Bogus position independent code(PIC) emitted for ColdFire v4e

[Peter Barada]

>Unfortunately ColdFire v4e can't handle the addressing mode of the
>instruction at 0x80000108 since that requires a 32 bit offset.
>I need to modify the compiler to generate PIC code for that
>instruction to look like:
>
>	 move.l  #0x18,%r
>	 move.l  (%a5,%r),%a0
>
>where '%r' is a temporary register.  I've started looking at
>legitimize_pic_address, (gcc/config/m68k/m68k.c) and my eyes starte to
>glaze over.  The leading comment indicates that the "compiler loads
>the address of foo into a register".  Is this legitimize_pic_address,
>or somewhere else that does this (say movsi)?

I started looking at brute-forcing a change in legitimize_pic_address...

I've modified the symbol/label clause of legitimize_pic_address to
look like:

  /* First handle a simple SYMBOL_REF or LABEL_REF */
  if (GET_CODE (orig) == SYMBOL_REF || GET_CODE (orig) == LABEL_REF)
    {
      if (reg == 0)
	abort ();

      if (TARGET_COLDFIRE)
        {
          /* Get the symbol into the register */
          emit_insn (gen_rtx_SET (Pmode, reg, orig));
          /* Now add the pic_offset_table_rtx to it and load indirect */
          pic_ref = gen_rtx_MEM (Pmode,
                                 gen_rtx_PLUS (Pmode,
                                               pic_offset_table_rtx, reg));
        }
      else
        {
          pic_ref = gen_rtx_MEM (Pmode,
                                 gen_rtx_PLUS (Pmode,
                                               pic_offset_table_rtx, orig));
        }
      current_function_uses_pic_offset_table = 1;
      RTX_UNCHANGING_P (pic_ref) = 1;
      emit_move_insn (reg, pic_ref);
      return reg;
    }

Which generates the two pieces of rtl for hte ColdFire case:

;; Start of basic block 0, registers live: 13 [%a5] 14 [%a6] 15 [%sp]
(note 23 5 8 [bb 0] NOTE_INSN_BASIC_BLOCK)

(insn 8 23 10 (set:SI (reg/f:SI 30)
        (symbol_ref/i:SI ("__gmon_start__"))) -1 (nil)
    (expr_list:REG_EQUAL (symbol_ref/i:SI ("__gmon_start__"))
        (nil)))

(insn 10 8 14 (set (reg/f:SI 30)
        (mem/u:SI (plus:SI (reg:SI 13 %a5)
                (reg/f:SI 30)) [0 S4 A8])) 30 {*m68k.md:993} (insn_list 8 (nil))
    (nil))

(insn 14 10 15 (set (cc0)
        (reg/f:SI 30)) 3 {*m68k.md:353} (insn_list 10 (nil))
    (nil))


But unfortunately the compine pass puts it back together again:

;; Start of basic block 0, registers live: 13 [%a5] 14 [%a6] 15 [%sp]
(note 23 5 8 [bb 0] NOTE_INSN_BASIC_BLOCK)

(note 8 23 10 NOTE_INSN_DELETED)

(insn 10 8 14 (set (reg/f:SI 30)
        (mem/u:SI (plus:SI (reg:SI 13 %a5)
                (symbol_ref/i:SI ("__gmon_start__"))) [0 S4 A8])) 30 {*m68k.md:993} (nil)
    (nil))

(insn 14 10 15 (set (cc0)
        (reg/f:SI 30)) 3 {*m68k.md:353} (insn_list 10 (nil))
    (nil))



This is valid for 68020 since an SImode can be part of the offset, but
its illegal for ColdFire. In INDIRECTABLE_1_ADDRESS_P I find:

   || (GET_CODE (X) == PLUS && XEXP (X, 0) == pic_offset_table_rtx 	\
       && flag_pic && GET_CODE (XEXP (X, 1)) == SYMBOL_REF)		\
   || (GET_CODE (X) == PLUS && XEXP (X, 0) == pic_offset_table_rtx 	\
       && flag_pic && GET_CODE (XEXP (X, 1)) == LABEL_REF))

1) Should that have been:

   || (GET_CODE (X) == PLUS && XEXP (X, 0) == pic_offset_table_rtx 	\
       && flag_pic && GET_CODE (XEXP (X, 1)) == SYMBOL_REF)		\
   || (GET_CODE (X) == PLUS && XEXP (X, 1) == pic_offset_table_rtx 	\
       && flag_pic && GET_CODE (XEXP (X, 0)) == LABEL_REF))

2) Should this be changed to:

   || (!TARGET_COLDFIRE &&						\
      (GET_CODE (X) == PLUS && XEXP (X, 0) == pic_offset_table_rtx 	\
       && flag_pic && GET_CODE (XEXP (X, 1)) == SYMBOL_REF)		\
   || (GET_CODE (X) == PLUS && XEXP (X, 0) == pic_offset_table_rtx 	\
       && flag_pic && GET_CODE (XEXP (X, 1)) == LABEL_REF))

To force an addition of a symbol ref and the PIC register to be
rejected, or am I overlooking something...

-- 
Peter Barada                                   Peter.Barada@motorola.com
Wizard                                         781-852-2768 (direct)
WaveMark Solutions(wholly owned by Motorola)   781-270-0193 (fax)