RFR: 8324890: C2 SuperWord: refactor out VLoop, make unrolling_analysis static, remove init/reset mechanism [v4]

[Vladimir Kozlov]

On Sat, 3 Feb 2024 07:48:50 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

> And I see that the first (init_size) chunk is allocated from a pool. But subsequent chunks (grow) have "non-standard" length, and are malloc/free'd.

Yes, that was my concern.

There are chunks with different sizes: [arena.hpp#L66](https://github.com/openjdk/jdk/blob/master/src/hotspot/share/memory/arena.hpp#L66). Is your allocation sizes > 32*K `Chunk::size` "Default size of an Arena chunk"? `Arena::grow()` uses `MAX2(ARENA_ALIGN(x), (size_t) Chunk::size);`.
Which of SuperWord allocations are big? Can we split them to fit into 32K?

I think, this should not stop you from doing this refactoring. Yes, it will allow return memory back sooner and it is up to OS how it optimize it. I read your offline discussion with Johan. He has interesting suggestion fro growable arrays (use C heap).

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PR Comment: https://git.openjdk.org/jdk/pull/17624#issuecomment-1925448873