rfc: auto-casted vector types

[Jim Wilson]

Aldy Hernandez <aldyh@redhat.com> writes:

> The PPC E500 API specifies that vector types of type __ev64_opaque__
> (V2SImode) can interconvert with other vector types without a cast.

Is there any publicly available documentation?  My copy of the draft docs
say they are Motorola confidential.  If there is documentation available,
it would be useful to point to it somewhere.

I tried searching the Motorola web site.  I found Altivec PIM documentation,
but no SPE PIM documentation.

> 	* doc/tm.texi: Document TARGET_VECTOR_TYPES_COMPATIBLE.
> 	* c-typeck.c (comptypes): Take into account
> 	TARGET_VECTOR_TYPES_COMPATIBLE.
> 	(convert_for_assignment): Same.
>       ...

The patch looks pretty reasonable to me also.  I agree with Zack's suggestions.

It might be useful to note in the comments in the rs6000 file that the
current implementation has a known flaw.  It pretends that V2SI is the opaque
vector type.  This means that it accidentally allows conversions to/from the
V2SI vector type without explicit casts.  In order to fix this, we need to
use a different otherwise unused vector type for the opaque vector type.
Nick started on a patch to do this, but didn't have enough time to finish it.

Jim