[9] RFR (S): 8153540: C2 intrinsic for Unsafe.allocateInstance doesn't properly filter out array classes

[Vladimir Kozlov]

 > Unsafe.allocateInstance intrinsic can instantiate arrays, but the allocation logic is broken.

But it should not allocate arrays. Right? This is what your java changes do now.

Should it be allocateInstance0 ?:

+ // public native Object Unsafe.allocateInstance(Class<?> cls);

You removed next stop check. Is it because java code will cat the NULL?:
     Node* cls = null_check(argument(1));
     if (stopped())  return true;

The test misses bug number @bug

Thanks,
Vladimir K

On 4/8/16 9:47 AM, Vladimir Ivanov wrote:
> http://cr.openjdk.java.net/~vlivanov/8153540/webrev.00/hotspot/
> http://cr.openjdk.java.net/~vlivanov/8153540/webrev.00/jdk/
>
> https://bugs.openjdk.java.net/browse/JDK-8153540
>
> Unsafe.allocateInstance intrinsic can instantiate arrays, but the allocation logic is broken.
>
> The proposed fix is to perform necessary checks in Java code before calling the intrinsic.
>
> I did some performance measurements [1] and reflection (non-constant class) case (non-constant class) regressed ~5-10%
> due to new guards added.
>
> I also experimented with a hotspot-only fix [2], but it looks uglier. So, if you consider the regression in reflective
> case non-critical, I'd prefer to go with JDK checks.
>
> Testing: regression test, JPRT, RBT (pit-hs-comp; in progress), microbenchmarks.
>
> Thanks!
>
> Best regards,
> Vladimir Ivanov
>
> [1] http://cr.openjdk.java.net/~vlivanov/8153540/AllocInstance.java
>
> Baseline:
>    AllocInstance.testConstant    avgt   25  3.736 ± 0.054  ns/op
>    AllocInstance.testReflective  avgt   25  5.880 ± 0.080  ns/op
>
> JDK fix:
>    AllocInstance.testConstant    avgt   25  3.959 ± 0.205  ns/op
>    AllocInstance.testReflective  avgt   25  6.274 ± 0.180  ns/op
>
> [2] http://cr.openjdk.java.net/~vlivanov/8153540/webrev.slow_path
>
>    AllocInstance.testConstant avgt 25 3.957 ± 0.159 ns/op
>    AllocInstance.testReflective avgt 25 5.901 ± 0.057 ns/op
>