[patch] for PRs 27639 and 26719

[Eric Botcazou]

> However, since calculations are always done in the base type,
> considerations on whether subtypes are wrapping or not should be
> irrelevant, which probably means we are each talking about completely
> different things...

This is internal stuff.  The point is precisely to prevent the loop optimizers 
from generating IVs in the subtypes.  Maybe we can refine that and accept 
"well-behaved" subtypes but I don't think it's worthwhile.  That's why we 
need to coax the loop optimizer into not assuming that subtypes wrap, because 
it draws problematic conclusions from that.

-- 
Eric Botcazou