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

[Phoebe Wang via llvm-commits]

phoebewang wrote:

> these vector scatter and gather prefetch instructions also have an unusual k mask operand position but I have not addressed this with this patch as I am unsure how to change the Intel format in the tablegen file.

You can change `"\t{$src {${mask}}|{${mask}}, $src}"` to `"\t$src $mask"`

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