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From "Sebb (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (BCEL-195) addition of hashCode() to generic/Instruction.java breaks Targeters
Date Tue, 25 Aug 2015 21:05:45 GMT

    [ https://issues.apache.org/jira/browse/BCEL-195?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14711977#comment-14711977
] 

Sebb commented on BCEL-195:
---------------------------

OK, I see.

Do both patches need to be applied still?

But we really need some test code that can potentially expose the problem and test the new
code.

I realise that it's not possible to provide a copy of everything Daikon does, but even a single
sample would help.

Seems to me that there are at least two types of branch changes:
- changing one or more branch instructions to point to a new location
- changing the position of an Instruction handle within the list by adding/removing instructions
earlier in the list

I assume it is the first case that is causing problems.

> 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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