[Bug middle-end/70561] New: Crash in recog_for_combine_1

["vogt at linux dot vnet.ibm.com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70561

            Bug ID: 70561
           Summary: Crash in recog_for_combine_1
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vogt at linux dot vnet.ibm.com
                CC: krebbel at gcc dot gnu.org
  Target Milestone: ---
              Host: s390x
            Target: s390x

This code in recog_for_combine_1 doesn't look right:

--
  if (num_clobbers_to_add)
    {
      rtx newpat = gen_rtx_PARALLEL (VOIDmode,
                                     rtvec_alloc (GET_CODE (pat) == PARALLEL
                                                  ? (XVECLEN (pat, 0)
                                                     + num_clobbers_to_add)
                                                  : num_clobbers_to_add + 1));

      if (GET_CODE (pat) == PARALLEL)
        for (i = 0; i < XVECLEN (pat, 0); i++)
          XVECEXP (newpat, 0, i) = XVECEXP (pat, 0, i);
      else
        XVECEXP (newpat, 0, 0) = pat;

      add_clobbers (newpat, insn_code_number);

      for (i = XVECLEN (newpat, 0) - num_clobbers_to_add;
           i < XVECLEN (newpat, 0); i++)
        {
          if (REG_P (XEXP (XVECEXP (newpat, 0, i), 0))  <=============== crash
              && ! reg_dead_at_p (XEXP (XVECEXP (newpat, 0, i), 0), insn))
            return -1;
          ...
--

For me, there is a crash in the marked line (for some pattern I'm working on)
with "i == 1" because "XVECEXP (newpat, 0, 1)" is "(nil)".  If
"num_clobbers_to_add" is > 0, and the original "pat" is not a parallel, only
the first element of newpat is initialised, but the remaining elements are
still accessed.  There probably should be something like this in the for loop?

  for (...)
    {
      if (XVECEXP (newpat, 0, i))
        /* generate clobber from scratch and store it in XVECEXP (newpat, 0, i)
*/

--

Probably triggered by this splitter:

  [(parallel
    [(set (match_operand:GPR 0 "nonimmediate_operand" "")
          (and:GPR (not:GPR (match_operand:GPR 1 "nonimmediate_operand" ""))
                   (match_operand:GPR 2 "nonimmediate_operand" "")))
    (clobber (reg:CC CC_REGNUM))])]

==>

  [
  (parallel
   [(set (match_dup 3) (and:GPR (match_dup 1) (match_dup 2)))
   (clobber (reg:CC CC_REGNUM))])
  (parallel
   [(set (match_dup 0) (xor:GPR (match_dup 3) (match_dup 2)))
   (clobber (reg:CC CC_REGNUM))])]