Unnesting of nested subreg expressions

[James E Wilson]

Björn Haase wrote:
> So far, I now think that the solution of the issue would be to extend 
> gen_lowpart and gen_highpart so that they are able to handle also subreg 
> inputs and use them at all places that emmit RTL (i.e. expand and split).
> Question is whether I should try to simultaneously implement support for the 
> case of paradoxial subregs as input operand, once I am working on the code?

You were never very clear about what was wrong with gen_highpart and 
gen_lowpart with respect to subregs.  rtl examples are always helpful, 
e.g. showing RTL input and RTL output and pointing out what is wrong. 
gen_lowpart already has support for subreg input and presumably should work.

gen_lowpart is already pretty involved.  If you need something other 
than a trivial fix, it might be better to try to solve the problem in 
your md file.

I would suggest only trying to fix things that you have testcases for. 
So if you don't have a paradoxical subreg testcase, then don't try to 
fix it.  You might accidentally make things worse than they already are.
-- 
Jim Wilson, GNU Tools Support, http://www.SpecifixInc.com