IdeaWell

Project ideas from Hacker News discussions.

Is Rust faster than C?

Original Article

Hacker News Discussion

📝 Discussion Summary (Click to expand)

Here are the 4 most prevalent themes from the discussion.

1. The Question is Ill-Defined

A recurring theme is that a generic speed comparison between languages is meaningless without defining specific contexts, such as the compiler, the type of code, and the metrics for "fast" (development time vs. execution time).

"the question is malformed, you need to first state what the boundaries are before you can make any conclusions." — steveklabnik

"I think that there are so many variables that it is difficult to draw generalized conclusions." — senko

2. Aliasing and Optimization Opportunities

Many users debated whether Rust's stricter aliasing rules (which are similar to C++'s but enforced by the type system) provide a tangible performance advantage over C.

"Rust should have even more opportunities of this due to restrictions it has for writable references." — Karliss

"I believe this advantage is currently mostly theoretical, as the code ultimately gets compiled with LLVM which does not fully utilize all the additional optimization opportunities." — Tuna-Fish

3. Ease of Parallelism and Correctness

Several comments highlighted that Rust's safety guarantees make it much easier to write parallelized code correctly, potentially leading to faster execution in practice compared to C where concurrency is often avoided due to complexity and risk.

"Mozilla tried to parallelize Firefox’s style layout twice in C++, and both times the project failed. The multithreading was too tricky to get right." — classified

"In Rust, whether you use threads or not, all globals must be thread-safe, and the borrow checker requires memory access to be shared XOR mutable... In C, the cost/benefit analysis is different." — pornel

4. Compile-Time Abstractions vs. Runtime Overhead

The discussion touched on how language features influence performance. Rust's generics (monomorphization) allow for zero-cost abstractions and inlining, whereas C often relies on function pointers (like qsort) which can inhibit optimization.

"In Rust and C++, the standard library sorting functions are templated on the comparison function. This means it's much easier for the compiler to specialize the sorting function, inline the comparisons and optimize around it." — OskarS

"Rust would not have achieved C speeds if it did not carefully pick abstractions that were amenable to optimization." — kibwen

🚀 Project Ideas

RustAliasAnalyzer

Summary

  • Identifies performance-critical areas in Rust codebases where stricter aliasing semantics could theoretically enable compiler optimizations, but are currently unexploited.
  • Generates benchmarks comparing idiomatic Rust with equivalent code using &mut T to signal non-aliasing potential to the compiler.
  • Provides actionable suggestions for code restructuring to maximize aliasing optimization opportunities.

Details

Key Value
Target Audience Rust performance engineers, systems programmers, and compiler contributors.
Core Feature Static analysis to flag unoptimized aliasing patterns and generate LLM/Virtual Rust code for testing optimization potential.
Tech Stack Rust (using rust-analyzer libraries), LLVM analysis tools, simple web UI (React/Vite).
Difficulty Medium
Monetization Revenue-ready: SaaS subscription for enterprise codebases, one-time fee for individual project analysis.

Notes

  • Addresses the direct user need for concrete examples: teo_zero: "Interesting concept! Any examples?" and Karliss: "Not exactly real world, but real code example demonstrating strict aliasing rule in action...".
  • HN commenters are deeply technical and would appreciate tooling that bridges the gap between theory and practice regarding aliasing, a topic explicitly discussed by steveklabnik and gignico.
  • The tool solves the frustration of manually inspecting assembly for optimization differences, which taminka suggests doing manually ("profile stuff and compare outputted assembly").

CompileTimeTracker

Summary

  • Tracks and visualizes Rust compilation times, specifically isolating the overhead introduced by generic monomorphization and trait usage.
  • Correlates compilation time spikes with specific code changes (e.g., adding a new generic constraint) to help developers understand the "cost" of zero-cost abstractions.
  • Offers recommendations for reducing compile times without sacrificing runtime performance (e.g., suggesting dyn traits where appropriate).

Details

Key Value
Target Audience Rust developers frustrated by slow builds, teams managing large monorepos.
Core Feature Cargo wrapper that intercepts rustc invocations to measure specific generic instantiation costs and generate visual graphs.
Tech Stack Rust, Cargo API, time-series database (InfluxDB), Grafana dashboard.
Difficulty Low
Monetization Hobby: Open source tool.

