On Wed, 4 May 2022 01:59:17 GMT, Quan Anh Mai <d...@openjdk.java.net> wrote:
> 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 > cmovel 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. The changes to `Float` and `Double` look good. I don't think we need additional tests, see test/jdk/java/lang/Math/IeeeRecommendedTests.java. At first i thought we no longer need PR #8459 but it seems both PRs are complimentary, albeit PR #8459 has more modest performance gains for the intrinsics. ------------- PR: https://git.openjdk.java.net/jdk/pull/8525
