Hi Rafael,
It's not easy to analyze optimizations with turbolizer, it's intended more
as a compiler developer tool than an end-user tool. Even if you did, you
might be disappointed if the current benchmark is fine and nothing is
eliminated right now, but a future iteration of Turbofan/shaft ends up
eliminating that loop because of some new analysis. In particular, if we
were to detect that structuredClone has no side-effects, we could
theoretically collapse your loop to just execute the last iteration.
You're probably better off using some intrinsics (--allow-natives-syntax)
to ensure that the object escapes, and make sure that it escapes on each
iteration (and then maybe compare that against a loop that does nothing).
For example, you could write
function DoNotOptimize(x) {}
// Prevent DoNotOptimize from optimizing or being inlined.
%NeverOptimize(DoNotOptimize);
...
for (let i = 0; i < n; ++i)
> DoNotOptimize(structuredClone(blob));
>
This would be similar to DoNotOptimize in the google C++ benchmarking
library
<https://github.com/google/benchmark/blob/main/docs/user_guide.md#:~:text=DoNotOptimize(%3Cexpr%3E)%20forces%20the%20result%20of%20%3Cexpr%3E%20to%20be%20stored%20in%20either%20memory%20or%20a%20register.>
.
- Leszek
On Tue, Sep 3, 2024 at 11:24 PM Rafael Gonzaga <w...@rafaelgss.dev> wrote:
> Hi folks!
>
> I'm member of Node.js team and I'm conducting a research on our benchmark
> suite (https://github.com/nodejs/node/tree/main/benchmark).
>
> In our benchmarks, we attempt to avoid the measured block from being
> eliminated by V8 dead-code elimination by making use of a state and
> checking the state after the benchmark run. Example:
> https://github.com/nodejs/node/blob/main/benchmark/blob/clone.js#L24
>
> However, this is an assumption, we do not check if the measured block is
> being eliminated so, the benchmark result will be noop or we are measuring
> it correctly. I tried to run the benchmark with --trace-turbo and analyzing
> it with tools/turbolizer, but I couldn't find a way to identify which
> blocks were removed.
>
> Is there a way to do that? I understand that usually micro-benchmarks are
> far from reliable, but at the moment I don't see how we could make it more
> sophisticated and specific.
>
> Thanks in advance
>
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