RFR: 8303278: Imprecise bottom type of ExtractB/UB

[Eric Liu]

On Mon, 20 Mar 2023 10:24:10 GMT, Tobias Hartmann <thartmann at openjdk.org> wrote:

> This triggers failures in testing:
> 
> ```
> jdk/incubator/vector/Byte64VectorTests.java
> 
> java.lang.Exception: failures: 1
> 	at com.sun.javatest.regtest.agent.TestNGRunner.main(TestNGRunner.java:95)
> 	at com.sun.javatest.regtest.agent.TestNGRunner.main(TestNGRunner.java:53)
> 	at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
> 	at java.base/java.lang.reflect.Method.invoke(Method.java:578)
> 	at com.sun.javatest.regtest.agent.MainWrapper$MainThread.run(MainWrapper.java:125)
> 	at java.base/java.lang.Thread.run(Thread.java:1623)
> ```


I think this should be caused by https://bugs.openjdk.org/browse/JDK-8303508. The removed narrowing exposed this issue on x86, that the generated code of ExtractB perhaps does not handle sign-bit correctly. TBH I'm not familiar with x86 instructions... @jatin-bhateja Could you help to take a look at this bug?

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PR Comment: https://git.openjdk.org/jdk/pull/13070#issuecomment-1477172638