RFR: 8322996: BoxLockNode creation fails with assert(reg < CHUNK_SIZE) failed: sanity [v3]

[Daniel Lundén]

On Wed, 17 Jan 2024 00:10:10 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

>> Yes, that is my intuition as well. Therefore, I'm left wondering if the [construction of `_inmask`](https://github.com/dlunde/jdk/blob/9ab6e561780aee0f2cc2f06cd40ec487d60fe39c/src/hotspot/share/opto/locknode.cpp#L51) in the `BoxLockNode` constructor is incorrect, as it always just sets a single bit in the mask (no matter the value of `sync_stack_slots()`). Should we perhaps change it to instead set the range [ reg, reg + sync_stack_slots() ) in `_inmask`?
>
> It is fine. Monitors use fixed stack slots which are not available to Register allocator: [compile.hpp#L315](https://github.com/openjdk/jdk/blob/master/src/hotspot/share/opto/compile.hpp#L315). Fixed stack slots reserved based on number monitors and etc. We don't do regmask operations on them.
> 
> `BoxLockNode::reg(box)` is only accessed in format output in `JVMState::format()` and when we generate debug info in `PhaseOutput::Process_OopMap_Node()`.
> 
> In general, in 64-bit VM long, double, oop/pointers values take 2 slots but their value is stored only in first slot (since slot's size is 64 bit). Don't ask why. It is convention in VM.

Thanks for the clarification. I'll go ahead with the proposed solution with `can_represent_sync` then (but I'll move it to `regmask.hpp`).

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PR Review Comment: https://git.openjdk.org/jdk/pull/17370#discussion_r1454948748