RFR: 8285973: x86_64: Improve fp comparison and cmove for eq/ne

[Quan Anh Mai]

Hi,

This patch optimises the matching rules for floating-point comparison with respects to eq/ne on x86-64

1, When the inputs of a comparison is the same (i.e `isNaN` patterns), `ZF` is always set, so we don't need `cmpOpUCF2` for the eq/ne cases, which improves the sequence of `If (CmpF x x) (Bool ne)` from

    ucomiss xmm0, xmm0
    jp      label
    jne     label

into

    ucomiss xmm0, xmm0
    jp      label

2, The move rules for `cmpOpUCF2` is missing, which makes patterns such as `x == y ? 1 : 0` to fall back to `cmpOpU`, which have a really high cost of fixing the flags, such as

        xorl    ecx, ecx
        ucomiss xmm0, xmm1
        jnp     done
        pushf
        andq    [rsp], 0xffffff2b
        popf
    done:
        movl    eax, 1
        cmovenl eax, ecx

The patch changes this sequence into

    xorl    ecx, ecx
    ucomiss xmm0, xmm1
    movl    eax, 1
    cmovpl  eax, ecx
    cmovnel eax, ecx

3, The patch also changes the pattern of `isInfinite` to be more optimised by using `Math.abs` to reduce 1 comparison and compares the result with `MAX_VALUE` since `>` is more optimised than `==` for floating-point types.

The benchmark results are as follow:

    Before:
    Benchmark                      Mode  Cnt     Score     Error  Units
    FPComparison.equalDouble       avgt    5  2876.242 ±  58.875  ns/op
    FPComparison.equalFloat        avgt    5  3062.430 ±  31.371  ns/op
    FPComparison.isFiniteDouble    avgt    5   475.749 ±  19.027  ns/op
    FPComparison.isFiniteFloat     avgt    5   506.525 ±  14.417  ns/op
    FPComparison.isInfiniteDouble  avgt    5  1232.800 ±  31.677  ns/op
    FPComparison.isInfiniteFloat   avgt    5  1234.708 ±  70.239  ns/op
    FPComparison.isNanDouble       avgt    5  2255.847 ±   7.238  ns/op
    FPComparison.isNanFloat        avgt    5  2567.044 ±  36.078  ns/op

    After:
    Benchmark                      Mode  Cnt     Score     Error  Units
    FPComparison.equalDouble       avgt    5   594.636 ±   8.922  ns/op
    FPComparison.equalFloat        avgt    5   663.849 ±   3.656  ns/op
    FPComparison.isFiniteDouble    avgt    5   518.309 ± 107.352  ns/op
    FPComparison.isFiniteFloat     avgt    5   515.576 ±  14.669  ns/op
    FPComparison.isInfiniteDouble  avgt    5   621.185 ±  11.935  ns/op
    FPComparison.isInfiniteFloat   avgt    5   623.566 ±  15.206  ns/op
    FPComparison.isNanDouble       avgt    5   400.124 ±   0.762  ns/op
    FPComparison.isNanFloat        avgt    5   546.486 ±   1.509  ns/op

Thank you very much.

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

Commit messages:
 - fix tests
 - test
 - improve infinity
 - remove expensive rules
 - improve fp comparison

Changes: https://git.openjdk.java.net/jdk/pull/8525/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8525&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8285973
  Stats: 657 lines in 8 files changed: 569 ins; 70 del; 18 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8525.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8525/head:pull/8525

PR: https://git.openjdk.java.net/jdk/pull/8525