8329998: Remove double initialization for parts of small TypeArrays in ZObjArrayAllocator

[xmas92]

JDK-8139457 introduced non-word aligned payloads for TypeArrays. This required adaptation in ZObjArrayAllocator segmented array allocator. But the implementation does this adaptation even when the size is small enough and dispatches the allocation to ObjArrayAllocator, which already handles clearing this memory.

Instead move the initialization of any unaligned payload start to after the segmented allocation decision.

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Issue

• JDK-8329998: Remove double initialization for parts of small TypeArrays in ZObjArrayAllocator (Enhancement - P4)

Reviewers

• Stefan Karlsson (@stefank - Reviewer)
• Guoxiong Li (@lgxbslgx - Reviewer)

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8329998: Remove double initialization for parts of small TypeArrays in ZObjArrayAllocator

Reviewed-by: stefank, gli

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[lgxbslgx]

Looks good. One suggestion.

[lgxbslgx]

Actually, only the type arrays whose element type is not double word can be 4-byte aligned. So this assertion could be !is_reference_type(element_type) && !is_double_word_type(element_type).

[stefank]

I think the point is that when it is not a reference type, it is OK to initialize with a plain 0.

[lgxbslgx]

May be better to treat the assertion as a more detailed guard or check. But I'm also OK with the current code.

[xmas92]

Thanks for the reviews. Reran testing after merge.
/integrate

[openjdk]

Going to push as commit 96c5c3f.
Since your change was applied there have been 21 commits pushed to the master branch:

• ee4a9d3: 8321622: ClassFile.verify(byte[] bytes) throws unexpected ConstantPoolException, IAE
• ab8d7b0: 8324517: C2: crash in compiled code because of dependency on removed range check CastIIs
• fe8a2af: 8307778: com/sun/jdi/cds tests fail with jtreg's Virtual test thread factory
• 95f79c6: 8332253: Linux arm32 build fails after 8292591
• b687aa5: 8332176: Refactor ClassListParser::parse()
• 4083255: 8316138: Add GlobalSign 2 TLS root certificates
• 43b109b: 8330066: HeapDumpPath and HeapDumpGzipLevel VM options do not mention HeapDumpBeforeFullGC and HeapDumpAfterFullGC
• 7cff04f: 8330276: Console methods with explicit Locale
• 8a4315f: 8331987: Enhance stacktrace clarity for CompletableFuture CancellationException
• 491b3b4: 8332256: Shenandoah: Do not visit heap threads during shutdown
• ... and 11 more: https://git.openjdk.org/jdk/compare/c642f44bbe1e4cdbc23496a34ddaae30990ce7c0...master

Your commit was automatically rebased without conflicts.

[openjdk]

@xmas92 Pushed as commit 96c5c3f.

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