[llvm] [X86] Drop instruction prefetch with unsupported operands in LowerPREFETCH (PR #225826)

[Demetrios Chiuratto Agourakis via llvm-commits]

agourakis82 wrote:

Note: I just noticed #219031 by @AZero13 targets the same issue (#218236) and was opened earlier; sorry I missed it. The approaches differ: #219031 maps the unsupported hints to PREFETCHIT0/PREFETCHIT1, while this PR drops them (same as when PREFETCHI is unavailable) and also covers the 32-bit case. Happy to defer to whichever approach reviewers prefer.

https://github.com/llvm/llvm-project/pull/225826