RFR(XS): 8168662: Intrinsic support for event based tracing needs explicit control dependency

[Markus Gronlund]

Greetings,

 

I recently integrated intrinsic support for event based tracing which was tracked in JDK-8166806 (https://bugs.openjdk.java.net/browse/JDK-8166806 ). 

Unfortunately, the changes for 8166806 led to issues seen in testing on SPARC and AARCH64 platforms in that the intrinsic code was missing an explicit control dependency for C2. On the x86 platform, it seems that there is an implicit control dependency that makes the original code work correctly - but on the former platforms, the lack of dependency allows a load to "float" up before the implicit null check dispatch for the uncommon trap.

 

Bug: https://bugs.openjdk.java.net/browse/JDK-8168662 

Webrev: http://cr.openjdk.java.net/~mgronlun/8168662/webrev01/ 

 

I have managed to reproduce and analyze the assembler output for SPARC with the updated changes (please see bug for details).

 

I would need to integrate this to resolve some testing issues, so reviews very much appreciated.

 

Thanks in advance and sorry for any inconveniences related to 8166806.

 

Best regards

Markus

 

PS also thanks for Nils Eliasson for assistance on this issue.

 
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