LinkTime

Linktime is a term used in software build processes to describe the stage at which object code and libraries are linked to produce an executable or library. It is often used to refer to link-time optimization (LTO), a capability that performs cross-module optimizations during the linking phase rather than inside individual translation units.

How link-time optimization works: During compilation, a compiler can emit intermediate representations or other linkable artifacts for each translation unit. At link time, the linker uses these artifacts to perform whole-program optimization, allowing inlining across modules, cross-module constant propagation, dead code elimination, and better code layout. This can improve runtime performance and sometimes reduce binary size, but it can also increase build times and complicate incremental builds and debugging.

Benefits and trade-offs: LTO enables optimizations that are not possible when each translation unit is optimized in isolation, potentially yielding faster and smaller programs. However, it requires an LTO-capable toolchain and can impose higher memory and CPU requirements during builds. Compatibility issues may arise with certain languages, debuggers, or binary interfaces, and incremental development workflows may be less responsive during link-time analysis.

Common implementations: Many modern toolchains support link-time optimization. GCC and Clang offer LTO via the -flto flag, enabling cross-module optimizations with suitable linkers. Microsoft Visual C++ provides similar functionality through Whole Program Optimization and related options. Effective use of link-time optimization often depends on the entire build chain and the targeted platform or runtime.

See also: compilation, linker, whole-program optimization, optimization techniques.