[llvm] [RISCV] Use `experimental-p` extension for zero-extended narrow unsigned types (PR #213260)

[Craig Topper via llvm-commits]

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topperc wrote:

Is this worse for code size when Zca and Zcb are enabled? c.add+c.add+c.zext.b would be 6 bytes, padd.b+padd.b is 8 bytes.

https://github.com/llvm/llvm-project/pull/213260