RE: [avr-gcc-list] wrong code from avr-gcc 4.1.2?

[John Regehr]

Hi Eric-

I'm using Kevin Klues' avr-gcc debs for TinyOS.  I expect that he built a 
patched version but I'll check with him to make sure.

I understand that it may be difficult to find resources to fix a version 
other than the latest one.  Another possible outcome is that this sort of 
thing will motivate TinyOS to switch to a new compiler version.  Of course 
there are issues with that too...

Compiler output follows.  It is not very informative since that function 
is nearly optimized away.

John



address@hidden:~$ avr-gcc -Os -fwrapv -S small.c -o -
        .file   "small.c"
        .arch avr2
__SREG__ = 0x3f
__SP_H__ = 0x3e
__SP_L__ = 0x3d
__tmp_reg__ = 0
__zero_reg__ = 1
        .global __do_copy_data
        .global __do_clear_bss
        .text
.global func_1
        .type   func_1, @function
func_1:
/* prologue: frame size=0 */
/* prologue end (size=0) */
        ldi r24,lo8(1)
        ldi r25,hi8(1)
/* epilogue: frame size=0 */
        ret
/* epilogue end (size=1) */
/* function func_1 size 3 (2) */
        .size   func_1, .-func_1
        .comm g_66,4,1
        .comm g_73,4,1
/* File "small.c": code    3 = 0x0003 (   2), prologues   0, epilogues   1 
*/




On Sun, 1 Jun 2008, Weddington, Eric wrote:

> Hi Dr. John,
>
> Are you using a particular WinAVR version? i.e. a patched avr-gcc 4.1.2?
> Or is this stock FSF 4.1.2?
>
> Can you post the compiler output?
>
> Sorry, but most of the developers are dealing with HEAD/4.4 or maybe
> 4.3.0. I understand that you're using 4.1.2 for TinyOS.
>
> Eric
>
> > -----Original Message-----
> > From:
> > address@hidden
> > [mailto:address@hidden
> > org] On Behalf Of John Regehr
> > Sent: Sunday, June 01, 2008 9:14 PM
> > To: address@hidden
> > Subject: [avr-gcc-list] wrong code from avr-gcc 4.1.2?
> >
> > In the code below, avr-gcc 4.1.2 wants to return 1 from func_1() when
> > compiling at -Os.  Specifically I'm compiling like this:
> >
> >    avr-gcc -fwrapv -Os -mmcu=atmega128 foo.c
> >
> > I believe the correct answer is 0 (this is what avr-gcc-4.2.2
> > returns at
> > all optimization levels).  I don't think the -fwrapv is relevant here
> > but include it to be on the safe side.
> >
> > John Regehr
> >
> >
> >
> > static inline unsigned long int
> > div_rhs(const long int rhs)
> > {
> >      if (rhs == 0) return 1;
> >      return rhs;
> > }
> >
> > unsigned long g_66;
> > long g_73;
> >
> > int func_1 (void)
> > {
> >    unsigned long l_86 = -1L;
> >    unsigned long l_93 = -9L;
> >    if ((l_86 >= g_73) < (1 / div_rhs (l_93)))
> >      return 1;
> >    else
> >      return 0;
> > }
> >
> >
> >
> >
> > _______________________________________________
> > AVR-GCC-list mailing list
> > address@hidden
> > http://lists.nongnu.org/mailman/listinfo/avr-gcc-list