autoinc / postinc not used

[Oleg Endo]

Hi,


On Tue, 2024-01-16 at 21:02 +0100, stefan@franke.ms wrote:
> Hi all,
> 
>  
> 
> I work a lot with the good old m68k target where post-increment is supported, and I was surprised that there almost no post-increments are used in the generated code.
> 
> This simple code:
> 
>  
> 
> void memclr (int length, long * ptr) {
> 
>   for(;length--;){
> 
>     *ptr++= 0;
> 
>   }
> 
> } 
> 
>  
> 
> does not use post-increments on AVR or SH. See also https://godbolt.org/z/fTvdv65rr
> 
> 

This issue has been around for a very long time.  I guess auto-inc is not
important enough on modern architectures to be of a major concern.

On SH{1,2,3,4} post-inc is only available for mem stores, not for mem loads.
SH2A adds support for stores with post-inc.  You have to specify "-mb -m2a"
for that, as the default target of sh-elf is SH1 (-m1).  But yeah, it's also
not utilized in this case.

Cheers,
Oleg