Re: [avr-gcc-list] miscompilation: save/restore of clobbered registers

[Mudiaga Obada]

If r18 and r19 get clobbered, it's a avr-gcc feature. r16 - r17 is
preserved. See the avr-libc FAQ about register usage for more Info.

Jeyasankar Kottalam wrote:
> Hello,
> 
> With GCC 3.4.4 and 4.0.0 the following code is miscompiled; registers that the
> function modifies are not saved and restored when entering/leaving the
> function. We worked around the issue by adding explicit pushes and pops of
> registers r16 through r19 in our code.
> 
> typedef unsigned char u1;
> typedef unsigned long u4;
> 
> u4 sram_read_u4( u1 *ptr )
> {
>     return (((u4) *ptr) << 24)
>          | (((u4) *(ptr + 1)) << 16)
>          | (((u4) *(ptr + 2)) << 8)
>          | (((u4) *(ptr + 3)));
> }
>