[cft] subreg validation patch

[Eric Botcazou]

> Saw it myself... finally.  Got a fix for it too.  Nicely irritating
> in that we didn't actually *want* a subreg, we just created it so
> that we could pass it to some subroutine, when we should have been
> using subreg_regno_offset in the first place.

Thanks.  I spotted the problem with Jakub's struct-layout testsuite.  Jakub 
may have advertised it as a compatibility testsuite, but it is extremely 
useful in stressing the middle-end and the back-end (as of today, the only 
failures on the SPARC are due to the subreg representability problem).

-- 
Eric Botcazou