[RISCV] Add Commutable flag to XNOR. (#147654)

Author: topperc

llvm/lib/Target/RISCV/RISCVInstrInfoZb.td

@@ -272,7 +272,7 @@ def ANDN  : ALU_rr<0b0100000, 0b111, "andn">,
             Sched<[WriteIALU, ReadIALU, ReadIALU]>;
 def ORN   : ALU_rr<0b0100000, 0b110, "orn">,
             Sched<[WriteIALU, ReadIALU, ReadIALU]>;
-def XNOR  : ALU_rr<0b0100000, 0b100, "xnor">,
+def XNOR  : ALU_rr<0b0100000, 0b100, "xnor", Commutable=1>,
             Sched<[WriteIALU, ReadIALU, ReadIALU]>;
 } // Predicates = [HasStdExtZbbOrZbkb]