[9] RFR (XS): 8153357: C2 creates incorrect cast after eliminating phi with unique input

[Vladimir Kozlov]

I think check should use !isa_oopptr() since one of nodes could be ConP NULL ptr which is not klassptr.

Thanks,
Vladimir

On 4/14/16 6:21 AM, Zoltán Majó wrote:
> Hi,
>
>
> please review the patch for 8153357.
>
> https://bugs.openjdk.java.net/browse/JDK-8153357
>
> Problem: When determining the unique input of a phi, the C2 compiler removes cast nodes connecting the phi to its unique input.
> http://hg.openjdk.java.net/jdk9/hs-comp/hotspot/file/a76d63163758/src/share/vm/opto/cfgnode.cpp#l1181
>
> Then (if the phi has indeed a unique input), the C2 compiler attempts replace the phi with a cast node. The new cast node feeds from the unique input.
>
> To be able to remove the phi node, the C2 compiler must  to determine the type of cast to add in place of the phi node (CastII, CastPP, or CheckCastPP).
> http://hg.openjdk.java.net/jdk9/hs-comp/hotspot/file/a76d63163758/src/share/vm/opto/cfgnode.cpp#l1705
>
> The failure in the bug report appears because the C2 compiler adds a cast node of unexpected type to the graph (a CheckCastPP instead of a CastPP when casting between two klass pointers).
>
> Please find more details about the cause of the failure in the bug description:
> https://bugs.openjdk.java.net/browse/JDK-8153357?focusedCommentId=13927108&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-13927108
>
>
> Solution: Refine C2's logic to determine the type of cast node added.
>
> Webrev:
> http://cr.openjdk.java.net/~zmajo/8153357/webrev.00/
>
> Testing:
> - JPRT;
> - all hotspot compiler tests with RBT (-Xmixed, -Xcomp);
> - 500 non-failing runs with the reproducer (the problem reproduces with < 100 runs).
>
> Thank you and best regards,
>
>
> Zoltan
>