RFR 8248043: Need to eliminate excessive i2l conversions

[Claes Redestad]

Hi Boris,

this looks like a nice improvement! I just have some comments about the
micro.

I was curious whether the optimization works when the constant is on
the LHS and added a variant of the micro to try that[1]. Results are
interesting (Intel Xeon):

Benchmark                            Mode  Cnt   Score   Error  Units
SkipIntToLongCast.skipCastTest       avgt    5  30.937 ± 0.056  ns/op
SkipIntToLongCast.skipCastTestLeft   avgt    5  30.937 ± 0.140  ns/op

With your patch:
Benchmark                            Mode  Cnt   Score   Error  Units
SkipIntToLongCast.skipCastTest       avgt    5  14.123 ± 0.035  ns/op
SkipIntToLongCast.skipCastTestLeft   avgt    5  17.420 ± 0.044  ns/op

Seems like the optimization is mostly effective, but not getting all
the way. I wouldn't worry about it for this RFE, but perhaps something
to investigate in a follow-up. Feel free to include such a variant in
your patch though (no attribution necessary).

The micro also stabilizes very quickly, so you might want to provide
some default tuning to keep runtime in check, e.g., something like:

@Warmup(iterations = 10, time = 500, timeUnit = TimeUnit.MILLISECONDS)
@Measurement(iterations = 5, time = 1000, timeUnit = TimeUnit.MILLISECONDS)
@Fork(3)

Thanks!

/Claes

[1]
     @Benchmark
     public int skipCastTestLeft() {
         for (int i = 0; i < ARRAYSIZE_L; i++) {
             if (ARRAYSIZE_L == intValues[i]) {
                 return i;
             }
         }
         return 0;
     }

On 2020-06-26 17:05, Boris Ulasevich wrote:
> Hi all,
> 
> Please review the change to eliminate the unnecessary i2l conversion
> for expressions like this: "if (intValue == 1L)".
> 
> http://bugs.openjdk.java.net/browse/JDK-8248043
> http://cr.openjdk.java.net/~bulasevich/8248043/webrev.01
> 
> The provided benchmark shows performance boost on all platforms:
> - Intel Xeon: 32.705 --> 14.234 ns/op
> - arm64: 42.060 --> 25.456 ns/op
> - arm32: 618.763 --> 314.040 ns/op
> - ppc8:  81.218 --> 63.026 ns/op
> 
> Testing done: jtreg, jck.
> 
> thanks,
> Boris