Possible bug in regrename.c???

[Marty Hauff]

I'm still new to GCC but I stumbled across the following anomoly whilst trying to make a new port.

The following RTX:
(set  (mem:HI  (reg/v/f:HI 8 r8 [44]) [8 S2 A8])
     (mem:HI  (pre_dec:HI  (mem:HI  (plus:HI  (reg/f:HI 28 r28)
                     (const_int 3 [0x3])) [17 S2 A8])) [8 S2 A8]))

causes set_value_regno() to segfault.

The following stack trace was observed:
__libc_start_main
main
toplev_main
do_compile
compile_file
c_common_parse_file
yyparse
finish_function
c_expand_body
rest_of_compilation
copyprop_hardreg_forward
copyprop_hardreg_forward_1
for_each_rtx
for_each_rtx
for_each_rtx
kill_autoinc_value
set_value_regno

...and the key routine seems to be...

static int
kill_autoinc_value (px, data)
     rtx *px;
     void *data;
{
  rtx x = *px;
  struct value_data *vd = data;

  if (GET_RTX_CLASS (GET_CODE (x)) == 'a')
    {
      x = XEXP (x, 0);
      kill_value (x, vd);
      set_value_regno (REGNO (x), Pmode, vd);
      return -1;
    }
  return 0;
}

It seems that once in kill_autoinc_value(px, data), if px is looking at the 'pre_dec' rtx, then the "if (GET_RTX_CLASS (GET_CODE (x)) == 'a')" test succeeds.  From what I can work out, the code is expecting the next expression in the sequence to only ever be a REG. Since my RTX contains a MEM expression after the PRE_DEC expression, the REGNO(x) macro returns an absurdly large 'register' number and causes vd->e[regno].mode = mode in set_value_regno() to try to reference a value outside the array.  A segfault results.

My first question is "Is the original RTX valid?" and if so "is this a bug?".  I've thought about putting a "if (REG_P(x))" test around set_value_regno() but I'm not sure if this is the answer and what its implications might be.  I'm hoping someone else might have some suggestions.

Thanks
Marty Moose