gengliangwang opened a new pull request, #56257:
URL: https://github.com/apache/spark/pull/56257
### What changes were proposed in this pull request?
`GenerateUnsafeProjection` writes each field as `if (${input.isNull}) {
setNull } else { write }` whenever the field's schema is nullable. When the
bound value is statically non-null its `isNull` is the literal `false`, so this
emits a dead `if (false) { setNullAt(i); } else { write(...); }`.
This PR skips the null check (and the dead `setNull` branch) when
`input.isNull == FalseLiteral`, emitting just the write -- the same code the
existing `!nullable` path already produces. Symmetrically, when `input.isNull
== TrueLiteral` (statically null), it emits only `setNull`. The `FalseLiteral`
comparison is the idiom already used in this file for the top-level
`zeroOutNullBytes` fast path.
Before (for a non-null value in a nullable-schema field):
```java
if (false) {
rowWriter.setNullAt(0);
} else {
rowWriter.write(0, value);
}
```
After:
```java
rowWriter.write(0, value);
```
### 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 ~358 such dead `if (false) {
setNullAt } else { write }` blocks; the schema marks the field nullable while
the bound value is statically non-null. Emitting only the write removes the
dead branch and the redundant conditional from the generated projection code.
### Does this PR introduce _any_ user-facing change?
No. The row writer's null bits are already cleared up front
(`resetRowWriter` / `zeroOutNullBytes`), so writing a non-null value without
`setNullAt` is exactly what the existing `!nullable` path does; results are
unchanged.
### How was this patch tested?
Behavior-preserving change covered by the existing projection suites:
`GeneratedProjectionSuite` and `UnsafeRowConverterSuite` (39 tests) pass.
Additionally verified by re-dumping the TPC-DS whole-stage codegen: the ~358
dead `if (false) { setNullAt }` blocks 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)
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