gen_lowpart called where 'truncate' needed?

[Ian Lance Taylor]

Mat Hostetter <mhostetter@tilera.com> writes:

> Since the high bits are already zero, that would be less efficient on
> most platforms, so guarding it with something like this would probably
> be smarter:
>
>   if (targetm.mode_rep_extended (mode, GET_MODE(x)) == SIGN_EXTEND)
>     return simplify_gen_unary (TRUNCATE, mode, x, GET_MODE (x));
>
> I'm happy to believe I'm doing something wrong in my back end, but I'm
> not sure what that would be.  I could also believe these are obscure
> edge cases no one cared about before.  Any tips would be appreciated.

Interesting.  I think you are in obscure edge case territory.  Your
suggestion makes sense to me, and in fact it should probably be put
into gen_lowpart_common.

Ian