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8283175: Add equals/hashcode to MemorySegment #671



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@mcimadamore mcimadamore commented Mar 15, 2022

When looking at the API, we realized that MemorySegment is the only class not to expose equals/hashcode (MemoryLayout, MemoryAddress and MemorySession do). This makes it difficult to e.g. use a MemorySegment as a map key.

This patch adds equals/hashcode; the behavior is that of a shallow comparison - e.g. equals makes sure that the two segments point to the same memory region and have same spatial and temporal bounds. Read-only status is ignored by the comparison (on the basis that the segment is still pointing to the same memory region). And, since comparing memory session uses MemorySession::equals, segments backed by different "views" of the same session will also turn out to be equal (which also makes sense).

To perform a deeper comparison, clients can go through the MemorySegment::mismatch path, but I don't think that's a useful implementation for equals/hashCode (even though that's how byte buffers behave - but then, byte buffers do not provide a mismatch method).

When fixing this I realized that the equals method for FunctionDescriptor did not take into account the variable arity index, so I've fixed that too (and also tweaked the toString method to take that into account as well). Doing this revealed an issue in some of the calling convention tests, where we passed a variable arity descriptor as the expected descriptor, where in reality the calling convention "flattens" the variable arity descriptor into a specialized, fixed-arity one.


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$ git fetch pull/671/head:pull/671
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Update a local copy of the PR:
$ git checkout pull/671
$ git pull pull/671/head

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Checkout this PR locally:
$ git pr checkout 671

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bridgekeeper bot commented Mar 15, 2022

👋 Welcome back mcimadamore! A progress list of the required criteria for merging this PR into foreign-preview will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

@openjdk openjdk bot added the rfr Ready for review label Mar 15, 2022
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openjdk bot commented Mar 15, 2022

@mcimadamore This change now passes all automated pre-integration checks.

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After integration, the commit message for the final commit will be:

8283175: Add equals/hashcode to MemorySegment

Reviewed-by: sundar

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@openjdk openjdk bot added the ready Ready to be integrated label Mar 15, 2022
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openjdk bot commented Mar 15, 2022

Going to push as commit 5b15ef7.

@openjdk openjdk bot added the integrated Pull request has been integrated label Mar 15, 2022
@openjdk openjdk bot closed this Mar 15, 2022
@openjdk openjdk bot removed ready Ready to be integrated rfr Ready for review labels Mar 15, 2022
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openjdk bot commented Mar 15, 2022

@mcimadamore Pushed as commit 5b15ef7.

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