RFR: 8244926: Add absolute check for int/long to generate Abs nodes

[Yang Zhang]

Hi,

May I have a review of this enhancement of absolute check for int/long?

JBS: https://bugs.openjdk.java.net/browse/JDK-8244926
Webrev: http://cr.openjdk.java.net/~yzhang/8244926/webrev.00/
 
There is absolute value check for float/double already [1]. In this
patch, absolute value check for integer/long is added. The following
patterns can be matched to AbsI/L nodes:
((a < 0) ? -a : a)
((a <= 0) ? -a : a)
((a > 0) ? a : -a)
((a >= 0) ? a : -a)

Test case:
public static int absi(int a) {
    return ((a < 0) ? -a : a);
}

With c2, AbsI node is generated and matched. The following snippet is
generated on x86:
  0x00007f67c8b6155b:   mov    %ecx,%r11d
  0x00007f67c8b6155e:   sar    $0x1f,%r11d
  0x00007f67c8b61562:   mov    %ecx,%r10d
  0x00007f67c8b61565:   xor    %r11d,%r10d
  0x00007f67c8b61568:   sub    %r11d,%r10d

On AArch64:
  0x0000ffffa8b878e4:   cmp	w3, wzr
  0x0000ffffa8b878e8:   cneg	w17, w3, lt  // lt = tstop

Note: AArch64 result is based on this patch which is in review [2].

Test:
Full jtreg on x86 and AArch64, no new failure

Performance:
Jmh test is uploaded.
http://cr.openjdk.java.net/~yzhang/8244926/TestScalar.java

X86
Before:
Benchmark             (size)  Mode  Cnt     Score   Error  Units
TestScalar.testAbsI1    1024  avgt   25  2648.235 ± 0.810  us/op
TestScalar.testAbsI2    1024  avgt   25  2647.702 ± 0.431  us/op
TestScalar.testAbsI3    1024  avgt   25  2647.605 ± 0.346  us/op
TestScalar.testAbsI4    1024  avgt   25  2647.574 ± 0.651  us/op
TestScalar.testAbsL1    1024  avgt   25  3165.787 ± 0.976  us/op
TestScalar.testAbsL2    1024  avgt   25  3166.582 ± 2.217  us/op
TestScalar.testAbsL3    1024  avgt   25  3168.097 ± 4.071  us/op
TestScalar.testAbsL4    1024  avgt   25  3167.222 ± 2.573  us/op

After:
Benchmark             (size)  Mode  Cnt     Score   Error  Units
TestScalar.testAbsI1    1024  avgt   25  2264.637 ± 1.164  us/op
TestScalar.testAbsI2    1024  avgt   25  2264.318 ± 0.427  us/op
TestScalar.testAbsI3    1024  avgt   25  2264.998 ± 0.903  us/op
TestScalar.testAbsI4    1024  avgt   25  2264.602 ± 0.625  us/op
TestScalar.testAbsL1    1024  avgt   25  2376.513 ± 0.345  us/op
TestScalar.testAbsL2    1024  avgt   25  2376.681 ± 0.565  us/op
TestScalar.testAbsL3    1024  avgt   25  2377.012 ± 0.643  us/op
TestScalar.testAbsL4    1024  avgt   25  2376.921 ± 0.699  us/op

AArch64:
Before:
Benchmark             (size)  Mode  Cnt     Score   Error  Units
TestScalar.testAbsI1    1024  avgt   25  1858.831 ± 1.249  us/op
TestScalar.testAbsI2    1024  avgt   25  1860.248 ± 1.365  us/op
TestScalar.testAbsI3    1024  avgt   25  1859.571 ± 1.177  us/op
TestScalar.testAbsI4    1024  avgt   25  1859.970 ± 0.882  us/op
TestScalar.testAbsL1    1024  avgt   25  1871.520 ± 2.592  us/op
TestScalar.testAbsL2    1024  avgt   25  1872.728 ± 2.301  us/op
TestScalar.testAbsL3    1024  avgt   25  1872.852 ± 2.455  us/op
TestScalar.testAbsL4    1024  avgt   25  1872.720 ± 2.652  us/op

After:
Benchmark             (size)  Mode  Cnt     Score   Error  Units
TestScalar.testAbsI1    1024  avgt   25  1422.781 ± 1.788  us/op
TestScalar.testAbsI2    1024  avgt   25  1423.778 ± 2.612  us/op
TestScalar.testAbsI3    1024  avgt   25  1424.327 ± 2.065  us/op
TestScalar.testAbsI4    1024  avgt   25  1423.269 ± 1.437  us/op
TestScalar.testAbsL1    1024  avgt   25  1434.279 ± 2.312  us/op
TestScalar.testAbsL2    1024  avgt   25  1433.900 ± 2.341  us/op
TestScalar.testAbsL3    1024  avgt   25  1435.967 ± 2.270  us/op
TestScalar.testAbsL4    1024  avgt   25  1437.495 ± 0.957  us/op

[1] http://hg.openjdk.java.net/jdk/jdk/file/dd652a1b2a39/src/hotspot/share/opto/cfgnode.cpp#l1519
[2] https://mail.openjdk.java.net/pipermail/aarch64-port-dev/2020-May/008861.html


Regards,
Yang