Re: PR #5753

[Peter Barada <pbarada at mail dot wm dot sps dot mot dot com>]

I've reported a PR (see #5753) while compiling some code from a
m68k-elf configured 3.0.4 compiler for -m5200.  I'm attempting to
figure out a fix.

The compiler reports:

m68k-elf-gcc -fno-exceptions -S -gstabs -malign-int -Wall -Wno-format -m5200 /tmp/cfprintf4.c -o /tmp/cfprintf4.s -da
/tmp/cfprintf4.c: In function `_vformat':
/tmp/cfprintf4.c:58: Insn does not satisfy its constraints:

(insn 258 38 185 (set (reg:QI 8 %a0)
        (mem/f:QI (plus:SI (reg/f:SI 14 %a6)
                (const_int -1 [0xffffffff])) 0)) 37 {*m68k.md:1060} (nil)
    (nil))
/tmp/cfprintf4.c:58: Internal compiler error in final_scan_insn, at final.c:2876

Which indicates that it is trying to load a QImode from memory and
into an address register which the 68k architecture allows, but the
ColdFire architecture rejects.

I've tried to modify HARD_REGNO_MODE_OK to be:

/* Value is 1 if hard register REGNO can hold a value of machine-mode MODE.
   On the 68000, the cpu registers can hold any mode but the 68881 registers
   can hold only SFmode or DFmode.  On ColdFire, no instruction exists
   to move bytes into or out of the address registers. */

#define HARD_REGNO_MODE_OK(REGNO, MODE) 				\
  ((TARGET_5200 && ((REGNO) >= 8 && (REGNO) < 16)			\
    && GET_MODE_SIZE (MODE) == 1) ? 0 :					\
  (((REGNO) < 16							\
    && !((REGNO) < 8 && (REGNO) + GET_MODE_SIZE (MODE) / 4 > 8))	\
   || ((REGNO) >= 16 && (REGNO) < 24				        \
       && (GET_MODE_CLASS (MODE) == MODE_FLOAT				\
	   || GET_MODE_CLASS (MODE) == MODE_COMPLEX_FLOAT)		\
       && GET_MODE_UNIT_SIZE (MODE) <= 12)))

This rejects placing bytes into address registers, and I can successfully
build a compiler, but when I try this code again I get:

/tmp/crap-304-new/bin/m68k-elf-gcc -c -gstabs   -malign-int -m5200 /tmp/cfprintf4.c -o /tmp/cfprintf4.o
/tmp/cfprintf4.c: In function `_vformat':
/tmp/cfprintf4.c:58: Unable to find a register to spill in class `ADDR_REGS'.
/tmp/cfprintf4.c:58: This is the insn:
(insn 185 184 186 (set (reg:SI 68)
        (plus:SI (subreg:SI (mem/f:QI (plus:SI (reg/f:SI 14 %a6)
                        (const_int -1 [0xffffffff])) 0) 0)
            (const_int -100 [0xffffff9c]))) 100 {*addsi3_5200} (nil)
    (nil))
/tmp/cfprintf4.c:58: confused by earlier errors, bailing out

1)  Is limiting HARD_REGNO_MODE_OK() correct in this case?

While debugging this, I find its failing because find_reg is returning
a zero.  At the start of the second loop in find_reg (the one that tests each
of the bits in not_usable), the values of the various bitstrings is:

Breakpoint 8, find_reg (chain=0x82dd164, order=1)
    at /home/pbarada/work/cvs-wavemark/cross-linux-tools/gcc-304/gcc/reload1.c:1701
(gdb) p/x bad_spill_regs
$20 = 0xffc000
(gdb) p/x bad_spill_regs_global
$21 = 0x4000
(gdb) p/x reg_class_contents[rl->class]
$22 = 0xff00
(gdb) p rl->class
$23 = ADDR_REGS
(gdb) p/x not_usable
$24 = 0xffffc0ff
(gdb) p rl->mode
$25 = QImode
(gdb) p/x used_by_other_reload 
$26 = 0x0

And it fails since the only registers available int not_usable are the
address registers a0 through a5(zero bits 8..13).  Apparently all the
data registers are taken due to the inverse of reg_class_contents.
Now the next question is why is the class ADDR_REGS while the mode is
QImode? 

2) How can rl->mode be QImode while the class is ADDR_REGS.

3) Any ideas where I should look from here?

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