RFR: 8303278: Imprecise bottom type of ExtractB/UB [v2]

[Eric Liu]

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

>> Eric Liu has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains two additional commits since the last revision:
>> 
>>  - Merge jdk:master
>>    
>>    Change-Id: I40cce803da09bae31cd74b86bf93607a08219545
>>  - 8303278: Imprecise bottom type of ExtractB/UB
>>    
>>    This is a trivial patch, which fixes the bottom type of ExtractB/UB
>>    nodes.
>>    
>>    ExtractNode can be generated by Vector API Vector.lane(int), which gets
>>    the lane element at the given index. A more precise type of range can
>>    help to optimize out unnecessary type conversion in some cases.
>>    
>>    Below shows a typical case used ExtractBNode
>>    
>>    ```
>>      public static byte byteLt16() {
>>       ByteVector vecb = ByteVector.broadcast(ByteVector.SPECIES_128, 1);
>>       return vecb.lane(1);
>>      }
>>    
>>    ```
>>    In this case, c2 constructs IR graph like:
>>    
>>        ExtractB  ConI(24)
>>           |     __|
>>           |    /  |
>>        LShiftI  __|
>>           |    /
>>        RShiftI
>>    
>>    which generates AArch64 code:
>>    
>>      movi    v16.16b, #0x1
>>      smov    x11, v16.b[1]
>>      sxtb    w0, w11
>>    
>>    with this patch, this shift pair can be optimized out by RShiftI's
>>    identity [1]. The code is optimized to:
>>    
>>      movi    v16.16b, #0x1
>>      smov    x0, v16.b[1]
>>    
>>    [TEST]
>>    
>>    Full jtreg passed except 4 files on x86:
>>    
>>    jdk/incubator/vector/Byte128VectorTests.java
>>    jdk/incubator/vector/Byte256VectorTests.java
>>    jdk/incubator/vector/Byte512VectorTests.java
>>    jdk/incubator/vector/Byte64VectorTests.java
>>    
>>    They are caused by a known issue on x86 [2].
>>    
>>    [1] https://github.com/openjdk/jdk/blob/742bc041eaba1ff9beb7f5b6d896e4f382b030ea/src/hotspot/share/opto/mulnode.cpp#L1052
>>    [2] https://bugs.openjdk.org/browse/JDK-8303508
>>    
>>    Change-Id: Ibea9aeacb41b4d1c5b2621c7a97494429394b599
>
> 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)

@TobiHartmann  Could you help to take a look?

-------------

PR Comment: https://git.openjdk.org/jdk/pull/13070#issuecomment-1489880736