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rustc fails to perform LICM in simple code

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.

#145226 In rust-lang/rust;

· SludgePhD opened on Aug 10, 2025

less-than ideal representation for enums that contain a large element with multiple niches

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

A-layoutArea: Memory layout of typesArea: Memory layout of types

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.

#145128 In rust-lang/rust;

· lolbinarycat opened on Aug 8, 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

Inline assembly inhibits emitting <code>nounwind</code>

A-inline-assemblyArea: Inline assembly (`asm!(…)`)Area: Inline assembly (`asm!(…)`)

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

llvm-fixed-upstreamIssue expected to be fixed by the next major LLVM upgrade, or backported fixesIssue expected to be fixed by the next major LLVM upgrade, or backported fixes

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.

#144518 In rust-lang/rust;

· quaternic opened on Jul 26, 2025

Niched option check not optimized out

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.

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.

Status: Open.

#144329 In rust-lang/rust;

· DaniPopes opened on Jul 22, 2025

Missed optimization for format whose argument is a known static string

A-fmtArea: `core::fmt`Area: `core::fmt`

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.

#144328 In rust-lang/rust;

· jrose-signal opened on Jul 22, 2025

select_nth_unstable (partition_at_index) has plenty of redundant bounds checks

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

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.

#144326 In rust-lang/rust;

· kornelski opened on Jul 22, 2025

Iterator stack allocation is not split up

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

Status: Open.

#144306 In rust-lang/rust;

· DaniPopes opened on Jul 22, 2025

Different codegen between comparison of <code>&amp;str</code> and <code>&amp;[u8]</code> on <code>And</code> and <code>Or</code> condition

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.

#144279 In rust-lang/rust;

· CrazyboyQCD opened on Jul 22, 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

Possibly missed optimizations with strided slice access autovectorization

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

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.

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.

#144005 In rust-lang/rust;

· okaneco opened on Jul 16, 2025