[llvm] [SimplifyCFG] When only one case value is missing, replace default with that case (PR #76669)

[Yingwei Zheng via llvm-commits]

dtcxzyw wrote:

Emm, this patch seems to increase the inline cost estimation of switch insts. Not sure it is a regression.
Please have a look at `bench/hermes/optimized/SourceMgr.cpp.ll`.
https://github.com/dtcxzyw/llvm-opt-benchmark/pull/80/files


https://github.com/llvm/llvm-project/pull/76669