Summary
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Deprecate the option -XX:CompactFields.  By default it is true, and setting to false will not lead to better performance or any observable benefits.

Problem
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Flags allowing users to affect the layout of fields in Java classes give users unwelcome control over internal implementation details.  This option causes fields smaller than long/double to be packed in the gap before the first long/double field in an object.  There are no reasonable use cases to not do this.  With @contended, padding can be added to prevent false sharing, if needed.

Deprecating and removing this option will allow for efficient implementation of inline types for valhalla.

Solution
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Deprecate the option and continue affect layout with the option.

Users will now get the following message when running: 'java -XX:+CompactFields ...'

Java HotSpot(TM) 64-Bit Server VM warning: Option CompactFields was deprecated in version 14.0 and will likely be removed in a future release.

Specification
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Deprecate the -XX:CompactFields option in JDK-14 and issue the above warning message when the option is used.