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

@@ -95,33 +95,37 @@ static inline make_EHelper(not) {
 }
 
 static inline make_EHelper(shld) {
-  rtl_shl(s, s0, ddest, dsrc1);
+  rtl_andi(s, dsrc1, dsrc1, 31);
+  if (*dsrc1 != 0) {
+    rtl_shl(s, s0, ddest, dsrc1);
 
-  rtl_li(s, s1, 32);
-  rtl_sub(s, s1, s1, dsrc1);
-  rtl_shr(s, s1, dsrc2, s1);
+    rtl_li(s, s1, 32);
+    rtl_sub(s, s1, s1, dsrc1);
+    rtl_shr(s, s1, dsrc2, s1);
 
-  rtl_or(s, s0, s0, s1);
+    rtl_or(s, s0, s0, s1);
 
-  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);
+    operand_write(s, id_dest, s0);
+    rtl_update_ZFSF(s, s0, id_dest->width);
+    // unnecessary to update CF and OF in NEMU
+  }
   print_asm_template3(shld);
 }
 
 static inline make_EHelper(shrd) {
-  rtl_shr(s, s0, ddest, dsrc1);
+  rtl_andi(s, dsrc1, dsrc1, 31);
+  if (*dsrc1 != 0) {
+    rtl_shr(s, s0, ddest, dsrc1);
 
-  rtl_li(s, s1, 32);
-  rtl_sub(s, s1, s1, dsrc1);
-  rtl_shl(s, s1, dsrc2, s1);
+    rtl_li(s, s1, 32);
+    rtl_sub(s, s1, s1, dsrc1);
+    rtl_shl(s, s1, dsrc2, s1);
 
-  rtl_or(s, s0, s0, s1);
+    rtl_or(s, s0, s0, s1);
 
-  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);
+    operand_write(s, id_dest, s0);
+    rtl_update_ZFSF(s, s0, id_dest->width);
+    // unnecessary to update CF and OF in NEMU
+  }
   print_asm_template3(shrd);
 }