Taproot sig message #3
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There was a question whether this is equally performant. There are multiple good reasons why it should be: 1. `get_or_insert_with` is marked `#[inline]` 2. Any good optimizer will inline a function that is used exactly once 3. 1 and 2 conclude that the closure will get inlined 4. Computing self.tx can then be moved to the only branch where it is required. 5. Even if get_or_insert_with didn't get optimized, which is extremely unlikely, the `tx` field is at the beginning of the struct and it probably has pointer alignment (`Deref` suggests it's a pointer). Alignment larger than pointer is not used, so we can expect the fields to be ordered as-defined. (This is not guaranteed by Rust but there's not good reason to change the order in this case.) We can assume that offset to tx is zero in most cases which means no computation is actually needed so the expression before closure is no-op short of passing it into the closure as an argument. At the time of writing `#[inline]` can be seen at https://doc.rust-lang.org/src/core/option.rs.html#933
This refactors the code to make it possible to use `get_or_insert_with` instead of unwrapping in `segwit_cache()`. To achieve it `common_cache` is refactored into two functions: one taking only the required borrows and the original calling the new one. `segwit_cache` then calls the new function so that borrows are OK. Apart from removing unwrap, this avoids calling `common_cache` multiple times.
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Thinking about it a bit more, if cache miss is very rare we could make the closures |
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I am in PTO at the moment but I did a quick look and I think I am going to merge this. Just I am not doing it now because I need some time to dedicate to this and other comments in the PR... |
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These changes replace
unwrap()withget_or_insert_with()in cache methods. The commits explain why performance shouldn't be lost.