RFR: 8289422: Fix and re-enable vector conditional move [v5]

[Fei Gao]

On Mon, 26 Sep 2022 20:42:15 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

>> Fei Gao has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains eight commits:
>> 
>>  - Add more tests for swapped inputs where negation happens
>>  - Merge branch 'master' into fg8289422
>>  - Rebase the patch to the latest JDK and add some testcase for NE and EQ
>>    
>>    Change-Id: Ifb02b5efc2a09e6e0b4fc1c8346698597464f448
>>  - Merge branch 'master' into fg8289422
>>    
>>    Change-Id: I09677cb07f6b2717aa768a830663ca455806b900
>>  - Merge branch 'master' into fg8289422
>>    
>>    Change-Id: I870c7bbc73d12bac16756226125edc1a229ba412
>>  - Enable the test only on aarch64 platform because X86 supports vector cmove only on some 256-bits AVXs
>>    
>>    Change-Id: I64dd49380fe3d303ef6be21460df3be31c1458f8
>>  - Merge branch 'master' into fg8289422
>>    
>>    Change-Id: I7936552df6ac12949ed8b550576f4e3520596423
>>  - 8289422: Fix and re-enable vector conditional move
>>    
>>    ```
>>    // float[] a, float[] b, float[] c;
>>    for (int i = 0; i < a.length; i++) {
>>        c[i] = (a[i] > b[i]) ? a[i] : b[i];
>>    }
>>    ```
>>    
>>    After JDK-8139340 and JDK-8192846, we hope to vectorize the case
>>    above by enabling -XX:+UseCMoveUnconditionally and -XX:+UseVectorCmov.
>>    But the transformation here[1] is going to optimize the BoolNode
>>    with constant input to a constant and break the design logic of
>>    cmove vector node[2]. We can't prevent all GVN transformation to
>>    the BoolNode before matcher, so the patch keeps the condition input
>>    as a constant while creating a cmove vector node, and then
>>    restructures it into a binary tree before matching.
>>    
>>    When the input order of original cmp node is different from the
>>    input order of original cmove node, like:
>>    ```
>>    // float[] a, float[] b, float[] c;
>>    for (int i = 0; i < a.length; i++) {
>>        c[i] = (a[i] < b[i]) ? a[i] : b[i];
>>    }
>>    ```
>>    the patch negates the mask of the BoolNode before creating the
>>    cmove vector node in SuperWord::output().
>>    
>>    We can also use VectorNode::implemented() to consult if vector
>>    conditional move is supported in the backend. So, the patch cleans
>>    the related code in SuperWord::implemented().
>>    
>>    With the patch, the performance uplift is:
>>    (The micro-benchmark functions are included in the file
>>    test/micro/org/openjdk/bench/vm/compiler/TypeVectorOperations.java)
>>    
>>    AArch64:
>>    Benchmark (length)  Mode  Cnt   uplift(ns/op)
>>    cmoveD     523      avgt  15    68.89%
>>    cmoveF     523      avgt  15    72.40%
>>    
>>    X86:
>>    Benchmark (length)  Mode  Cnt   uplift(ns/op)
>>    cmoveD     523      avgt  15    73.12%
>>    cmoveF     523      avgt  15    85.45%
>>    
>>    [1]https://github.com/openjdk/jdk/blob/779b4e1d1959bc15a27492b7e2b951678e39cca8/src/hotspot/share/opto/subnode.cpp#L1310
>>    [2]https://github.com/openjdk/jdk/blob/779b4e1d1959bc15a27492b7e2b951678e39cca8/src/hotspot/share/opto/matcher.cpp#L2365
>>    
>>    Change-Id: If046dd745024deb0e602bf7efc2a07c22b89c690
>
> Testing passed.

Thanks for your test work @vnkozlov .

Also thanks all for your review and comments. I'll integrate it.

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

PR: https://git.openjdk.org/jdk/pull/9652