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Adding an <code>assert!</code> prevents bounds check elision

C-optimizationCategory: An issue highlighting optimization opportunities or PRs implementing suchCategory: An issue highlighting optimization opportunities or PRs implementing such

E-needs-bisectionCall for participation: This issue needs bisection: https://github.com/rust-lang/cargo-bisect-rustcCall for participation: This issue needs bisection: https://github.com/rust-lang/cargo-bisect-rustc

I-slowIssue: Problems and improvements with respect to performance of generated code.Issue: Problems and improvements with respect to performance of generated code.

T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.Relevant to the compiler team, which will review and decide on the PR/issue.

Status: Open.

#146988 In rust-lang/rust;

· DCNick3 opened on Sep 24, 2025

MIR optimization produces worse code by losing provenance information

A-LLVMArea: Code generation parts specific to LLVM. Both correctness bugs and optimization-related issues.Area: Code generation parts specific to LLVM. Both correctness bugs and optimization-related issues.

A-rust-for-linuxRelevant for the Rust-for-Linux projectRelevant for the Rust-for-Linux project

C-bugCategory: This is a bug.Category: This is a bug.

I-heavyIssue: Problems and improvements with respect to binary size of generated code.Issue: Problems and improvements with respect to binary size of generated code.

I-slowIssue: Problems and improvements with respect to performance of generated code.Issue: Problems and improvements with respect to performance of generated code.

T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.Relevant to the compiler team, which will review and decide on the PR/issue.

Status: Open.

#146844 In rust-lang/rust;

· nbdd0121 opened on Sep 21, 2025

Adding generic incur in penalty?

C-optimizationCategory: An issue highlighting optimization opportunities or PRs implementing suchCategory: An issue highlighting optimization opportunities or PRs implementing such

I-slowIssue: Problems and improvements with respect to performance of generated code.Issue: Problems and improvements with respect to performance of generated code.

T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.Relevant to the compiler team, which will review and decide on the PR/issue.

Status: Open.

#146555 In rust-lang/rust;

· mdbetancourt opened on Sep 14, 2025

4000% performance regression with "-C target-cpu=x86-64-v3" and fat LTO

A-LTOArea: Link-time optimization (LTO)Area: Link-time optimization (LTO)

C-bugCategory: This is a bug.Category: This is a bug.

I-slowIssue: Problems and improvements with respect to performance of generated code.Issue: Problems and improvements with respect to performance of generated code.

needs-triageThis issue may need triage. Remove it if it has been sufficiently triaged.This issue may need triage. Remove it if it has been sufficiently triaged.

Status: Open.

#146497 In rust-lang/rust;

· im-0 opened on Sep 13, 2025

failed deinterleaving autovectorization

A-autovectorizationArea: Autovectorization, which can impact perf or code sizeArea: Autovectorization, which can impact perf or code size

A-iteratorsArea: IteratorsArea: Iterators

C-bugCategory: This is a bug.Category: This is a bug.

I-slowIssue: Problems and improvements with respect to performance of generated code.Issue: Problems and improvements with respect to performance of generated code.

T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.Relevant to the compiler team, which will review and decide on the PR/issue.

Status: Open.

#146336 In rust-lang/rust;

· edwloef opened on Sep 8, 2025

<code>Vec::into_iter().flatten().collect::&lt;Vec&lt;_&gt;&gt;()</code> doesn't reuse allocation

A-iteratorsArea: IteratorsArea: Iterators

C-optimizationCategory: An issue highlighting optimization opportunities or PRs implementing suchCategory: An issue highlighting optimization opportunities or PRs implementing such

I-slowIssue: Problems and improvements with respect to performance of generated code.Issue: Problems and improvements with respect to performance of generated code.

needs-triageThis issue may need triage. Remove it if it has been sufficiently triaged.This issue may need triage. Remove it if it has been sufficiently triaged.

T-libsRelevant to the library team, which will review and decide on the PR/issue.Relevant to the library team, which will review and decide on the PR/issue.

Status: Open.

