PING^3 for PR target/17836, PR c/10735, PR c++/16882, PR rtl-optimization/17860[3.4]

[Paolo Bonzini]

> Paolo> This one at least seems wrong to me.  Once more: unless Altivec is
> on, Altivec vector types *won't have vector modes, but BLKmode*.  The
> "else if (ALTIVEC_VECTOR_MODE (mode))" won't trigger!  That's why I did 
>  
> 	Why should parameters have stricter alignment if there is no SIMD
> unit?

Because otherwise the non-Altivec ABI breaks depending on whether there 
is a SIMD unit or not.

> 	Also, while V2DI can be packed into an Altivec register and one
> can apply a logical op, Altivec operations are not defined for those
> types -- it is not part of the ABI.  There is no defined way to load and
> store V2DI.  If you pun the type to load and store, you equally can pun
> the type to perform logical ops.

The idea is that the middle-end can pun the types automatically, and use 
v4si insns to perform v2di ops.  See tree-complex.c.

Paolo