--- title: Fil-C: Garbage In, Memory Safety Out! - Filip Pizlo |... description: Fil-C is a memory-safe compiler for C and C++ built as a fork of Clang/LLVM. It instruments LLVM IR with 'invisible capabilities' — hidden bounds metadata that... canonical: https://daily.dev/posts/fil-c-garbage-in-memory-safety-out---filip-pizlo-ssw-2026-ceg9uvygn twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Fil-C: Garbage In, Memory Safety Out! - Filip Pizlo | SSW 2026 | daily.dev og:description: Fil-C is a memory-safe compiler for C and C++ built as a fork of Clang/LLVM. It instruments LLVM IR with 'invisible capabilities' — hidden bounds metadata that... og:url: https://daily.dev/posts/fil-c-garbage-in-memory-safety-out---filip-pizlo-ssw-2026-ceg9uvygn og:image: https://api.daily.dev/og/posts/ceg9uVYgn.png og:image:alt: Fil-C: Garbage In, Memory Safety Out! - Filip Pizlo | SSW 2026 og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Fil-C: Garbage In, Memory Safety Out! - Filip Pizlo | SSW 2026 **[Lobsters](https://daily.dev/sources/lobsters)** · 51 min read · 0 upvotes · 0 comments ## Summary Fil-C is a memory-safe compiler for C and C++ built as a fork of Clang/LLVM. It instruments LLVM IR with 'invisible capabilities' — hidden bounds metadata that travels with every pointer but cannot be tampered with by user code. This prevents out-of-bounds accesses, use-after-free, and type confusion without requiring code rewrites in most cases. The runtime uses an accurate, concurrent, non-moving garbage collector to handle use-after-free deterministically. Performance ranges from slightly faster than Rust (for SIMD-heavy code like Blake3) to about 4-6x slower in typical workloads. The project runs ~94 million lines of C/C++ code including LibreOffice, GTK, CPython, OpenSSH, and a full Linux userland compiled with Fil-C. It supports C23, C++23, threads, atomics, inline assembly (with safety checks), setjmp/longjmp, shared memory, and syscall filtering. Binary compatibility with non-Fil-C libraries is a non-goal. The project is a personal side project currently limited to Linux x86-64. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Similar posts on daily.dev - [Fil-C](https://daily.dev/posts/fil-c-lpbkzhfzw) · Lobsters · 4 upvotes · 1 comments - [A simplified model of Fil-C](https://daily.dev/posts/a-simplified-model-of-fil-c-dg6tupxkq) · Hacker News · 0 upvotes · 0 comments --- Tags: [#general-programming](https://daily.dev/tags/general-programming), [#c](https://daily.dev/tags/c), [#c++](https://daily.dev/tags/c++) [View this post on daily.dev](https://daily.dev/posts/fil-c-garbage-in-memory-safety-out---filip-pizlo-ssw-2026-ceg9uvygn) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"Fil-C: Garbage In, Memory Safety Out! - Filip Pizlo | SSW 2026","url":"https://daily.dev/posts/fil-c-garbage-in-memory-safety-out---filip-pizlo-ssw-2026-ceg9uvygn","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/fil-c-garbage-in-memory-safety-out---filip-pizlo-ssw-2026-ceg9uvygn"},"datePublished":"2026-07-24T11:37:57.136Z","dateModified":"2026-07-24T22:10:49.472Z","description":"Fil-C is a memory-safe compiler for C and C++ built as a fork of Clang/LLVM. It instruments LLVM IR with 'invisible capabilities' — hidden bounds metadata that...","image":"https://i.ytimg.com/vi/5F-2Y1LPRek/sddefault.jpg","thumbnailUrl":"https://i.ytimg.com/vi/5F-2Y1LPRek/sddefault.jpg","isAccessibleForFree":true,"articleSection":"Lobsters","inLanguage":"en","publisher":{"@type":"Organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180}},"author":{"@type":"Organization","name":"Lobsters","logo":"https://media.daily.dev/image/upload/s--tl8v_Fku--/f_auto,t_logo/v1698841318/logos/lobste.jpg","url":"https://daily.dev/sources/lobsters"},"commentCount":0,"discussionUrl":"https://daily.dev/posts/fil-c-garbage-in-memory-safety-out---filip-pizlo-ssw-2026-ceg9uvygn","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":0},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":"general-programming,c,c++","timeRequired":"PT51M","video":{"@type":"VideoObject","name":"Fil-C: Garbage In, Memory Safety Out! - Filip Pizlo | SSW 2026","description":"Fil-C is a memory-safe compiler for C and C++ built as a fork of Clang/LLVM. It instruments LLVM IR with 'invisible capabilities' — hidden bounds metadata that...","thumbnailUrl":"https://i.ytimg.com/vi/5F-2Y1LPRek/sddefault.jpg","uploadDate":"2026-07-24T11:37:57.136Z","duration":"PT51M","url":"https://api.daily.dev/r/ceg9uVYgn","embedUrl":"https://www.youtube.com/embed/5F-2Y1LPRek"}} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"Lobsters","item":"https://daily.dev/sources/lobsters"},{"@type":"ListItem","position":3,"name":"Fil-C: Garbage In, Memory Safety Out! - Filip Pizlo | SSW 2026"}]} ```