[llvm] [RISCV] Construct constants via instructions if materialization is costly (PR #86926)

[Wang Pengcheng via llvm-commits]

wangpc-pp wrote:

There is a problem that we will lowering `ISD::CTLZ/ISD::CTTZ` to `ISD::CTPOP` if `ISD::CTPOP` is `Legal` or `Custom`, which causes some regressions. I am still fixing it.

https://github.com/llvm/llvm-project/pull/86926