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<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

zip(chain(...)) with iterators optimizes very poorly

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.

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-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.

#143966 In rust-lang/rust;

· The-personified-devil opened on Jul 15, 2025

Conditional <code>char</code> counter not recognized as never-overflowing

A-sliceArea: `[T]`Area: `[T]`

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.

#143959 In rust-lang/rust;

· Rudxain opened on Jul 15, 2025

Store resolutions for associated type constraints instead of recomputing them

A-resolveArea: Name/path resolution done by `rustc_resolve` specificallyArea: Name/path resolution done by `rustc_resolve` specifically

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.

#143945 In rust-lang/rust;

· Kobzol opened on Jul 14, 2025

Attributes are parsed twice

A-attributesArea: Attributes (`#[…]`, `#![…]`)Area: Attributes (`#[…]`, `#![…]`)

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.

#143940 In rust-lang/rust;

· JonathanBrouwer opened on Jul 14, 2025

Nested arrays are completely loop-unrolled into a huge amount of instructions (feat. 153 MB binary)

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

Status: Open.

#143673 In rust-lang/rust;

· theemathas opened on Jul 9, 2025

<code>vec![[[[0i32; 16]; 16]; 16]; 0]</code> is not optimized

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

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.

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.

#143637 In rust-lang/rust;

· theemathas opened on Jul 8, 2025

Regression in inlining performance from 1.82.0

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.

#143513 In rust-lang/rust;

· Guilucand opened on Jul 5, 2025

Call to <code>needs_drop</code> doesn't optimize properly in combination with unrelated mutation of static variable

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

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.

#143320 In rust-lang/rust;

· laurmaedje opened on Jul 2, 2025

<code>opt-level=s</code> doesn't enable the SLP vectorizer (fails to use packed floats)

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.

#143242 In rust-lang/rust;

· lhecker opened on Jun 30, 2025

Bounds check not elided for <code>slice::split_at</code> after loop

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.

#143027 In rust-lang/rust;

· okaneco opened on Jun 25, 2025