[llvm] [DAG] Add legalization handling for ABDS/ABDU (PR #92576)

[Björn Pettersson via llvm-commits]

bjope wrote:

> > @bjope If you can confirm these go away if we pull out the inner getNode() calls then we can make the change - but given how prevalent this is in the codebase, I don't know what we'd do to address it completely.
> 
> I'm analysing it further, and will prepare something for this specific case (if my current suspicion ends up being correct).
> 
> Had been nice with some kind of checked (clang-tidy) that would detect the "bad" coding pattern. But I don't know really if that is easy/feasible to implement. I often end up comparing debug outputs from different builds (we sometimes use gcc when building opt/llc in various automatic builds, and then I use clang myself and end up looking at diffs, and get lots of irrelevant diffs due to argument evaluation order. This time I think it actually impacted the backend optimizations as well and not only the order of debug printouts etc.

Turns out those diffs related to argument evaluation order was irrelevant for the failed test.
This pull request show what really caused the problem downstream: https://github.com/llvm/llvm-project/pull/102915
We've had some fixes in ScheduleDAG for many years, that impacted the abds.ll test case.

https://github.com/llvm/llvm-project/pull/92576