Notes

  • Directly addresses the widespread discussion on compile times: embedding-shape: "I think traits makes the Rust build times grow really quickly", cardanome: "For release builds yes. For debug builds slow compile times kill productivity.", and esrauch: "It's never the case that only one thing is important.".
  • dwattttt explicitly asked for metrics: "I'm curious if this is tracked or observed somewhere; crater runs are a huge source of information, metrics about the compilation time of crates would be quite interesting."
  • Provides practical utility for a pain point that divides the community (runtime speed vs. developer velocity).

SafeThreadSkeptic

Summary

  • A linter/clippy-extension that flags codebases where thread safety guarantees are being bypassed unnecessarily (e.g., excessive unsafe or Arc<Mutex<>> wrappers on immutable data).
  • Suggests refactoring paths to leverage "fearless concurrency" by identifying data structures that can be safely shared or parallelized.
  • Includes a simulation mode to estimate potential performance gains from parallelization without actually running the code.

Details

Key Value
Target Audience Developers porting C++ code to Rust or optimizing legacy Rust codebases.
Core Feature AST analysis to detect concurrency anti-patterns and suggest standard library alternatives (e.g., Rayon integration).
Tech Stack Rust (syn, quote), Clippy plugin architecture.
Difficulty Medium
Monetization Revenue-ready: Enterprise consulting add-on (custom rule sets for specific industries).

Notes

  • Addresses the anecdote from bluGill: "Mozilla tried to parallelize Firefox’s style layout twice in C++, and both times the project failed." and the subsequent debate about Rust's safety enabling better concurrency.
  • treyd noted: "Code is typically run many more times than it's compiled, so this is a perfectly good tradeoff to make." This tool helps users make that tradeoff more effectively.
  • It targets the "social factor" mentioned by steveklabnik regarding how safety constraints impact developer behavior and eventual code performance.

RustBenchDiff

Summary

  • A service that takes a C code snippet and a Rust equivalent, compiles both with maximum optimizations (LTO, PGO), and generates a side-by-side diff of the generated assembly and performance metrics.
  • Focuses specifically on scenarios where aliasing rules (restrict in C vs. &mut in Rust) might differ, highlighting discrepancies in vectorization or loop unrolling.
  • Allows users to toggle compiler flags (like -fno-strict-aliasing) to see exactly when and how C performance catches up to Rust.

Details

Key Value
Target Audience Language enthusiasts, compiler engineers, and developers deciding between C and Rust for new projects.
Core Feature Automated compilation of dual codebases, assembly visualization, and micro-benchmarking of specific hot paths.
Tech Stack Godbolt Compiler Explorer API, Docker, JavaScript (for UI).
Difficulty High
Monetization Revenue-ready: Freemium model (limited requests per day) with paid tiers for extensive benchmarking.

Notes

  • Solves the core frustration of the discussion: gignico: "Does anyone know of an example of it happening in real code?" and Karliss: "Not exactly real world, but real code example..."
  • HN users love tools like Godbolt (Karliss linked one). This product abstracts the manual work of setting up the comparison for the specific aliasing argument.
  • It directly tests the hypothesis mentioned by aw1621107: "the rules for interpreting that text changed, and it's that difference in interpretation that permits better optimizations."

C2RustPerfMapper

Summary

  • An evolution of the c2rust transpiler that focuses specifically on performance implications of the translation.
  • It analyzes the resulting Rust code to identify where C idioms (like raw pointer arithmetic) remain, and suggests idiomatic Rust refactorings that might unlock compiler optimizations (aliasing info, lifetime analysis).
  • Generates a report detailing "Performance Debt" inherited from the C source and potential gains from Rust-specific features.

Details

Key Value
Target Audience Teams migrating legacy C systems to Rust, Security researchers.
Core Feature AST transformation analysis + heuristics to recommend refactoring specific constructs (arrays to Vectors, pointers to slices) for performance.
Tech Stack Python/Rust (for the transpiler logic), LLVM.
Difficulty High
Monetization Revenue-ready: Licensing for enterprise migration projects.

Notes

  • Addresses the comment by jandrewrogers: "I can write C that is as fast as C++. This requires many times more code that takes longer to write and longer to debug."
  • It offers a middle ground for the "social factors" debate: it quantifies the "effort" required to bridge the performance gap between the two languages during a rewrite.
  • HN commenters appreciate tools that automate rote tasks (steveklabnik's article discusses the difficulty of manual comparisons), making this a highly practical utility for real-world engineering challenges.

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