I made a build visualizer to understand Bun's compile times
- ID
- 24022
- Status
- summarized
- Published
- 12 Sep 2026, 10:45 PM
- Fetched
- 14 Sep 2026, 3:32 AM
- Provider
- Hacker News
- Category
- dev-community
- Original URL
- https://lalitm.com/post/buildprof/
- Source URL
- https://hnrss.org/best
Summary
- Score
- 7.0
- Created
- 14 Sep 2026, 3:34 AM
- Tags
- Audience
- developersvibe_coders
What happened
Lalit Maganti built buildprof, an open-source Linux build tracing tool that records every process and subprocess in a build command and visualizes them on a single timeline. They used it to investigate Jarred Sumner's claim that Bun's Rust build was 5× faster than its old Zig build, reproducing the numbers (24m24s Zig vs 5m40s Rust on a 6-core VM) and identifying that the Zig build used Full LTO while the Rust build used ThinLTO—a difference that preserves parallelism and can dramatically affect build time.
Why it matters
If your project uses Full LTO, switching to ThinLTO could cut build times significantly without changing languages—this is a concrete, low-cost lever to test. The buildprof tool itself is immediately usable: prefix any build command with 'buildprof --' to see a timeline of where compile time actually goes, exposing poor parallelism, repeated work, or slow dependency downloads.
Discussion angle
How much of the 'Rust is faster to compile than Zig' narrative is actually just LTO strategy, and should teams default to ThinLTO for CI builds while reserving Full LTO for release?