x86,exec,logic: fix shld/shrd with shift bit = 0

* if it is the case, should not perform the shift
* also note that shifting 32 bit on a 32-bit value is UB

src/isa/x86/exec/logic.h

@@ -95,6 +95,8 @@ static inline make_EHelper(not) {
 }
 
 static inline make_EHelper(shld) {
+  rtl_andi(s, dsrc1, dsrc1, 31);
+  if (*dsrc1 != 0) {
     rtl_shl(s, s0, ddest, dsrc1);
 
     rtl_li(s, s1, 32);
@@ -106,11 +108,13 @@ static inline make_EHelper(shld) {
     operand_write(s, id_dest, s0);
     rtl_update_ZFSF(s, s0, id_dest->width);
     // unnecessary to update CF and OF in NEMU
-  //difftest_skip_eflags(EFLAGS_MASK_CF | EFLAGS_MASK_OF);
+  }
   print_asm_template3(shld);
 }
 
 static inline make_EHelper(shrd) {
+  rtl_andi(s, dsrc1, dsrc1, 31);
+  if (*dsrc1 != 0) {
     rtl_shr(s, s0, ddest, dsrc1);
 
     rtl_li(s, s1, 32);
@@ -122,6 +126,6 @@ static inline make_EHelper(shrd) {
     operand_write(s, id_dest, s0);
     rtl_update_ZFSF(s, s0, id_dest->width);
     // unnecessary to update CF and OF in NEMU
-  //difftest_skip_eflags(EFLAGS_MASK_CF | EFLAGS_MASK_OF);
+  }
   print_asm_template3(shrd);
 }