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

[Vladimir Kozlov]

On Thu, 2 Dec 2021 13:36:26 GMT, Tobias Hartmann <thartmann at openjdk.org> wrote:

>> src/hotspot/share/opto/macro.cpp line 1245:
>> 
>>> 1243:   }
>>> 1244: 
>>> 1245:   if (C->env()->dtrace_alloc_probes() ||
>> 
>> This check was introduced in JDK-6788527.
>> I'm not very clear about the root cause.
>
> @vnkozlov do you remember?

Yes, it replaced `DTraceAllocProbes` flag check with cached value:
https://hg.openjdk.java.net/jdk7u/jdk7u-dev/hotspot/rev/c96bf21b756f

We cached JVMTI and DTrace flags values before compilation and check after compilation to throw it out if flags were changed:
https://hg.openjdk.java.net/jdk7u/jdk7u-dev/hotspot/rev/c96bf21b756f#l8.38

-------------

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