[Bug target/101697] [11/12 regression] ICE compiling uClibc-ng for h8300-linux

["law at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101697

Jeffrey A. Law <law at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |ASSIGNED
           Assignee|unassigned at gcc dot gnu.org      |law at gcc dot gnu.org
   Last reconfirmed|                            |2021-08-17

--- Comment #4 from Jeffrey A. Law <law at gcc dot gnu.org> ---
I've managed to reproduce.  It's possible I was missing the -fno-builtin on my
command line.

A much simplified testcase:
struct gaih_servtuple
{
  struct gaih_servtuple *next;
};


int
gaih_inet (const char *name,  const void *req)
{
  struct gaih_servtuple *st;
  int *tp;
  if (req)
    ++tp;

  struct gaih_servtuple **pst = &st;
  while (1)
    {
      struct gaih_servtuple *newp;


      newp = __builtin_alloca (sizeof (struct gaih_servtuple));
      frob (name, tp, req, newp);
      *pst = newp;
      pst = &(newp->next);
      tp++;
    }
}

We're fine up to and including IRA.
(insn 20 18 22 5 (set (reg/f:SI 28)
        (reg/f:SI 7 sp)) "k.c":21:14 19 {*movsi}
     (nil))
(insn 22 20 23 5 (set (mem/f:SI (pre_dec:SI (reg/f:SI 7 sp)) [1  S4 A32])
        (reg/f:SI 28)) "k.c":22:7 19 {*movsi}
     (expr_list:REG_ARGS_SIZE (const_int 4 [0x4])
        (nil)))

And IRA allocates hard reg #6 for pseudo #28, which is also fine.

Reload reports:
Reload 1: reload_in (SI) = (reg/f:SI 28)
        GENERAL_REGS, RELOAD_FOR_INPUT (opnum = 1)
        reload_in_reg: (reg/f:SI 28)
        reload_reg_rtx: (reg/f:SI 7 sp)

Which is not good as replacing (reg 28) with (reg sp) is not valid.

I haven't tried converting the H8 to LRA yet, which would be the ultimate
solution if it worked.  Ideally any port not converted to LRA ought to be
flagged as deprecated for gcc-12 and dropped if not fixed by gcc-13.