[llvm] [SimplifyCFG] Simplify switch instruction that has duplicate arms (PR #114262)

[Yingwei Zheng via llvm-commits]

dtcxzyw wrote:

> I think this PR is ready for another review. I got the regressions down to what I think is a manageable number, and I'm just about out of ideas for improvements.
> 
> ```
>   ruby/gb18030.ll 109396527 -> 116902986 +6.86%
>   oniguruma/gb18030.ll 113977357 -> 121380998 +6.50%
>   jq/gb18030.ll 113973358 -> 121299720 +6.43%
>   coreutils-rs/3fao74xaflt9jiyw.ll 190436589 -> 197202895 +3.55%
>   actix-rs/5g1vgjexs3y2qadw.ll 234899361 -> 241896579 +2.98%
> ```

Your last version of the patch crashed on many test cases:
```
2024-11-05T06:18:50.9026927Z qemu/disas_riscv.c.ll crash
2024-11-05T06:18:50.9027265Z qemu/linux-user_syscall.c.ll crash
2024-11-05T06:18:50.9027583Z duckdb/ub_duckdb_common.cpp.ll crash
2024-11-05T06:18:50.9027932Z duckdb/ub_duckdb_execution.cpp.ll crash
2024-11-05T06:18:50.9030885Z linux/filter.ll crash
2024-11-05T06:18:50.9031252Z linux/intel_display_power.ll crash
2024-11-05T06:18:50.9031564Z linux/hooks.ll crash
2024-11-05T06:18:50.9031946Z node/uv-common.ll crash
2024-11-05T06:18:50.9032237Z node/libnode.node_errors.ll crash
2024-11-05T06:18:50.9032557Z postgres/gram.ll crash
2024-11-05T06:18:50.9032887Z postgres/parse_agg.ll crash
2024-11-05T06:18:50.9033186Z postgres/tablecmds.ll crash
2024-11-05T06:18:50.9033509Z postgres/explain.ll crash
2024-11-05T06:18:50.9033857Z postgres/utility.ll crash
2024-11-05T06:18:50.9034163Z postgres/wait_event.ll crash
```



https://github.com/llvm/llvm-project/pull/114262