Avoid invalid RTL sharing

[Jan Hubicka]

Hi,
> 
> This is OK for mainline.  Thanks for taking the time to hunt down these
> internal invariant violations.  Presumably, there'll be negligible effects
> on memory usage with this change?  If your memory usage tester complains
> after you check this in, there are some places we can be clever to avoid
> calling copy_rtx, but I doubt this is worth the additional effort.

Just for a record, memory checker didn't complained about this patch at
all. The copying really happens in quite rare corner cases (this is also
why the bugs like this stays latent for years).
> 
> p.s. Period after "Copy stored_mode" in the i386.c ChangeLog entry above.

Oops, I forgot about that while comitting.  I will try to mind adding it
on my next commit.  I am sorry for that!

Thanks,
Honza
> 
> Roger
> --