Cache const-eval local layouts per instance - #161481
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Repeated calls to the same monomorphic const fn re-computed each local's layout because the per-frame cell starts empty. Cache layouts by (Instance, Option<Promoted>) so later invocations skip instantiate and layout_of.
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Thanks for the pull request, and welcome! The Rust Project has assigned @RalfJung (or someone else) to review your changes, you should hear from them (or someone else) within the next two weeks. Please see the contribution instructions and our LLM policy for more information. |
Cell::set does not need a mutable locals binding, and rustc treats warnings as errors in this crate.
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Updating pr description. Sorry for the confusion! |
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Repeated calls to the same monomorphic
const fncurrently re-compute the layout of every local on each invocation:LocalState::layoutis a per-frame cell and starts empty when the frame is pushed.This adds a per-interpreter cache keyed by instance and optional promoted index. The first call fills it; later calls prefill the frame cells and skip instantiate +
layout_of.This is the remaining miss after the per-interpreter type layout cache (#157275). Large
consttables that call small helpers (f64::from_bits, outlined math) currently hitlayout_of_localonce per call instead of once per instance — see #157010 (image,moxcms/pxfm).Local same-commit stage1 measurements (
--edition=2024 --crate-type=bin --emit=metadata, median of 3 after warmup):update_sumtable, N=2^16update_sumtable, N=2^18f64::from_bitshelper × 3 × 2^17The leftover outlined-vs-inlined gap is interpreter call overhead, not layout. The cache removes the redundant
layout_of_localwork described in #157010.Not stacked on #161477. Different subsystem (CTFE layouts, not next-solver fulfillment).
r? RalfJung