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

[Jianjian Guan via llvm-commits]

jacquesguan 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.

Thanks, I changed `Match` to `sd_context_match`.

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