LLVM-MOS
Ranked 15 of 18 c compilers by recommenders
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.
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.
10 people gave an opinion
- recommend it
- 7
- criticize it
- 3
- approval share
- 70%
Recommended in 2 of 13 months
- November 2025: recommended
- December 2025: recommended
- January 2026: not recommended
- February 2026: not recommended
- March 2026: not recommended
- April 2026: not recommended
- May 2026: not recommended
- June 2026: not recommended
- July 2026: not recommended
- August 2026: not recommended
- September 2026: not recommended
- October 2026: not recommended
- November 2026: not recommended (month in progress)
Why it doesn’t carry the badge
- 7 people recommend itNeeds 10 or more, not met.
- 2.3 recommenders for every criticNeeds 2 to 1 or better, met.
- Recommended in 2 of 13 monthsNeeds 4 or more, not met.
The same three rules apply to every product, and the badge can’t be bought. How the badge works
What people say about it
The reasons people give, with the number of comments that give each one. Open a reason to read what they said.
Why people recommend it
Each mark is one comment
Writes normal C with good code
“seems to generate good enough code - more than competitive with other high-level languages for the 6502”
Comment from 19 Nov 2025 in “Programming the Commodore 64 with .NET” “I could write pretty much normal C and have it work on the 6502”
Comment from 30 Nov 2025 in “LLVM-MOS – Clang LLVM fork targeting the 6502” Steady progress and worthwhile approach
“It's been amazing to see the progress on this project over the last 5 years.”
Comment from 30 Nov 2025 in “LLVM-MOS – Clang LLVM fork targeting the 6502” “so the LLVM-MOS approach is still very much worthwhile”
Comment from 30 Nov 2025 in “LLVM-MOS – Clang LLVM fork targeting the 6502”
What people warn about
Each mark is one comment
Weak register allocation and performance
“LLVM-MOS's register allocator is far from optimal for the 6502 architecture.”
Comment from 1 Dec 2025 in “LLVM-MOS – Clang LLVM fork targeting the 6502” “pretty soundly beaten in performance of generated code by Oscar64”
Comment from 30 Nov 2025 in “LLVM-MOS – Clang LLVM fork targeting the 6502”
Other c compilers people recommend
The four most recommended other c compilers, with the same counts for each, so you can compare like for like. The tick on each bar marks the 2 to 1 line the badge needs.
| Product | Recommend | Criticize | Approval | Months | Owned | Badge |
|---|---|---|---|---|---|---|
| Fil-C | 160 | 60 | 73% | 13 | — | Approved |
| Claude's C Compiler | 39 | 83 | 32% | 5 | — | — |
| Visual C++ | 29 | 17 | 63% | 12 | — | — |
| Tiny C Compiler (TCC) | 22 | 3 | 88% | 9 | — | Approved |
| LLVM-MOSThis page | 7 | 3 | 70% | 2 | — | — |
What people said
11 of the 12 comments that mention it, newest first. Each links to the original comment.
“this is a nice abstraction of what the assembly language programmer would have done themself.”
“LLVM-MOS's register allocator is far from optimal for the 6502 architecture.”
“these guys are the only ones I know that have ever been successful to any degree”
“there are too many compromises to make it suitable for writing a game”
“one of the best available 6502 assembly development environments, if you like Unix-style cross-assemblers”
“Some of the custom optimization passes introduced by this MOS backend are also of broader interest for the project”
“so the LLVM-MOS approach is still very much worthwhile”
“pretty soundly beaten in performance of generated code by Oscar64”
“It's been amazing to see the progress on this project over the last 5 years.”
“I could write pretty much normal C and have it work on the 6502”
“seems to generate good enough code - more than competitive with other high-level languages for the 6502”
Counts come from 1,795,640 Hacker News comments, November 2025 to November 2026. How we count. Report a mistake.