#146270 In rust-lang/rust;

· nazar-pc opened on Sep 6, 2025

Transitioning to superset enum variant causes unnecessary copy

A-enumArea: Enums (discriminated unions, or more generally ADTs (algebraic data types))Area: Enums (discriminated unions, or more generally ADTs (algebraic data types))

C-optimizationCategory: An issue highlighting optimization opportunities or PRs implementing suchCategory: An issue highlighting optimization opportunities or PRs implementing such

I-slowIssue: Problems and improvements with respect to performance of generated code.Issue: Problems and improvements with respect to performance of generated code.

T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.Relevant to the compiler team, which will review and decide on the PR/issue.

Status: Open.

#146081 In rust-lang/rust;

· erin-desu opened on Sep 1, 2025

Trivial move creates unnecessary copy

C-optimizationCategory: An issue highlighting optimization opportunities or PRs implementing suchCategory: An issue highlighting optimization opportunities or PRs implementing such

I-slowIssue: Problems and improvements with respect to performance of generated code.Issue: Problems and improvements with respect to performance of generated code.

T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.Relevant to the compiler team, which will review and decide on the PR/issue.

Status: Open.

#146056 In rust-lang/rust;

· DaniPopes opened on Aug 31, 2025

Very bad SIMD code generation for simple Euler integration

A-autovectorizationArea: Autovectorization, which can impact perf or code sizeArea: Autovectorization, which can impact perf or code size

A-SIMDArea: SIMD (Single Instruction Multiple Data)Area: SIMD (Single Instruction Multiple Data)

C-bugCategory: This is a bug.Category: This is a bug.

I-slowIssue: Problems and improvements with respect to performance of generated code.Issue: Problems and improvements with respect to performance of generated code.

O-x86_64Target: x86-64 processors (like x86_64-*) (also known as amd64 and x64)Target: x86-64 processors (like x86_64-*) (also known as amd64 and x64)

T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.Relevant to the compiler team, which will review and decide on the PR/issue.

Status: Open.

#145248 In rust-lang/rust;

· SludgePhD opened on Aug 11, 2025

Slice iterator advancement can become unidiomatic, which seems like a performance problem

C-optimizationCategory: An issue highlighting optimization opportunities or PRs implementing suchCategory: An issue highlighting optimization opportunities or PRs implementing such

I-slowIssue: Problems and improvements with respect to performance of generated code.Issue: Problems and improvements with respect to performance of generated code.

needs-triageThis issue may need triage. Remove it if it has been sufficiently triaged.This issue may need triage. Remove it if it has been sufficiently triaged.

Status: Open.

#144684 In rust-lang/rust;

· hsivonen opened on Jul 30, 2025

Range of index variables forgotten in an <code>else if</code>

A-LLVMArea: Code generation parts specific to LLVM. Both correctness bugs and optimization-related issues.Area: Code generation parts specific to LLVM. Both correctness bugs and optimization-related issues.

C-optimizationCategory: An issue highlighting optimization opportunities or PRs implementing suchCategory: An issue highlighting optimization opportunities or PRs implementing such

I-slowIssue: Problems and improvements with respect to performance of generated code.Issue: Problems and improvements with respect to performance of generated code.

needs-triageThis issue may need triage. Remove it if it has been sufficiently triaged.This issue may need triage. Remove it if it has been sufficiently triaged.

Status: Open.

#144522 In rust-lang/rust;

· kornelski opened on Jul 26, 2025

<code>iter_mut</code> is slightly slower than code with a manual for loop

C-optimizationCategory: An issue highlighting optimization opportunities or PRs implementing suchCategory: An issue highlighting optimization opportunities or PRs implementing such

I-slowIssue: Problems and improvements with respect to performance of generated code.Issue: Problems and improvements with respect to performance of generated code.

T-libsRelevant to the library team, which will review and decide on the PR/issue.Relevant to the library team, which will review and decide on the PR/issue.

Status: Open.

#144118 In rust-lang/rust;

· hkBst opened on Jul 18, 2025