Re: [avr-gcc-list] Mega 128 not optimising correctly ...

[E. Weddington]

On 11 Nov 2002 at 10:14, Rob Ward wrote:

> Hi Eric and others. I have used your suggestion below, but in some
> cases it does not compile as you have suggested. For example...
> 
> #define SetClockHigh() (PORTD |= 0x80) // set clock line high
> #define SetClockLow() (PORTD &= ~0x80) // set clock line low
> 
>  SetClockHigh(); // set clock line hi
>  5e: 97 9a  sbi 0x12, 7 ; 18
>  SetClockLow(); // set clock line low
>  60: 82 b3  in r24, 0x12 ; 18
>  62: 83 23  and r24, r19
>  64: 82 bb  out 0x12, r24 ; 18
> 
> This is using -O2 or -O3 optimisation. However if I change to -Os I
> get a mixture in various places...
> 
>  SetClockHigh(); // set clock line hi
>  b0: 97 9a  sbi 0x12, 7 ; 18
>  SetClockLow(); // set clock line low
>  b2: 3f e7  ldi r19, 0x7F ; 127
>  b4: 82 b3  in r24, 0x12 ; 18
>  b6: 83 23  and r24, r19
>  b8: 82 bb  out 0x12, r24 ; 18
> 
> and also...
> 
>  SetClockHigh(); // set clock line hi
>  84: 97 9a  sbi 0x12, 7 ; 18
>  SetClockLow(); // set clock line low
>  86: 97 98  cbi 0x12, 7 ; 18
> 
> Is this something that could be improved or am I missing something?
> 
> TIA.
> 
> Rob

The version of GCC that I use is 3.2 experimental, from the latest 
AVRFreaks distribution. For compiler flags I use -Os as well as
-std=gnu99. Does yours match, what do you use?

Let me know,

Thanks.
Eric
avr-gcc-list at http://avr1.org