[PowerPC] use lvx + splat directly for aligned splat load

[shchenz]

Summary

This is to address review comments for https://reviews.llvm.org/D106555#inline-1079417

We can use lvx + splat 0(or biggest index on LE) directly for some aligned splat load instead of lvx + splat with a constructed mask.

[shchenz]

for power 9, use lxsibzx as it has the same latency with lvx but has more useable registers.

[shchenz]

gentle ping

[shchenz]

gentle ping

[nemanjai]

LGTM.

llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp

4473

Nit: can probably be added to line 4471 (except of course change the body to
AddrOp = N->getOperand(1)

[shchenz]

Thanks for your review @nemanjai

llvm/lib/Target/PowerPC/PPCISelDAGToDAG.cpp

4473

Will fix this in the commit.