8358104: Fix ZGC compilation error on GCC 10.2

[MaxXSoft]

JDK-8350441 introduced Mapped Cache for ZGC. However, the constructor of ZMappedCache uses brace-initialization for _size_class_lists, i.e. a ZList array. ZList is a class with a deleted copy constructor and an explicit destructor, and when its array is brace-initialized in the constructor, it triggers GCC bug 63707. A short example to reproduce this bug: https://godbolt.org/z/3397bxc73

The bug causes compilation error of ZGC on GCC versions 10.1 to 10.2. Considering OpenJDK compilation is still requires GCC 10 or higher, this should be recorded as a bug.

This patch uses value-initialization for _size_class_lists instead of brace-initialization, which should be semantically equivalent and work on all GCC versions.

---

Progress

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Issue

• JDK-8358104: Fix ZGC compilation error on GCC 10.2 (Bug - P4)

Reviewers

• Kim Barrett (@kimbarrett - Reviewer)
• Joel Sikström (@jsikstro - Committer)

Reviewing

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[openjdk]

@MaxXSoft This change now passes all automated pre-integration checks.

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After integration, the commit message for the final commit will be:

8358104: Fix ZGC compilation error on GCC 10.2

Reviewed-by: kbarrett, jsikstro

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At the time when this comment was updated there had been 6 new commits pushed to the master branch:

• 566e3b2: 8357253: Test test/jdk/sun/security/ssl/SSLSessionImpl/ResumeClientTLS12withSNI.java writes in src dir
• e33eeee: 8341311: [Accessibility,macOS,VoiceOver] VoiceOver announces incorrect number of items in submenu of JPopupMenu
• 6f9e117: 8356246: C2: Compilation fails with "assert(bol->is_Bool()) failed: unexpected if shape" in StringConcat::eliminate_unneeded_control
• ... and 3 more: https://git.openjdk.org/jdk/compare/a05f9dea18ec812abad1dbe0084c0c58384a9076...master

As there are no conflicts, your changes will automatically be rebased on top of these commits when integrating. If you prefer to avoid this automatic rebasing, please check the documentation for the /integrate command for further details.

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[openjdk]

@MaxXSoft The following label will be automatically applied to this pull request:

• hotspot-gc

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[mlbridge]

Webrevs

• 00: Full (1234f07a)

[kimbarrett]

The change seems okay, though a bit disappointing that it's needed.

The referenced gcc bug seems to have been fixed in gcc11, with backports to
gcc10.3 and gcc9.4. The minimum supported compiler version has always been
somewhat approximate, since there isn't regular testing reported for what are
often rather old versions. Sometimes we just decide to force an update to the
required minimum rather than working around an issue like this.

I wonder why that version is still in use?

[MaxXSoft]

@kimbarrett Thanks for your review!

I wonder why that version is still in use?

My development environment is an Alibaba Cloud ECS server, with Alibaba Cloud Linux 3.2104 LTS. The default C++ compiler in this OS happens to be GCC 10.2.1.

[MaxXSoft]

@jsikstro Thanks for your review!

/integrate

[openjdk]

@MaxXSoft
Your change (at version 1234f07) is now ready to be sponsored by a Committer.

[jsikstro]

/sponsor

[openjdk]

Going to push as commit a0eb190.
Since your change was applied there have been 6 commits pushed to the master branch:

• 566e3b2: 8357253: Test test/jdk/sun/security/ssl/SSLSessionImpl/ResumeClientTLS12withSNI.java writes in src dir
• e33eeee: 8341311: [Accessibility,macOS,VoiceOver] VoiceOver announces incorrect number of items in submenu of JPopupMenu
• 6f9e117: 8356246: C2: Compilation fails with "assert(bol->is_Bool()) failed: unexpected if shape" in StringConcat::eliminate_unneeded_control
• ... and 3 more: https://git.openjdk.org/jdk/compare/a05f9dea18ec812abad1dbe0084c0c58384a9076...master

Your commit was automatically rebased without conflicts.

[openjdk]

@jsikstro @MaxXSoft Pushed as commit a0eb190.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.

[jsikstro]

Thanks for the fix @MaxXSoft! Just FYI, we usually allow PRs to be open for at least 24 hours to make sure reviewers from different time zones have a chance to see a PR, but this is a very small change. I'm not sure it was my place (seeing I'm only a Commiter and not a Reviewer) to say this is trivial, but I'd strongly argue it is.

https://openjdk.org/guide/index.html#life-of-a-pr