[InstCombine] Add more tests. NFC.

Author: dtcxzyw

llvm/test/Transforms/InstCombine/icmp-select.ll

@@ -726,6 +726,23 @@ entry:
   ret i1 %res
 }
 
+define i1 @discr_eq_add_commuted_implies_poison(i8 %a, i8 %b, i8 %c, i1 %cond1, i1 %cond2) {
+; CHECK-LABEL: @discr_eq_add_commuted_implies_poison(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TMP0:%.*]] = select i1 [[COND1:%.*]], i8 [[B:%.*]], i8 0
+; CHECK-NEXT:    [[TMP1:%.*]] = select i1 [[COND2:%.*]], i8 [[C:%.*]], i8 [[B]]
+; CHECK-NEXT:    [[RES:%.*]] = icmp eq i8 [[TMP0]], [[TMP1]]
+; CHECK-NEXT:    ret i1 [[RES]]
+;
+entry:
+  %add1 = add i8 %a, %b
+  %sel1 = select i1 %cond1, i8 %add1, i8 %a
+  %add2 = add i8 %c, %a
+  %sel2 = select i1 %cond2, i8 %add2, i8 %add1
+  %res = icmp eq i8 %sel1, %sel2
+  ret i1 %res
+}
+
 define i1 @discr_eq_sub(i8 noundef %a, i8 %b, i8 %c, i1 %cond1, i1 %cond2) {
 ; CHECK-LABEL: @discr_eq_sub(
 ; CHECK-NEXT:  entry: