[llvm] Riscv branch peephole opt (PR #90451)

[Zhijin Zeng via llvm-commits]

zengdage wrote:

> Is this a widespread problem? In my local testing I see 2 places in perlbench.
> 
> Do you expect a performance gain from fixing this on perlbench?
> 
> I'm hesitant to add a new pass for a problem that occurs twice if it doesn't improve performance.

Negligible  performance gain for perlbench, may be 0.1%. 


https://github.com/llvm/llvm-project/pull/90451