[llvm] Mark permlane instructions as convergent (PR #142962)

[Jay Foad via llvm-commits]

jayfoad wrote:

This seems reasonable, given that all the permlane _intrinsics_ are marked as convergent. (Maybe TableGen should check that instruction selection patterns preserve the "convergent" property, like it does for some other properties.)


https://github.com/llvm/llvm-project/pull/142962