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
