[clang] [llvm] [AMDGPU] Change CF intrinsics lowering to reconverge on predecessors. (PR #92809)

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alex-t wrote:

> @alex-t Just curious about the status of this PR. Both this PR and the register-allocation PR by CD will have significant impact to the generated code. If we decide this is the right direction, then I feel it would be better to get it in earlier, so we can access its impact in our downstream work.

I am sorry but I haven't updated this PR for too long time. We recently decided that it worth trying to upstream.
I am going to close this one and create the new one. My apologies for the inconvenience. 

https://github.com/llvm/llvm-project/pull/92809