8383832: AOTMode=required fails with "incompatible CompressedOops::base()"

[iklam]

Problem

In an AOT production run with -XX:AOTMode=required (or with the alias -XX:AOTMode=on), the JVM sometimes fail to start with the message:

[0.022s][error][aot,codecache,init] AOT Code Cache disabled: incompatible CompressedOops::base(): 0x0 vs current 0xa5a800000

This means that the AOT cache was created when the heap range is below 32GB, but in the production run, the heap is allocated above 32GB.

Solution:

Add a diagnostic option -XX:+AOTCompatibleOopCompression. This will force the HeapBasedNarrowOop to be used in both AOT assembly and production, so the AOT code cache is always compatible with the production run.

If you are planning to use -XX:AOTMode=required as a "fail-fast debugging aid" (see this note in the man page), your AOT cache should be created with -XX:+AOTCompatibleOopCompression

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Progress

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Issue

• JDK-8383832: AOTMode=required fails with "incompatible CompressedOops::base()" (Bug - P4)

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[mlbridge]

Webrevs

• 00: Full (6dea4f9f)

[dholmes-ora]

Just a drive-by comment.

[dholmes-ora]

Suggested change

	"Always use HeapBasedNarrowOop mode, so that AOT code can be " \
	"always work regardless of runtime heap range") \
	"Always use HeapBasedNarrowOop mode, so that AOT code will " \
	"always work regardless of runtime heap range") \

[dholmes-ora]

From the description and usage of this it does not seem to be a diagnostic flag at all.