Xo 0.22 release notes

Introduction

Xo 0.22 builds Windows programs with Xo’s own backend and no C toolchain, cuts the size of LLVM builds to between a half and a third, speeds up the edit loop, makes HTTP and TLS cheaper, and fixes a heap overrun every native program had at startup since 0.21’s development.

Fixes

• The runtime’s root context registry used a byte offset as a slot index and wrote about 2 KB past a 296-byte runtime record at startup on every OS. It was silent on macOS and Linux and a crash at startup on Windows.

Ports

• Windows: Xo’s own x86-64 backend builds windows/amd64 (--backend=amd64) with its own COFF writer and PE linker, a checked-in import table, manifest and version resources, and no C runtime: no clang, lld-link, or Windows SDK (decision 0254). The default backend on x86-64 hosts stays LLVM for now (decision 0270).

Compiler

• Smaller binaries: xo’s code went from 40.18 MB to 31.78 MB built natively and from 89.82 MB to 32.59 MB built with LLVM; the Windows xo.exe from 160 MB to 63.65 MB.
• A faster edit loop: packed and lazily decoded cache entries, parallel borrow inference, and a front end cache for function bodies (decision 0220). Rebuilding xo after a one-constant edit went from about 9.5 s to about 6 to 8 s.

Runtime and standard library

• TLS is 8.2% and HTTP/2 9.2% cheaper per request on arm64, with cheaper JSON encoding and HTTP/1 headers.
• Faster allocation while other threads run.
• Task stacks are kept at their peak size: 97% fewer page faults in connection bursts.