[PATCH] D113178: [PowerPC] use right register class for input operand of XXPERMDIs

[Nemanja Ivanovic via Phabricator via llvm-commits]

nemanjai added a comment.

In D113178#3111575 <https://reviews.llvm.org/D113178#3111575>, @jsji wrote:

> ...
> But this does introduce confusion about register classes -- it is suspicious that `xxspltd` operate on `f0` instead of `vs0`.

Ha ha, yup! Confusion about register classes is kind of a fact of life with PPC's complex overlaying of registers in a single register file. It certainly takes some time to get your mind around FP/VR/VSR/ACC registers.

But in any case, the neat feature of something like `xxspltd vs34, f0, 0` is that you know that `vs0` is only expected to be partially defined. So seeing something like `xxspltd vs34, f0, 1` should set off some alarm bells because we are splatting what is expected to be undefined. No such determination can be made for `xxspltd vs34, vs0, 1` (without tracking down how `vs0` was defined).


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