ARM/getting rid of superfluous zero extension

[Eric Botcazou]

> Any suggestion about how I could avoid generating this zero_extension?

Redundant extensions have been a hot topic for some time.  The combiner should 
catch the local easy cases, we have ree.c for the nonlocal easy cases and Tom 
recently posted:
  http://gcc.gnu.org/ml/gcc-patches/2012-07/msg00408.html
which should catch more complex cases.

I guess someone should gather the various missed optimization cases, draw a 
global picture of the situation and see how the various approaches could be 
fitted together.

-- 
Eric Botcazou