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

[Fei Gao]

// 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

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

Commit messages:
 - 8289422: Fix and re-enable vector conditional move

Changes: https://git.openjdk.org/jdk/pull/9652/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9652&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8289422
  Stats: 290 lines in 9 files changed: 275 ins; 7 del; 8 mod
  Patch: https://git.openjdk.org/jdk/pull/9652.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9652/head:pull/9652

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