[llvm] [X86] Correct the cdisp8 encoding for VSCATTER/VGATHER prefetch (PR #122051)

[Craig Topper via llvm-commits]

topperc wrote:

> LGTM, thanks for the fix!

@phoebewang can you commit this? @michaeljclark probably doesn't have permission if this is their first PR.

https://github.com/llvm/llvm-project/pull/122051