[llvm] [NVPTX] Reland `mad.wide` combine under (default off) CLI option (PR #160214)

[Artem Belevich via llvm-commits]

Artem-B wrote:

I've poked at the SASS a bit and indeed, ptxas does something rather strange: https://godbolt.org/z/bvb47sWYc

In both cases the base address addition appears to be "baked" into the load instruction itself.
I guess ptxas trips on attempting to extract the base address back from the `mad.wide`, while it can handle it in mul/add case.




https://github.com/llvm/llvm-project/pull/160214