[llvm] [DAG] Remove OneUse restriction on sext when folding (shl (sext (add_nsw x, c1)), c2) (PR #68972)

[via llvm-commits]

LiqinWeng wrote:

> regression

1. Test X86/pr65895.ll also regression（-mtriple=riscv64）
2. There is indeed no benefit in using x86 to test case riscv-shifted-extend.ll
So I don't know how to deal with it， should i remove the hasOneuse?


https://github.com/llvm/llvm-project/pull/68972