[Bug target/95443] New: cmpstrnqi patterns update string length

[hjl.tools at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95443

            Bug ID: 95443
           Summary: cmpstrnqi patterns update string length
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: hjl.tools at gmail dot com
                CC: crazylht at gmail dot com, hubicka at ucw dot cz, ubizjak at gmail dot com
  Target Milestone: ---
            Target: i386,x86-64

We have

 countreg = ix86_zero_extend_to_Pmode (operands[3]);

  /* %%% Iff we are testing strict equality, we can use known alignment
     to good advantage.  This may be possible with combine, particularly
     once cc0 is dead.  */
  align = operands[4]; 

  if (CONST_INT_P (operands[3]))
    {
      if (operands[3] == const0_rtx)
        {   
          emit_move_insn (operands[0], const0_rtx);
          DONE;
        }
      emit_insn (gen_cmpstrnqi_nz_1 (addr1, addr2, countreg, align,
                                     operands[1], operands[2]));
    }
  else    
    {
      emit_insn (gen_cmp_1 (Pmode, countreg, countreg));
      emit_insn (gen_cmpstrnqi_1 (addr1, addr2, countreg, align,
                                  operands[1], operands[2]));
    }

cmpstrnqi patterns updates countreg to 0, wich can lead to wrong codes.