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Missed optimization: Array shadowed in same scope of declaration unnecessarily copied. #72313

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PrototypeNM1 opened this issue May 18, 2020 · 3 comments
Open

Missed optimization: Array shadowed in same scope of declaration unnecessarily copied. #72313

PrototypeNM1 opened this issue May 18, 2020 · 3 comments
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A-mir-opt Area: MIR optimizations A-mir-opt-nrvo Fixed by the Named Return Value Opt. (NRVO) C-enhancement Category: An issue proposing an enhancement or a PR with one. C-optimization Category: An issue highlighting optimization opportunities or PRs implementing such E-needs-mcve Call for participation: This issue has a repro, but needs a Minimal Complete and Verifiable Example I-slow Issue: Problems and improvements with respect to performance of generated code. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.

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@PrototypeNM1
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PrototypeNM1 commented May 18, 2020 •
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Edit: initial attempt at reducing the scope led to an incorrect example, updating with the motivating example.

https://rust.godbolt.org/z/g4imX-

The above shadow on line 119 let position_deltas = position_deltas; results in a series of vmovups, but should be optimized to a noop.
@jonas-schievink jonas-schievink added A-mir-opt-nrvo Fixed by the Named Return Value Opt. (NRVO) C-enhancement Category: An issue proposing an enhancement or a PR with one. E-needs-mcve Call for participation: This issue has a repro, but needs a Minimal Complete and Verifiable Example I-slow Issue: Problems and improvements with respect to performance of generated code. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. A-mir-opt Area: MIR optimizations labels May 18, 2020
@workingjubilee workingjubilee added the C-optimization Category: An issue highlighting optimization opportunities or PRs implementing such label Oct 8, 2023
@moxian
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moxian commented Mar 25, 2025

Fixed by #72205.
Mildly ironic, since that PR was already in flight by the time this issue was submitted, but it took us 5 years to figure this out

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moxian commented Mar 25, 2025

I don't think i have the perms, but let me try...

@rustbot close

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A-mir-opt Area: MIR optimizations A-mir-opt-nrvo Fixed by the Named Return Value Opt. (NRVO) C-enhancement Category: An issue proposing an enhancement or a PR with one. C-optimization Category: An issue highlighting optimization opportunities or PRs implementing such E-needs-mcve Call for participation: This issue has a repro, but needs a Minimal Complete and Verifiable Example I-slow Issue: Problems and improvements with respect to performance of generated code. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.
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@jonas-schievink @PrototypeNM1 @moxian @workingjubilee @rustbot