[LoongArch] Add a test for spurious mask removal. NFC

Link: #99272 (comment)

Author: heiher

llvm/test/CodeGen/LoongArch/andn-icmp.ll

@@ -601,3 +601,25 @@ define i1 @andn_icmp_ult_i8_nn(i8 %a, i8 %b) nounwind {
   %cmp = icmp ult i8 %and, %b
   ret i1 %cmp
 }
+
+define i1 @andn_icmp_eq_i8_i32(i8 signext %a, i8 signext %b) nounwind {
+; LA32-LABEL: andn_icmp_eq_i8_i32:
+; LA32:       # %bb.0:
+; LA32-NEXT:    andn $a0, $a1, $a0
+; LA32-NEXT:    andi $a0, $a0, 255
+; LA32-NEXT:    sltui $a0, $a0, 1
+; LA32-NEXT:    ret
+;
+; LA64-LABEL: andn_icmp_eq_i8_i32:
+; LA64:       # %bb.0:
+; LA64-NEXT:    andn $a0, $a1, $a0
+; LA64-NEXT:    andi $a0, $a0, 255
+; LA64-NEXT:    sltui $a0, $a0, 1
+; LA64-NEXT:    ret
+  %x = zext i8 %a to i32
+  %y = zext i8 %b to i32
+  %not = xor i32 %x, -1
+  %and = and i32 %not, %y
+  %cmp = icmp eq i32 %and, 0
+  ret i1 %cmp
+}