cargo-show-asm
A cargo subcommand to display assembly, LLVM-IR, MIR, and WASM generated for Rust code.
What is cargo-show-asm?
cargo-show-asm is a Cargo subcommand that displays the low-level code generated by the Rust compiler, including assembly, LLVM-IR, MIR, and WebAssembly. It helps developers understand how their Rust code translates to machine code, enabling performance optimization and debugging of compilation behavior. The tool addresses the need for visibility into compiler output without the overhead of manual inspection.
Rust developers working on performance-critical applications, compiler enthusiasts, and those needing to debug or optimize generated code. It's particularly useful for systems programmers, embedded developers, and anyone investigating compiler behavior or WebAssembly output.
Developers choose cargo-show-asm because it provides accurate, fast analysis without forcing recompilation, supports multiple output formats and architectures, and offers clean, customizable output. It's a maintained alternative to cargo-asm with better performance and more features.
Overview
cargo subcommand showing the assembly, LLVM-IR and MIR generated for Rust code
Use Cases
Best For
- Optimizing Rust code by inspecting generated assembly
- Debugging compiler behavior and understanding optimizations
- Analyzing WebAssembly output for Rust projects
- Learning how Rust code translates to low-level representations
- Comparing different compiler flags or target architectures
- Investigating inlining decisions and function call chains
Not Ideal For
- Windows-based development environments requiring robust cross-platform tool support
- Teams preferring graphical or IDE-integrated tools over command-line utilities for code analysis
- Projects where minimizing build time is critical and extra compilation or analysis steps are unwanted
- Developers focused solely on high-level application logic without need for assembly or compiler internals debugging
Pros & Cons
Pros
Respects the user's actual build settings and avoids unnecessary recompilation, ensuring output matches the real compilation process as stated in the philosophy section.
Supports assembly (Intel or AT&T syntax), LLVM-IR, MIR, WASM, and llvm-mca analysis, providing comprehensive insights into different compilation stages from the README features list.
Can display Rust source code alongside generated assembly with the '--rust' flag, making it easier to debug and understand the mapping between high-level and low-level code.
Allows analysis of specific functions, crates, binaries, examples, tests, or benchmarks with configurable context depth for call chains, as detailed in the usage examples.
Cons
The README explicitly states 'Limited support for Windows', which can hinder developers on that platform and may lead to compatibility issues or missing features.
With numerous options and flags for postprocessing, targeting, and output formats, the tool can be overwhelming for users not familiar with compiler internals or detailed CLI usage.
MIR output relies on rustc's human-readable format, which the README notes is not stable and may change between compiler versions, affecting reliability for long-term projects.
Frequently Asked Questions
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