Faster Debugging for Massive MSVC-Based Projects in CLion
CLion provides several bundled debuggers, including a modified version of the LLDB for the MSVC toolchain used on Windows. This custom JetBrains LLDB has a number of performance and accuracy improvements. Among other things, it supports an optimized mechanism for handling PDB files containing debugging data.
Recently, the debugger received another performance boost: the Step Over action now executes up to 50 times faster, and in some cases, the execution time has been reduced from seconds to tens of milliseconds. This speed increase is especially beneficial for massive C++ projects with hundreds of thousands of lines of code and gigabytes of debug symbols.
Rider and CLion use this custom LLDB-based debugger, so these improvements will benefit users of both IDEs. We encourage you to read the Rider team’s blog post for a deep dive into the optimizations that made this possible, but here is the short version.
What is behind the optimization
Here is what the team has done to improve the LLDB performance:
- Caching of addresses not found in debug symbols.
- Optimizations in expression evaluation that affect overall debugger performance, including stepping.
- Optimization of the stepping process when dealing with inlined functions.
- Expanding the LLDB SB API to help optimize thread plan performance.
The results
The improvements deliver up to 50x faster stepping times, with most operations now completing in less than 100ms. Here is a comparison of stepping performance on a large C++ project running in Rider 2024.3 and 2025.1 with the optimization enabled:
You can expect similar results in CLion, as it uses the same LLDB debugger for the MSVC toolchain.
For more information, check out the Rider team’s blog post.
Conclusion
These improvements are already available in the latest CLion EAP build. Feel free to download it, try the debugger, and share your feedback by submitting a ticket to our issue tracker or commenting below.
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