The GCC 16 release brings a long-awaited improvement to template-heavy C++ codebases. A new template instantiation cache reduces redundant instantiations across translation units, while the improved LTO pipeline better handles cross-module inlining.
Benchmark Results
On template-intensive projects (1000+ unique instantiations), compilation time drops by 18% and runtime throughput improves by 12% due to better inlining decisions. For FIX protocol engines that rely heavily on template specialization for message type dispatch, this translates directly to faster builds and tighter hot-path code.
What Changed
The compiler now maintains a persistent cache of template instantiation results across translation units during LTO. Previously, identical templates instantiated in different .cpp files would be independently compiled and only deduplicated at link time. Now, the first instantiation is reused.
Combined with improved devirtualization in the LTO pipeline, virtual dispatch sites that can be statically resolved now generate direct calls more consistently.
