[llvm] [DAGCombine] Add all users of the instruction recursively into worklist when an instruction is simplified (PR #91772)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

This is trying to achieve the same thing as the topological dag patches (https://github.com/RKSimon/llvm-project/tree/perf/topological-dag / https://github.com/llvm/llvm-project/pull/77475) 

Which results in a reduction in compile time: (https://llvm-compile-time-tracker.com/?config=Overview&stat=instructions%3Au&remote=RKSimon)

There is the same problem with those patches as this PR - massive test churn including a large number of DAG combines that need fixing as they haven't always had to take into account that their operands might have already been combined further.

I'm not sure how best to split this work tbh.

https://github.com/llvm/llvm-project/pull/91772