[llvm] [RISC-V][ISel] Remove redundant czero.eqz like 'czero.eqz a0, a0, a0' (PR #90208)

[Yingwei Zheng via llvm-commits]

================
@@ -7503,6 +7503,17 @@ SDValue RISCVTargetLowering::lowerSELECT(SDValue Op, SelectionDAG &DAG) const {
       return DAG.getNode(ISD::ADD, DL, VT, CMOV, RHSVal);
     }
 
+    // c = setcc f, 0, seteq
+    // (select c, t, f) -> (or f, (czero_nez t, f))
----------------
dtcxzyw wrote:

> Emm, it would be better to add the following folds in `RISCVInstrInfoZicond.td`:
> 
> ```
> def : Pat<(XLenVT (riscv_czero_eqz GPR:$rs1, (riscv_setne (XLenVT GPR:$rs1)))),
>           (COPY GPR:$rs1)>;
> def : Pat<(XLenVT (riscv_czero_nez GPR:$rs1, (riscv_seteq (XLenVT GPR:$rs1)))),
>           (COPY GPR:$rs1)>;
> ```

Sorry, it is incorrect.

https://github.com/llvm/llvm-project/pull/90208