[aarch64-port-dev ] RFR: 8240353: AArch64: missing support for -XX:+ExtendedDTraceProbes in C1

[Nick Gasson]

Hi Andrew,

On 03/11/20 22:03 pm, Andrew Haley wrote:
>>
>> I wonder what the actual intent was here, and whether anyone has a use
>> for being able to enable dtrace method probes late.
>
> Thinking some more, ISTM that changing all this code so that it's
> tested at startup rather than runtime doesn't gain us very much and
> potentially closes the door future improvements in this area. I think
> your patch would be smaller and simpler otherwise.
>
> Is the overhead of that test-and-branch significant?

Not really: with a contrived benchmark like the following the overhead
is around 1% when using -Xint.

    public static long ackermann(long m, long n) {
        if (m == 0) return n + 1;
        if (n == 0) return ackermann(m - 1, 1);
        return ackermann(m - 1, ackermann(m, n - 1));
    }

    @Benchmark
    public long manyCalls() {
        return ackermann(3, 6);
    }

Revert that part of the patch?


Nick