[LLVMdev] Extending vector operations

[David Greene]

On Tuesday 22 July 2008 08:33, Stefanus Du Toit wrote:

> Right, the type that needs to be used at the birthpoint of the value
> will generally be determined by the operation being performed to
> define it. At uses, that representation will have to be converted.

Why would this ever happen?  If the mask doesn't match the vector
length of the operation, isn't the operation undefined?

I suppose a mask could be longer than the vector length and still
have defined behavior, but this kind of mismatch strikes me as odd.

> There are some operations which may not provide a unique
> representation at a definition. Phi statements are the most obvious
> ones - if a phi statement joins two boolean vectors of different
> representations, the optimal choice of the result may depend on where
> that result is used.

Again, why would this happen?  Does a phi today ever join two vectors
of different type/length?

                                                -Dave