Integrated: 8289422: Fix and re-enable vector conditional move

[Fei Gao]

On Wed, 27 Jul 2022 06:15:57 GMT, Fei Gao <fgao at openjdk.org> wrote:

> // 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](https://bugs.openjdk.org/browse/JDK-8139340) and [JDK-8192846](https://bugs.openjdk.org/browse/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

This pull request has now been integrated.

Changeset: aa48705d
Author:    Fei Gao <fgao at openjdk.org>
Committer: Pengfei Li <pli at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/aa48705dddee674baa479f5128cfc3b426d87d2d
Stats:     381 lines in 7 files changed: 366 ins; 7 del; 8 mod

8289422: Fix and re-enable vector conditional move

Reviewed-by: thartmann, kvn

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

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