8354899: Reduce overhead associated with type switches

[liach]

The downcallHandle method in Linker has a complex implementation, and type switches is triggered in multiple places in that handle.

After bytestacks analysis of a simple program that links the native implementation of Class::forName0, it turns out that:

1. there are a few missed usages of type switch in ClassFile API
2. type switch can speed up generation by using explicit stack maps, as stack map gen is over 50% of the generation instructions because the switch is branch-heavy, but the frames are actually simple.

These two combined are not that significant in the overall overhead of downcallHandle, but would be helpful for other workloads.

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Issue

• JDK-8354899: Reduce overhead associated with type switches (Sub-task - P4)

Reviewers

• Adam Sotona (@asotona - Reviewer)

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[openjdk]

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

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

8354899: Reduce overhead associated with type switches

Reviewed-by: asotona

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At the time when this comment was updated there had been 25 new commits pushed to the master branch:

• c2e90bc: 8355363: [BACKOUT] 8354668: Missing REX2 prefix accounting in ZGC barriers leads to incorrect encoding
• 263983d: 8298733: Reconsider monitors_on_stack assert
• 27faf45: 8354826: Make ResolverConfigurationImpl.lock field final
• ... and 22 more: https://git.openjdk.org/jdk/compare/5264d80bea25a1ef98dae4633b04b16e8de6120f...master

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[liach]

This advanced switch prevents CodeBuilder::ifThen or ifThenElse from being used in early bootstrap.

[mlbridge]

Webrevs

• 01: Full - Incremental (2c17dd1c)
• 00: Full (cbc3fd34)

[liach]

Testing: tier 1-3

[asotona]

Both parts of this PR look good to me, however they seem to be unrelated.
I would suggest to create another PR for #1, as the Class-File API JDK boot safety is not related to the SUBJ.

[liach]

Done, reran jdk/jdk/classfile langtools/tools/javac/patterns jdk/java/lang/runtime tests.

[liach]

Split the ClassFile API boot safety into #24807.

[asotona]

I like that the performance of the Class-File API can be improved in critical use cases like this, even though we don't 100% eat our own dog food.

[liach]

Thanks for the reviews!

/integrate

[openjdk]

Going to push as commit bd1c53e.
Since your change was applied there have been 47 commits pushed to the master branch:

• ffe6a4f: 8355335: Avoid pattern matching switches in core ClassFile API
• 88e0b00: 8353298: AOT cache creation asserts with _array_klasses in an unregistered InstanceKlass
• adcaf01: 8355237: Upstream AOT test cases from Leyden repo to mainline
• ... and 44 more: https://git.openjdk.org/jdk/compare/5264d80bea25a1ef98dae4633b04b16e8de6120f...master

Your commit was automatically rebased without conflicts.

[openjdk]

@liach Pushed as commit bd1c53e.

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