[llvm] [RISCV] Disable generic DAG combines at -O0 to preserve debuggability (PR #219082)

[Jim Lin via llvm-commits]

tclin914 wrote:

> Does this mean better debug info or something else?
> 
> I don't have a problem with it per-se, it's just good to understand why for instance the generic version of the hook isn't implemented this way.
> 
> Are there target dag combines we should be examining and turning off?

This is just for better debug info.

The reason why the generic version of the hook isn't implemented this way was explained here https://github.com/llvm/llvm-project/pull/176304#discussion_r2907942165

I think there are still target dag combines we should turn it off with O0 optimization level.

https://github.com/llvm/llvm-project/pull/219082