[llvm] [DAGCombiner][VP] Add DAGCombine for VP_MUL (PR #80105)

[Min-Yih Hsu via llvm-commits]

mshockwave wrote:

> CC @mshockwave who might be able to advise on how we can add VP_* support

@jacquesguan you can try to use `SDPatternMatch::sd_context_match` along with VPMatchContext object to replace explicit calls to `VPMatchContext::match` in your code. I believe it will be pretty straightforward.

https://github.com/llvm/llvm-project/pull/80105