RFR: 8290249: Vectorize signum on AArch64 [v4]

[Bhavana-Kilambi]

> This patch auto-vectorizes Math.signum intrinsic for float and  double
> types on aarch64 (Neon and SVE). On SVE supporting machines, if the
> MaxVectorSize <=16 the Neon code would be emitted and if the
> MaxVectorSize > 16, the SVE code for the intrinsic would be emitted.
> 
> Following is the performance data for the micro test here -
> test/micro/org/openjdk/bench/vm/compiler/VectorSignum.java
> 
> 
> Benchmark	                Size    A	B       C
> VectorSignum.doubleSignum	256	1.79	1.70	3.18
> VectorSignum.doubleSignum	512	1.86	1.73	3.69
> VectorSignum.doubleSignum	1024	1.89	1.74	2.98
> VectorSignum.doubleSignum	2048	1.92	1.75	3.04
> VectorSignum.floatSignum	256	3.34	3.06	3.92
> VectorSignum.floatSignum	512	3.63	3.22	5.27
> VectorSignum.floatSignum	1024	3.76	3.35	4.77
> VectorSignum.floatSignum	2048	3.85	3.47	5.59
> 
> 
> A, B , C machine descriptions given below -
> A : 128-bit Neon machine
> B : 256-bit SVE machine
> C : 512-bit SVE machine
> 
> The numbers in the table are the gain ratios between the runtime (ns/op)
> of the scalar, non-vectorized intrinsic code and the vectorized version
> of the intrinsic (this patch).

Bhavana-Kilambi has updated the pull request incrementally with one additional commit since the last revision:

  Add parantheses in aarch_assembler.hpp code to fix operator precedence error

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/9807/files
  - new: https://git.openjdk.org/jdk/pull/9807/files/a2f6b178..221405e0

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9807&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9807&range=02-03

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/9807.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9807/head:pull/9807

PR: https://git.openjdk.org/jdk/pull/9807