RFR: 8345647: Fix recent NULL usage backsliding in Shenandoah

[Kim Barrett]

On Mon, 9 Dec 2024 15:29:56 GMT, Sonia Zaldana Calles <szaldana at openjdk.org> wrote:

> Hi all, 
> 
> This PR addresses [8345647](https://bugs.openjdk.org/browse/JDK-8345647) addressing uses of `NULL` in Shenandoah. These should be replaced to `null`. 
> 
> I verified where those uses are with: 
> `git show <commit-id> --name-only | while read file; do echo "File: $file"; git diff <commit-id> -- "$file" | grep -n -F 'NULL'; done`
> 
> The relevant output: 
> 
> File: src/hotspot/cpu/ppc/gc/shenandoah/shenandoahBarrierSetAssembler_ppc.cpp
> 9:-  // No need for post barrier if storing NULL
> File: src/hotspot/share/gc/shenandoah/c2/shenandoahBarrierSetC2.cpp
> 9:-    // must be either an oop or NULL
> 12:     if (t == TypePtr::NULL_PTR || t == Type::TOP)
> 
> 
> Changes affect comments only. 
> 
> Thanks, 
> Sonia

Unfortunately, this change was incomplete.  It missed these:

./share/gc/shenandoah/shenandoahFreeSet.cpp:  // Overwrite with non-zero (non-NULL) values only if necessary for allocation bookkeeping.
./share/gc/shenandoah/shenandoahGenerationalEvacuationTask.cpp:      assert(obj->klass() != nullptr, "klass should not be NULL");

In both of those lines, s/NULL/null/

Sorry I didn't point this out before this PR was integrated.  I only noticed the PR this morning. Guess we'll need
another JBS issue and PR...

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PR Comment: https://git.openjdk.org/jdk/pull/22647#issuecomment-2536264494