Communication Between the Compiler, the Build System, and Beyond

Modern POSIX-like systems lose significant optimization opportunities because compilers, build systems, and package managers do not share dependency and resource information. When C compilation units are compiled independently the compiler can only optimize within a single file; link-time optimization (LTO) partly addresses whole-program optimization but happens late and depends on compatible IR. Integrating the build system with the compiler enables whole-program optimization earlier, avoids redundant header parsing and AST rebuilding, and supports finer-grained incremental compilation (down to function level) by treating all sources that produce an output as one compilation unit. A simple example shows a caller passing a constant could be optimized away entirely if the compiler knew both caller and callee together; a build-aware compiler can also cache IR/AST between files and avoid writing intermediate IR to disk.

Extending integration to the package manager multiplies benefits: packages would carry explicit build and dependency descriptions so the build graph spans package boundaries, enabling cross-package whole-program optimization without needing distributed IR artifacts and allowing safe, atomic, incremental upgrades. A declarative system configuration can compute exact file-level dependencies, rebuild only affected code paths when options change, and install immutable system images. The same dependency-aware information can be fed further into system components such as the filesystem and scheduler to unlock additional optimizations, improved resource management, and more transparent system maintenance.