[External] : are CodeElements unique?

[Adam Sotona]

Hi Mark,
Code elements are generally not unique, so they cannot be used as keys in maps.

However, there are several approaches to work around it (based on the use case):

  *   If you need to iterate over a list of elements multiple times and then transform it – you can use the index of the element as a key.
  *   Or if you have a complex set of chained and nested transformations and need to mark a code element for later identification, you can bind a label (CodeBuilder::newBoundLabel) to a position before, after, or instead of the element. Labels are unique, and your subsequent transformations will receive a LabelTarget pseudo-instruction at the marked point, and LabelTarget::label will match the label you bound earlier.

Adam

From: classfile-api-dev <classfile-api-dev-retn at openjdk.org> on behalf of Mark Roberts <markro at cs.washington.edu>
Date: Wednesday, 7 May 2025 at 21:06
To: Chen Liang <chen.l.liang at oracle.com>, classfile-api-dev at openjdk.org <classfile-api-dev at openjdk.org>
Subject: RE: [External] : are CodeElements unique?
How about only for the original, immutable elementlist prior to any transforms?

Also, not sure what you meant by a (index, element) pair.

Thanks, Mark

From: Chen Liang <chen.l.liang at oracle.com<mailto:chen.l.liang at oracle.com>>
Sent: Wednesday, May 7, 2025 11:03 AM
To: Mark Roberts <markro at cs.washington.edu<mailto:markro at cs.washington.edu>>; classfile-api-dev at openjdk.org<mailto:classfile-api-dev at openjdk.org>
Subject: Re: [External] : are CodeElements unique?

Hi Mark,
Very good question - and the answer is unfortunately, no. Transforms are allowed to reuse code models, and I think the bound Code attribute expansion also returns duplicate load or store instructions.
To ensure identity, I think tracking a pair of (index, element) is better.

Regards,
Chen Liang
________________________________
From: Mark Roberts <markro at cs.washington.edu<mailto:markro at cs.washington.edu>>
Sent: Wednesday, May 7, 2025 12:43 PM
To: classfile-api-dev at openjdk.org<mailto:classfile-api-dev at openjdk.org> <classfile-api-dev at openjdk.org<mailto:classfile-api-dev at openjdk.org>>
Cc: Chen Liang <chen.l.liang at oracle.com<mailto:chen.l.liang at oracle.com>>
Subject: [External] : are CodeElements unique?


Are the members of a CodeModel.elementList() unique?  Specifically, is it safe to use a CodeElement as the key value in a Map?



Thank you,

Mark


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