[aarch64-port-dev ] RFR(S): 8243155: AArch64: Add support for SqrtVF

[Yang Zhang]

Hi,

Could you please help to review this patch?

JBS: https://bugs.openjdk.java.net/browse/JDK-8243155
Webrev: http://cr.openjdk.java.net/~yzhang/8243155/webrev.00/

In Java, Math.sqrt() supports double data only. To support Math.sqrt()
for float, the following conversion must be done.

    float a, b;
    a = (float)Math.sqrt((double)b)

Both AArch64 and x86 support such single-precision sqrt by hardware
instructions. AArch64 FSQRT instruction matches Java (float)Math.
sqrt((double)b) exactly. And X86 has supported vectorization of
Math.sqrt() on floats in [1].

In this patch, vectorized sqrt for float (SqrtVF) is supported in
AArch64 backend. Jtreg test cases for SqrtVF and SqrtVD are also
added. Special cases such as min/max, +/-Inf, +0.0/-0.0 and NaN are
covered.

Testing:
Full jtreg
Newly added sqrt jtreg tests
Panama/Vector API tests which cover vector sqrt

Test case for sqrtvf:

public static void sqrtvf(float[] a, float[] b, float[] c) {
    float tmp;
    for (int i = 0; i < a.length; i++) {
        tmp = (float)(a[i] + b[i]);
        c[i] = (float)Math.sqrt((double)tmp);
    }
}

With this patch, the following code snippet is generated.

  0x0000ffffacaf872c:   ldr	q17, [x18, #16]
  0x0000ffffacaf8730:   ldr	q16, [x16, #16]
  0x0000ffffacaf8734:   fadd	v16.4s, v16.4s, v17.4s
  0x0000ffffacaf8738:   fsqrt	v16.4s, v16.4s
  0x0000ffffacaf8740:   str	q16, [x14, #16]

Performance:
JMH test is attached in JBS.

Before:
Benchmark                (size)  Mode  Cnt  Score   Error  Units
TestVect.testVectSqrtVF    1024  avgt    5  4.372 ± 0.016  us/op

After:
Benchmark                (size)  Mode  Cnt  Score   Error  Units
TestVect.testVectSqrtVF    1024  avgt    5  1.115 ± 0.013  us/op

[1] https://bugs.openjdk.java.net/browse/JDK-8190800

Regards
Yang