Defaulted constructors may hurt performance in GCC: what to measure

What happened and what to do

Daniel Lemire's post questions whether C++ constructors should be defined as = default, arguing that this choice can have notable negative performance effects in recent GCC versions. According to the text, choosing between = default and explicit constructor bodies can affect compile time or the generated code, depending on the compiler version. The author points to his own papers for more detail.

In practice, a company that maintains C++ libraries or systems sensitive to performance should not assume the effect in either direction without measuring it. A concrete response is a reproducible benchmark pipeline: build critical modules with the GCC versions in use, compare compile time, binary size and execution time of sensitive functions, and record the results in a dashboard over time. The pipeline can run in CI on every compiler or code change, flagging regressions before they reach production. It is also worth adding a review rule that documents when to use = default and when an explicit body is justified, based on the measured numbers.

How the consultancy can help

Diagnosis of how GCC versions and constructor patterns affect compile time and performance of your C++ modules. We then implement a reproducible benchmark pipeline in CI, with a regression dashboard and review guidelines, running on your infrastructure with ongoing operation.

Next step

Send a short description of your C++ code, the compiler versions in use and what is sensitive to performance. We reply with a scoped proposal for diagnosis and implementation.