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https://issues.apache.org/jira/browse/BCEL-195?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14710921#comment-14710921
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Sebb commented on BCEL-195:
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I assume that the intention of re-using Instructions is partly to save space,
but also so that BIs with the same target can be updated more easily, as only
one instruction has to be changed. Though another way to do this is of course
to move the IH to a different part of the list.
Changing the design to require use of an Instruction Factory would probably
require substantial changes to user code, so I think should be avoided unless
absolutely essential. In which case, I would start again and make the
Instructions immutable (I'm still not sure it's necessary to be able to change
them). Likewise, I'm not sure the IH cache is a good idea.
As to considerations of memory usage or time: we need to get the code working
properly first.
> addition of hashCode() to generic/Instruction.java breaks Targeters
> -------------------------------------------------------------------
>
> Key: BCEL-195
> URL: https://issues.apache.org/jira/browse/BCEL-195
> Project: Commons BCEL
> Issue Type: Bug
> Components: Main
> Affects Versions: 6.0
> Reporter: Mark Roberts
> Attachments: bcel195.diff, targeters.diff
>
>
> [Revision 1532198|http://svn.apache.org/r1532198] added a {{hashCode()}}
> function to the Instruction class. Unfortunately, this breaks the
> Instruction targeting mechanism. I understand the goal of trying to reuse
> instructions - an 'iadd' is the same as any other 'iadd'. However, one
> 'goto 50' is not the same as another 'goto 50' due to the way Targeters are
> implemented. If branch instructions are reused, then only one entry gets put
> on the Targeter list. So when some api is used to modify the instruction
> list and location 50 becomes location 52 ONLY ONE of the branches gets
> updated. A very bad thing. So unless you modify the hash to special case
> branch instructions (and there might be other instructions needing special
> treatment as well) its broken. We fixed it by simply commenting the hash out
> to make things like they used to be and all works great.
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