[llvm] [X86] Support EGPR (R16-R31) for APX (PR #67702)

[Jay Foad via llvm-commits]

jayfoad wrote:

> @jayfoad How far are we from removing LiveVariables completely?

Hard to say until we get there. The last time I tried enabling -early-live-intervals by default there were still a couple (but only a couple) of crashes/assertions caused by TwoAddressInstruction not updating LiveIntervals correctly.

After that, there is a huge amount of churn in the lit tests which makes it hard to spot potential problems. I pushed #67038 to mitigate that but reverted due to problems with LiveDebugVariables which I am still looking at.

After that, who knows? There could be more problems lurking.

https://github.com/llvm/llvm-project/pull/67702