RFR: 8278079: C2: expand_dtrace_alloc_probe doesn't take effect in macro.cpp

[Denghui Dong]

On Thu, 2 Dec 2021 15:03:43 GMT, Tobias Hartmann <thartmann at openjdk.org> wrote:

> Yes but that check is useless if the compilation does not even use the flag, right?

Hmmm... I may not get your points.

According to JDK-6788527 and the related patch:

> Jvmti and DTrace threads may change global flags used by Compiler
in the middle of compilation. These leads to inconsistent answers
from MethodLiveness which leads to the failure during parsing.
It also invalidates dependencies constructed during compilation.

I think that explains why ciEnv need to cache DTrace flags before compilation, and _dtrace_method_probes/_dtrace_alloc_probes is set enabled if ExtendedDTraceProbes is true, so I think ExtendedDTraceProbes may still be useful, right?

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PR: https://git.openjdk.java.net/jdk/pull/6639