RFR: 8276453: Undefined behavior in C1 LIR_OprDesc causes SEGV in fastdebug build [v5]

[Man Cao]

On Wed, 3 Nov 2021 20:01:37 GMT, Man Cao <manc at openjdk.org> wrote:

>> Hi all,
>> 
>> Could anyone provide some feedback on this bug fix and refactoring change? See https://bugs.openjdk.java.net/browse/JDK-8276453 for more details.
>> If the direction of this change looks good, we can proceed removing the "UGLY HACK" in c1_LIR.hpp and refactor occurrences of "opr->fn()" to "opr.fn()".
>
> Man Cao has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix aarch64 and arm builds

I uploaded benchmark results to https://bugs.openjdk.java.net/browse/JDK-8276453. It is over 20 trials. There is no observable difference.
The most relevant metric is "Total Time in Compilation", which is the value of the hsperfdata counter java.ci.totalTime. It includes time spent in both C1 and C2.
Let me know if you also need the logs from +LogCompilation. I have them but they are extremely large (900MiB after 7zip for 20 trials).

I'll work on changing LIR_Opr() to LIR_Opr::nullOpr() and splitting it up, as it also makes sense that the smaller patch should be backported to JDK 11 and 17.

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PR: https://git.openjdk.java.net/jdk/pull/6221