[WIP] Perf experiment for rustc-hash with ones-idiom init #122316
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CPUs for a while now know (at least) PCMPEQ as a dependency-breaking "ones idiom", and it's not a huge encoding next to constant loads. Let's try it out and see how the hashing goes.
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rustbot has assigned @Mark-Simulacrum. Use r? to explicitly pick a reviewer |
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doh. |
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@bors try @rust-timer queue |
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…ze-max, r=<try> [WIP] Perf experiment for rustc-hash with ones-idiom init CPUs for a while now know (at least) PCMPEQ as a dependency-breaking "ones idiom", and it's not a huge encoding next to constant loads. Let's try it out and see how the hashing goes. Spurred by rust-lang/rustc-hash#17
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The job Click to see the possible cause of the failure (guessed by this bot) |
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☀️ Try build successful - checks-actions |
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Finished benchmarking commit (5a5b692): comparison URL. Overall result: ❌ regressions - ACTION NEEDEDBenchmarking 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 a highly reliable metric that was used to determine the overall result at the top of this comment.
Max RSS (memory usage)ResultsThis 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.
CyclesResultsThis 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 sizeResultsThis 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: 648.293s -> 647.535s (-0.12%) |
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@nnethercote ...Okay, this is absolutely trash at performance, but I was right that there's no binary size regressions. 🥲 |
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Multiple people have tried and failed to improve |
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@nnethercote Ah, yes, // Dear programmer:
// When I wrote this code, only god and
// I knew how it worked.
// Now, only god knows it!
//
// Therefore, if you are trying to optimize
// this routine and it fails (most surely),
// please increase this counter as a
// warning for the next person:
//
// total hours wasted here = 254
// |
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CPUs for a while now know (at least) PCMPEQ as a dependency-breaking "ones idiom", and it's not a huge encoding next to constant loads. Let's try it out and see how the hashing goes.
Spurred by rust-lang/rustc-hash#17