0, imm & 0xfff); break;
+    case 4: rv64_sw(idx_src1, tmp0, imm & 0xfff); break;
+    case 8: rv64_sd(idx_src1, tmp0, imm & 0xfff); break;
     default: assert(0);
   }
 }
 
 make_rtl(host_lm, rtlreg_t* dest, const void *addr, int len) {
-  uint8_t idx_dest = reg_ptr2idx(s, dest);
+#ifndef __ISA_x86__
+  panic("should not reach here");
+#endif
+
+  uint32_t idx_dest = reg_ptr2idx(s, dest);
 
   // we assume that `addr` is only from cpu.gpr in x86
   uintptr_t addr_align = (uintptr_t)addr & ~(sizeof(rtlreg_t) - 1);
-  uint8_t idx_r = reg_ptr2idx(s, (void *)addr_align);
+  uint32_t idx_r = reg_ptr2idx(s, (void *)addr_align);
   switch (len) {
     case 1: ;
       int is_high = (uintptr_t)addr & 1;
@@ -279,18 +283,22 @@ make_rtl(host_lm, rtlreg_t* dest, const void *addr, int len) {
       }
       return;
     case 2:
-      rv64_and(idx_dest, idx_r, x25); // x25 is set during initialization
+      rv64_and(idx_dest, idx_r, mask16); // mask16 is set during initialization
       return;
     default: assert(0);
   }
 }
 
 make_rtl(host_sm, void *addr, const rtlreg_t *src1, int len) {
-  uint8_t idx_src1 = reg_ptr2idx(s, src1);
+#ifndef __ISA_x86__
+  panic("should not reach here");
+#endif
+
+  uint32_t idx_src1 = reg_ptr2idx(s, src1);
 
   // we assume that `addr` is only from cpu.gpr in x86
   uintptr_t addr_align = (uintptr_t)addr & ~(sizeof(rtlreg_t) - 1);
-  uint8_t idx_r = reg_ptr2idx(s, (void *)addr_align);
+  uint32_t idx_r = reg_ptr2idx(s, (void *)addr_align);
 
   spm(sw, idx_r, SPM_X86_REG);
   if (len == 1) spm(sb, idx_src1, SPM_X86_REG + ((uintptr_t)addr & 1));
@@ -299,14 +307,14 @@ make_rtl(host_sm, void *addr, const rtlreg_t *src1, int len) {
   spm(lwu, idx_r, SPM_X86_REG);
 }
 
-// we use x30 to store x86.pc of the next basic block
+// we use tmp0 to store x86.pc of the next basic block
 make_rtl(j, vaddr_t target) {
-  if (!load_imm_big(x30, target)) rv64_addiw(x30, x30, target & 0xfff);
+  if (!load_imm_big(tmp0, target)) rv64_addiw(tmp0, tmp0, target & 0xfff);
   tran_next_pc = NEXT_PC_JMP;
 }
 
 make_rtl(jr, rtlreg_t *target) {
-  rv64_addi(x30, reg_ptr2idx(s, target), 0);
+  rv64_addi(tmp0, reg_ptr2idx(s, target), 0);
   tran_next_pc = NEXT_PC_JMP;
 }
 
@@ -336,9 +344,9 @@ make_rtl(jrelop, uint32_t relop, const rtlreg_t *src1, const rtlreg_t *src2, vad
   }
 
   // generate instrutions to load the not-taken target
-  load_imm_no_opt(x30, s->seq_pc);  // only two instructions
+  load_imm_no_opt(tmp0, s->seq_pc);  // only two instructions
   // generate instrutions to load the taken target
-  load_imm_no_opt(x30, target);     // only two instructions
+  load_imm_no_opt(tmp0, target);     // only two instructions
 
   tran_next_pc = NEXT_PC_BRANCH;
 
diff --git a/src/engine/rv64/rv64-backend/rv_ins_def.h b/src/engine/rv64/rv64-backend/rv_ins_def.h
index 77be8b0dcb0e3a0a10dab891ac569cf039d8d2c7..d0e2bd915276b6d5e03bd950a15c6f10bdf3e1ea 100644
--- a/src/engine/rv64/rv64-backend/rv_ins_def.h
+++ b/src/engine/rv64/rv64-backend/rv_ins_def.h
@@ -165,8 +165,6 @@ static inline void gen_rv64_CSR_inst(uint8_t opcode, uint8_t rd,
   write_ins(ins.val);
 }
 
-enum { x0 = 0, x24 = 24, x25, x26, x27, x28, x29, x30, x31 };
-
 // RV64I
 #define rv64_lui(rd, imm)            gen_rv64_U_inst(0b0110111, rd, imm)
 #define rv64_auipc(rd, imm)          gen_rv64_U_inst(0b0010111, rd, imm)
diff --git a/src/engine/rv64/tran.h b/src/engine/rv64/tran.h
index 8b490398dda874507f4eec0f845f167ac2890be2..8cacf05872e1c6de921a477e6681a1fa7a2d6ce3 100644
--- a/src/engine/rv64/tran.h
+++ b/src/engine/rv64/tran.h
@@ -13,4 +13,10 @@ enum { NEXT_PC_SEQ, NEXT_PC_JMP, NEXT_PC_BRANCH };
 #define spm(op, reg, offset) concat(rv64_, op)(reg, x0, offset)
 #define SPM_X86_REG 0    // x86 byte/word register write
 
+enum { x0 = 0 };
+
+#ifdef __ISA_x86__
+enum { tmp0 = 30, tmp1 = 31, mask32 = 24, mask16 = 25 };
+#endif
+
 #endif