[lilliput-jdk17u:lilliput] RFR: 8317957: [Lilliput/JDK17] Make C2 LoadNKlassCompactHeader more robust [v4]

[Aleksey Shipilev]

On Thu, 12 Oct 2023 09:24:36 GMT, Roman Kennke <rkennke at openjdk.org> wrote:

>> Backport of https://github.com/openjdk/lilliput/pull/111. I needed to extract the body into helper methods in order to match mainline version. Other than that, the changes are identical.
>> 
>> Lilliput's C2 code for generating LoadNKlass currently assumes that the disp of the incoming address is klass_offset_in_bytes. It then extracts the base register and loads from the mark_offset_in_bytes instead.
>> Sometimes (apparently very rarely) it happens that C2 emits code that pre-adds obj+klass_offset into a register, and uses that as base, but with offset 0. In this case we would trip the assert or crash in release builds.
>> 
>> - [x] specjvm derby (which triggered the bug)
>> - [x] tier1 x86_64 +UCOH
>> - [x] tier1 aarch64 +UCOH
>
> Roman Kennke has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Accept indexed address

Marked as reviewed by shade (Reviewer).

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PR Review: https://git.openjdk.org/lilliput-jdk17u/pull/57#pullrequestreview-1674090350