[SPARK-21351][SQL] Update nullability based on children's output
## What changes were proposed in this pull request?
This pr added a new optimizer rule `UpdateNullabilityInAttributeReferences ` to update the nullability that `Filter` changes when having `IsNotNull`. In the master, optimized plans do not respect the nullability when `Filter` has `IsNotNull`. This wrongly generates unnecessary code. For example:
```
scala> val df = Seq((Some(1), Some(2))).toDF("a", "b")
scala> val bIsNotNull = df.where($"b" =!= 2).select($"b")
scala> val targetQuery = bIsNotNull.distinct
scala> val targetQuery.queryExecution.optimizedPlan.output(0).nullable
res5: Boolean = true
scala> targetQuery.debugCodegen
Found 2 WholeStageCodegen subtrees.
== Subtree 1 / 2 ==
*HashAggregate(keys=[b#19], functions=[], output=[b#19])
+- Exchange hashpartitioning(b#19, 200)
+- *HashAggregate(keys=[b#19], functions=[], output=[b#19])
+- *Project [_2#16 AS b#19]
+- *Filter isnotnull(_2#16)
+- LocalTableScan [_1#15, _2#16]
Generated code:
...
/* 124 */ protected void processNext() throws java.io.IOException {
...
/* 132 */ // output the result
/* 133 */
/* 134 */ while (agg_mapIter.next()) {
/* 135 */ wholestagecodegen_numOutputRows.add(1);
/* 136 */ UnsafeRow agg_aggKey = (UnsafeRow) agg_mapIter.getKey();
/* 137 */ UnsafeRow agg_aggBuffer = (UnsafeRow) agg_mapIter.getValue();
/* 138 */
/* 139 */ boolean agg_isNull4 = agg_aggKey.isNullAt(0);
/* 140 */ int agg_value4 = agg_isNull4 ? -1 : (agg_aggKey.getInt(0));
/* 141 */ agg_rowWriter1.zeroOutNullBytes();
/* 142 */
// We don't need this NULL check because NULL is filtered out in `$"b" =!=2`
/* 143 */ if (agg_isNull4) {
/* 144 */ agg_rowWriter1.setNullAt(0);
/* 145 */ } else {
/* 146 */ agg_rowWriter1.write(0, agg_value4);
/* 147 */ }
/* 148 */ append(agg_result1);
/* 149 */
/* 150 */ if (shouldStop()) return;
/* 151 */ }
/* 152 */
/* 153 */ agg_mapIter.close();
/* 154 */ if (agg_sorter == null) {
/* 155 */ agg_hashMap.free();
/* 156 */ }
/* 157 */ }
/* 158 */
/* 159 */ }
```
In the line 143, we don't need this NULL check because NULL is filtered out in `$"b" =!=2`.
This pr could remove this NULL check;
```
scala> val targetQuery.queryExecution.optimizedPlan.output(0).nullable
res5: Boolean = false
scala> targetQuery.debugCodegen
...
Generated code:
...
/* 144 */ protected void processNext() throws java.io.IOException {
...
/* 152 */ // output the result
/* 153 */
/* 154 */ while (agg_mapIter.next()) {
/* 155 */ wholestagecodegen_numOutputRows.add(1);
/* 156 */ UnsafeRow agg_aggKey = (UnsafeRow) agg_mapIter.getKey();
/* 157 */ UnsafeRow agg_aggBuffer = (UnsafeRow) agg_mapIter.getValue();
/* 158 */
/* 159 */ int agg_value4 = agg_aggKey.getInt(0);
/* 160 */ agg_rowWriter1.write(0, agg_value4);
/* 161 */ append(agg_result1);
/* 162 */
/* 163 */ if (shouldStop()) return;
/* 164 */ }
/* 165 */
/* 166 */ agg_mapIter.close();
/* 167 */ if (agg_sorter == null) {
/* 168 */ agg_hashMap.free();
/* 169 */ }
/* 170 */ }
```
## How was this patch tested?
Added `UpdateNullabilityInAttributeReferencesSuite` for unit tests.
Author: Takeshi Yamamuro <yamamuro@apache.org>
Closes #18576 from maropu/SPARK-21351.
5197562afe