[lworld] Move null check from method entry into i2c adapter (original) (raw)

Tobias Hartmann tobias.hartmann at oracle.com
Tue May 29 13:01:21 UTC 2018

Hi Roland,

thanks for looking at this!

On 29.05.2018 11:55, Roland Westrelin wrote:

http://cr.openjdk.java.net/~thartmann/valhalla/lworld/adapternullcheck/ That was fast! How is the change in sharedRuntime.cpp related to the null check change?

In lworld, we don't use Q in the signature anymore but need to check the actual type to see if it's a value type. As a result, the code that created the "extended signature" for the calling convention is broken because ss.type() == T_VALUETYPE will always return false. The value types attribute [1] ensures that value type classes are loaded eagerly and we can rely on that when creating the adapters. There's some other dead code that we should fix once we re-enable the calling convention optimization.

We could still have a null literal in the code so checks for non null arguments and an unconditional deoptimization is required.

Yes, my bad. In the meantime I've also hit this problem with a slight modification to our tests. Will send a fixed webrev tomorrow.

Another related change to move null checks out of the common path would be to null check return values in the callee rather than the caller and then deoptimize the caller if it is compiled. That would require a runtime check in the interpreter but in new code we would statically know that a value being returned is not null and so would have no check (unless the value returned is a null literal).

Yes, I think we've discussed this before. It's already on my todo list.

Thanks, Tobias

http://hg.openjdk.java.net/valhalla/valhalla/rev/951b87a3f2c2

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