[SPARK-57202][SQL] Skip dead null checks in In expression codegen for non-null list elements

[gengliangwang]

What changes were proposed in this pull request?

In's whole-stage codegen emits, for each list element x:

if (x.isNull) {
  inTmpResult = -1; // HAS_NULL
} else if (value == x) {
  inTmpResult = 1;  // MATCHED
  continue;
}

IN lists are usually constant literals, so x.isNull is the literal false and the HAS_NULL branch is dead (if (false) { inTmpResult = -1; } else if ...). This PR emits only the equality check when x.isNull == FalseLiteral. Symmetrically, when an element is statically null (x.isNull == TrueLiteral, e.g. IN (NULL, ...)), only the HAS_NULL assignment is emitted and the dead equality check is dropped.

Why are the changes needed?

Sub-task of SPARK-56908 (reduce generated Java size in whole-stage codegen). Dumping the TPC-DS whole-stage codegen shows ~348 dead if (false) { inTmpResult = -1; } else if (...) blocks from In over literal lists. Emitting only the live branch removes the dead conditional from the generated code.

Does this PR introduce any user-facing change?

No. The generated code is smaller but evaluates IN with identical (including null) semantics: a statically non-null element can never set HAS_NULL, and a statically null element can never match, so dropping those dead branches is equivalent.

How was this patch tested?

Behavior-preserving change covered by PredicateSuite (70 tests, including In with null list elements and a null left-hand value), all pass. Additionally verified by re-dumping the TPC-DS whole-stage codegen: the ~348 dead if (false) blocks in In are gone and every generated subtree still compiles.

Was this patch authored or co-authored using generative AI tooling?

Generated-by: Claude Code (Opus 4.8)