# LLVM-MOS

7 Hacker News commenters recommended LLVM-MOS and 3 criticized it, November 2025 to November 2026. It was recommended in 2 of 13 months.

**Verdict:** Clang-based C compiler for the 6502 that lets people write normal C and produces good enough code. Critics say it trails Oscar64 in speed and its register allocator is weak.

## Why people recommend it

- Writes normal C with good code (2 comments): "seems to generate good enough code - more than competitive with other high-level languages for the 6502" ([source](https://news.ycombinator.com/item?id=45983771)) "I could write pretty much normal C and have it work on the 6502" ([source](https://news.ycombinator.com/item?id=46098813))
- Steady progress and worthwhile approach (2 comments): "It's been amazing to see the progress on this project over the last 5 years." ([source](https://news.ycombinator.com/item?id=46099110)) "so the LLVM-MOS approach is still very much worthwhile" ([source](https://news.ycombinator.com/item?id=46100878))

## What people warn about

- Weak register allocation and performance (2 comments): "LLVM-MOS's register allocator is far from optimal for the 6502 architecture." ([source](https://news.ycombinator.com/item?id=46113093)) "pretty soundly beaten in performance of generated code by Oscar64" ([source](https://news.ycombinator.com/item?id=46100116))

## Alternatives hackers recommend

- [Fil-C](https://hackerapproved.com/p/fil-c.md): 160 recommend
- [Claude's C Compiler](https://hackerapproved.com/p/claude-s-c-compiler.md): 39 recommend
- [Visual C++](https://hackerapproved.com/p/visual-c-plus-plus.md): 29 recommend
- [Tiny C Compiler (TCC)](https://hackerapproved.com/p/tcc.md): 22 recommend
- [Microsoft Visual C++ compiler (MSVC)](https://hackerapproved.com/p/msvc.md): 20 recommend

## Cite as

Hacker Approved, "LLVM-MOS", https://hackerapproved.com/p/llvm-mos/ (counts from 1,795,640 Hacker News comments, November 2025 to November 2026).