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Redundant memory stores with mut parameters in by-value returns

A-ABIArea: Concerning the application binary interface (ABI)Area: Concerning the application binary interface (ABI)

A-codegenArea: Code generationArea: Code generation

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

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.

#149762 In rust-lang/rust;

· andy091203 opened on Dec 8, 2025

Optimization of deinitialization became worse in nightly

A-codegenArea: Code generationArea: Code generation

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

regression-from-stable-to-nightlyPerformance or correctness regression from stable to nightly.Performance or correctness regression from stable to nightly.

S-has-bisectionStatus: A bisection has been found for this issueStatus: A bisection has been found for this issue

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.

#149727 In rust-lang/rust;

· theemathas opened on Dec 7, 2025

Array indexed by exhaustive match still generates bounds checks

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

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-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.

#149480 In rust-lang/rust;

· Arnavion opened on Nov 30, 2025

Nested pattern matching on an enum with niche optimization generates multiple switches

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

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.

#149333 In rust-lang/rust;

· trha opened on Nov 25, 2025

Using array references instead of slices can hurt performance

A-codegenArea: Code generationArea: Code generation

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.

#149293 In rust-lang/rust;

· mwlon opened on Nov 24, 2025

<code>#[derive(Debug)]</code> is introducing potentially panicking code

A-macrosArea: All kinds of macros (custom derive, macro_rules!, proc macros, ..)Area: All kinds of macros (custom derive, macro_rules!, proc macros, ..)

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

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.

#149286 In rust-lang/rust;

· ZhekaS opened on Nov 24, 2025

LLVM not optimizing out heap allocations when using a custom allocator

A-allocatorsArea: Custom and system allocatorsArea: Custom and system allocators

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.

T-opsemRelevant to the opsem teamRelevant to the opsem team

Status: Open.

#149230 In rust-lang/rust;

· izagawd opened on Nov 23, 2025

codegen-units=1 + LTO causes 3-5% performance regression for sequential 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.

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

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

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.

#148670 In rust-lang/rust;

· naoNao89 opened on Nov 7, 2025

Missing niche optimization in non-trivial enum

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

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.

#148566 In rust-lang/rust;

· dragostis opened on Nov 6, 2025

Bad codegen with inlined functions returning <code>Result</code> with a niche.

A-codegenArea: Code generationArea: Code generation

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

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.

Status: Open.

#148461 In rust-lang/rust;

· ruriww opened on Nov 4, 2025

Redundant length check needed to optimize out panicking bounds check in loop

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

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

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.

#147953 In rust-lang/rust;

· okaneco opened on Oct 21, 2025

Redundant bounds check when indexing array with enum in Rust 1.90

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

P-mediumMedium priorityMedium priority

regression-from-stable-to-stablePerformance or correctness regression from one stable version to another.Performance or correctness regression from one stable version to another.

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.

#147831 In rust-lang/rust;

· ictrobot opened on Oct 17, 2025