[PowerPC] Fix vperm codegen

[maryammo]

Summary

Commit rG934d5fa2b8672695c335deed0e19d0e777c98403 changed the vperm codegen
for cases that vperm is not replaced by xxperm, this patch is to revert that.

[stefanp]

Thank you for fixing this.
I do have a couple of comments related to the fix.

llvm/lib/Target/PowerPC/PPCISelLowering.cpp

10204

I don't think you need to bother with this extra ternary operator.
Everywhere you use V1HasXXSWAPD or V2HasXXSWAPD seems to already be guarded by Opcode == PPCISD::XXPERM so it doesn't matter what value those two bool values have in cases when you are not using the XXPERM oeprand.

10261

Is it possible to have a swap on both sides?

10271

For this section how about:

if (Opcode == PPCISD::XXPERM && (V1HasXXSWAPD || V2HasXXSWAPD)) {
  /// Same code as above but you don't need to check that (V1HasXXSWAPD || V2HasXXSWAPD)
}

You don't need to go into the if statement at all if there isn't at least one XXSWAPD.

[maryammo]

llvm/lib/Target/PowerPC/PPCISelLowering.cpp

10261

I have not see such a case.
btw, this patch is to address the vperm issue, so we can look at the swap on both sides for xxperm if needed separately. Thanks.

[maryammo]

Address the review comments

[stefanp]

Thank you for fixing this!
LGTM.

[maryammo]

Address the review comments

[RKSimon]

@maryammo Please can you take a look at https://github.com/llvm/llvm-project/issues/61315 - it looks related to this patch (and D133700)