[llvm] [GVNSink] Fix non-determinisms by using Depth-First ordering (PR #90995)

[via llvm-commits]

hiraditya wrote:

> SplitBlockPredecessors invalidates the DFS numbering, I think.

Makes sense to just update DFSNumbes with each split block.

> Also, SplitBlockPredecessors changes the predecessor list of a basic block, which I think needs to invalidate any ModelledPHI referring to that block?

AFAICT all the ModelledPHI are created for a specific SinkBB (in SinkBB and analyzeInstructionForSinking functions) and then destroyed.

https://github.com/llvm/llvm-project/pull/90995