[Bug rtl-optimization/61017] New: lra aborts on optional match_scratch

[amylaar at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=61017

            Bug ID: 61017
           Summary: lra aborts on optional match_scratch
           Product: gcc
           Version: 4.10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: rtl-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: amylaar at gcc dot gnu.org
                CC: vmakarov at gcc dot gnu.org

lra is still not able to compile libgcc2 for ARC:

./cc1 libgcc2.i -O2 -mlra

../../../../unisrc-209293-arc/libgcc/libgcc2.c:2105:1: internal compiler error:
in curr_insn_transform, at lra-constraints.c:3492

The abort happens for the doloop_end_i pattern.
It contains
(clobber (match_scratch:SI 3 "=X,X,&????r"))

and for that, a register is allocated in advance without regard to need:

lra.c:remove_scratches 1992ff
          if (GET_CODE (*id->operand_loc[i]) == SCRATCH
              && GET_MODE (*id->operand_loc[i]) != VOIDmode)
            {
              insn_changed_p = true;
              *id->operand_loc[i] = reg
                = lra_create_new_reg (static_id->operand[i].mode,
                                      *id->operand_loc[i], ALL_REGS, NULL);

As process_alr_operands find that no the alternative uses "X" for that operand,
it set this alternative to NO_REGS:

lra-constraints.c:process_alt_operands 1608ff
          if (curr_static_id->operand_alternative[opalt_num].anything_ok)
            {
              /* Fast track for no constraints at all.  */
              curr_alt[nop] = NO_REGS;
              CLEAR_HARD_REG_SET (curr_alt_set[nop]);
              curr_alt_win[nop] = true;
              curr_alt_match_win[nop] = false;
              curr_alt_offmemok[nop] = false;
              curr_alt_matches[nop] = -1;
              continue;
            }

which causes an abort later:

lra-constraints.c:curr_insn_transform 3486ff
        if (REG_P (reg) && (regno = REGNO (reg)) >= FIRST_PSEUDO_REGISTER)
          {
            bool ok_p = in_class_p (reg, goal_alt[i], &new_class);

            if (new_class != NO_REGS && get_reg_class (regno) != new_class)
              {
                lra_assert (ok_p);
                lra_change_class (regno, new_class, "      Change to", true);
              }
          }