Hi Rod,
Rod Boyce schrieb:
> I am witting some code for an 8051 and seeing that is looks to be
> missing an optimisation anyway I have distilled th ecode to this fragment:
>
> void display_update( unsigned char tens, unsigned char ones );
>
>
> void my_func( unsigned char my_value )
> {
> unsigned char d1;
> unsigned char d2;
>
>
> d1 = my_value % 10;
> d2 = my_value / 10;
>
> /* Do stuff with d1 & d1 */
> display_update( d2, d1 );
> }
>
> The list file shows me this:
> 110 ; test51.c:10: d1 = my_value % 10;
> 0002 75 F0 0A 111 mov b,#0x0A
> 0005 EA 112 mov a,r2
> 0006 84 113 div ab
> 0007 85 F0*00 114 mov _display_update_PARM_2,b
> 115 ; test51.c:11: d2 = my_value / 10;
> 000A 75 F0 0A 116 mov b,#0x0A
> 000D EA 117 mov a,r2
> 000E 84 118 div ab
> 000F F5 82 119 mov dpl,a
> 120 ; test51.c:14: display_update( d2, d1
> );
>
> I have tried swapping the modulo and div operation around but it doe snot
> seem to have any effect.
> So my question is am I missing a command line switch when I compile the file?
>
No the optimization you are requesting is not yet implemented.
You can help yourself by using an extra peephole file though.
(I'm appending the file)
replace {
mov b,%1
mov a,%2
div ab
mov %3,b
mov b,%1
mov a,%2
div ab
mov %4,a
} by {
mov b,%1
mov a,%2
div ab
mov %3,b
; peephole xxx.a optimized modulo and division
mov %4,a
} if notVolatile(%1 %2), operandsNotRelated(%1 %2 %3)
which you can use with the following command line:
sdcc -c --peep-file my_peeph.def --fverbose-asm divmod.c
and arrive at:
0002 75 F0 0A 117 mov b,#0x0A
0005 EA 118 mov a,r2
0006 84 119 div ab
0007 85 F0*00 120 mov _display_update_PARM_2,b
121 ; peephole xxx.a optimized modulo and
division
000A F5 82 122 mov dpl,a
123 ; divmod.c:15: display_update (d2, d1);
which is probably what you want:)
This optimization (unless others approve) will probably not make it into SDCC
2.9.0.
Greetings,
Frieder
// see mail on sdcc-user 2009-02-22
replace {
mov b,%1
mov a,%2
div ab
mov %3,b
mov b,%1
mov a,%2
div ab
mov %4,a
} by {
mov b,%1
mov a,%2
div ab
mov %3,b
; peephole xxx.a optimized modulo and division
mov %4,a
} if notVolatile(%1 %2), operandsNotRelated(%1 %2 %3)
replace {
mov b,%1
mov a,%2
div ab
mov %3,a
mov b,%1
mov a,%2
div ab
mov %4,b
} by {
mov b,%1
mov a,%2
div ab
mov %3,a
; peephole xxx.b optimized modulo and division
mov %4,b
} if notVolatile(%1 %2), operandsNotRelated(%1 %2 %3)
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