Performance regression with get_many_mut()
#128214
Labels
C-optimization
Category: An issue highlighting optimization opportunities or PRs implementing such
I-heavy
Issue: Problems and improvements with respect to binary size of generated code.
I-slow
Issue: Problems and improvements with respect to performance of generated code.
P-medium
Medium priority
perf-regression
Performance regression.
regression-from-stable-to-stable
Performance or correctness regression from one stable version to another.
Milestone
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In the process of trying to stabilize
get_many_mut()
, and while trying to check what will be the costs of a more detailed error type, I came across the following perf regression from stable to beta.Code
I tried this code:
On stable (with
RUSTC_BOOTSTRAP=1
) this optimizes nicely to the following code (https://godbolt.org/z/zq8EG7df7):However, on beta (and nightly) this adds a whole bunch of unnecessary instructions:
With
cargo-bisect-rustc
I bisected it to #126578. CC @scottmcm.@rustbot label +regression-from-stable-to-beta -regression-untriaged -C-bug +perf-regression +I-heavy +I-slow
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