RE: [avr-gcc-list] GCC does useless 16-bit operations

[Eric Weddington]

> -----Original Message-----
> From: 
> address@hidden 
> [mailto:address@hidden
> org] On Behalf Of address@hidden
> Sent: Thursday, May 10, 2007 9:28 PM
> To: address@hidden
> Subject: [avr-gcc-list] GCC does useless 16-bit operations
> 
> For the C code:
<snip bloated code> 
> The C code:
> 
>   uint8_t temp = (tx_producer_index + 1U) % 64;
> 
> is much much better with 3.4.4:
> 
>     16de:       e0 91 f7 00     lds     r30, 0x00F7
>     16e2:       ef 5f           subi    r30, 0xFF       ; 255
>     16e4:       9e 2f           mov     r25, r30
>     16e6:       9f 73           andi    r25, 0x3F       ; 63
> 
<snip> 
> Is there something I should do to figure out what GCC thinks 
> it's doing?

To keep this issue from being lost in the email archives, could you do
this?:
- Fill out a GCC bug report
- Set the target to "avr"
- Set the keywords list to "missed-optimization"
- Put my email address in the CC list so I can keep track of it.

I agree the code should not be so bloated and that AVR GCC should do better.
It is a "missed optimization" type of bug. I cannot guarantee when it will
get fixed as we could always use more volunteers.

Thanks,
Eric