[patch, libfortran, RFC] Speed up cshift with array shift

[Dominique d'Humières]

Hi Thomas,

On my machine I get the following timings without the patch

 cpu time cshift dim=1   0.490763009    
 cpu time do loop dim=1    5.57969809E-02
 cpu time cshift dim=2   0.416319966    
 cpu time do loop dim=2   0.187106013    
 cpu time cshift dim=3    1.37362707    
 cpu time do loop dim=3    1.39690399    

and

 cpu time cshift dim=1   0.166012987    
 cpu time do loop dim=1    5.48990071E-02
 cpu time cshift dim=2   0.183587968    
 cpu time do loop dim=2   0.191835046    
 cpu time cshift dim=3    1.35024190    
 cpu time do loop dim=3    1.42215610    

with the patch. Do you understand why cshift is so slow for dim=3?

Thanks for working on this issue.

Dominique

PS See also pr45689.