[llvm] [PowerPC] custom constant scalar_to_vector on pwr7 (PR #109850)

[via llvm-commits]

RolandF77 wrote:

> Might be a dumb question, but is it accurate to specifically say P7 in the title, when it affects more than just P7 (at least that is what it looks like from the tests)?

The title mentions pwr7 because that is the interesting case. Currently this case is hit on pwr8+ in 32-bit mode as well, but that is a bug - scalar_to_vector should really be legal there. Processors older than pwr7 that have vectors will also be hit for some types but are not really interesting for performance. pwr7 is mostly interesting for ISVs building for it and running on something newer. I mean, I can change the title if you like, but that's why it says pwr7.

https://github.com/llvm/llvm-project/pull/109850