[foreign-preview] Integrated: 8282070: Drop workaround from memory segment implementation

[Maurizio Cimadamore]

On Thu, 17 Feb 2022 19:07:12 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

> Following some preliminary experiments (see [1]) it is now finally time to drop the various workarounds we have in the memory segment implementation. This patch removes two workarounds:
> 
> * special treatment for "small" segments (e.g. segments whose size fits in an int) - see `MemorySegment::isSmall`; these segments were special cased so that bound checks would only involve `int` comparisons. This has now been fixed in JDK-8276116, and special treatment is no longer required.
> 
> * special shortcuts to avoid extra alignment checks. Since when generating var handles from a layout we check most of the alignment constraints (except those involving the base address), in the past we have added a fastpath for these var handles, as C2 had trouble hoisting alignment checks outside of the loops. This has now been fixed in JDK-8277850 and is no longer required.
> 
> I have run benchmarks before and after and got identical results. Some benchmarkks in `ParallelSum` got a boost, but those always have noise, due to multi-threading.

This pull request has now been integrated.

Changeset: 78f02203
Author:    Maurizio Cimadamore <mcimadamore at openjdk.org>
URL:       https://git.openjdk.java.net/panama-foreign/commit/78f02203767cf4bac49eeea44be2844680dc728b
Stats:     252 lines in 14 files changed: 26 ins; 114 del; 112 mod

8282070: Drop workaround from memory segment implementation

Reviewed-by: jvernee, psandoz

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PR: https://git.openjdk.java.net/panama-foreign/pull/644