[DRAFT] Rc: allow deduping both deref and clone across types
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How does this relate to #132553? |
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@Victoronz Oh, I didn't even know that existed. Well, taking a look, the difference is that it looks like the codegen test I added here wouldn't pass with that version of the PR, because that still keeps the different offsets from the counts to the value. So that one makes EDIT: updated the title and OP to help make that clearer. |
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Rc: store the pointer to the value, rather than to the allocationRc: allow deduping both deref and clone across types
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The job Click to see the possible cause of the failure (guessed by this bot) |
Noratrieb
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@bors try |
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[DRAFT] `Rc`: allow deduping both `deref` and `clone` across types This works by *always* putting the counts *just* before the value, rather than using an `RcInner` type at all. By doing that, the offset to the counts are exactly the same for all types -- small or large, low alignment or high -- so `Rc::clone` can be polymorphized, and `Rc::deref` is always just a no-op. r? ghost
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☀️ Try build successful - checks-actions |
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@rust-timer build 711b97b |
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Finished benchmarking commit (711b97b): comparison URL. Overall result: ❌✅ regressions and improvements - please read the text belowBenchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. While you can manually mark this PR as fit for rollup, we strongly recommend not doing so since this PR may lead to changes in compiler perf. Next Steps: If you can justify the regressions found in this try perf run, please indicate this with @bors rollup=never Instruction countThis is the most reliable metric that we have; it was used to determine the overall result at the top of this comment. However, even this metric can sometimes exhibit noise.
Max RSS (memory usage)Results (primary -3.0%, secondary 3.5%)This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.
CyclesResults (primary -0.5%, secondary 3.9%)This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.
Binary sizeResults (primary -0.1%, secondary 7.4%)This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.
Bootstrap: 788.599s -> 786.092s (-0.32%) |
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I'm going to close this and hope that @EFanZh's version (see #132553 (comment)) will pick up anything useful that I had here -- realistically I don't think I'll get back to this anytime soon, and they've made a bunch of important progress in theirs (like fixing debug visualizers) that I never did here. |
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This works by always putting the counts just before the value, rather than using an
RcInnertype at all.By doing that, the offset to the counts are exactly the same for all types -- small or large, low alignment or high -- so
Rc::clonecan be polymorphized, andRc::derefis always just a no-op.r? ghost