ilya-biryukov added a comment.
Here are some numbers from running `clang -cc1 -Eonly` on `SemaExpr.cpp`, it
includes a whole ton of headers, including a rather large `TreeTransform.h`.
This was run on my machine, so keep in mind it's rather noisy. Minimal times
should be somewhat representative, though.
Before:
Time (mean ± σ): 159.5 ms ± 7.3 ms [User: 137.3 ms, System: 22.1
ms]
Range (min … max): 148.9 ms … 199.5 ms 100 runs
After (no callback specified):
Time (mean ± σ): 165.0 ms ± 7.5 ms [User: 142.8 ms, System: 22.2
ms]
Range (min … max): 155.0 ms … 196.7 ms 100 runs
And two more measurements with callbacks non-empty callbacks:
Counting tokens:
Time (mean ± σ): 169.0 ms ± 9.5 ms [User: 147.3 ms, System: 21.7
ms]
Range (min … max): 158.3 ms … 206.0 ms 100 runs
Saving tokens to a vector:
Time (mean ± σ): 191.0 ms ± 5.5 ms [User: 154.1 ms, System: 36.8
ms]
Range (min … max): 180.4 ms … 221.0 ms 100 runs
Overall, the performance cost in empty-callback case seems to be lower than
`5%`. This is significant, but hopefully acceptable.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D59885/new/
https://reviews.llvm.org/D59885
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