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## Summary of the Pull Request
A tiny performance fix in `renderer.cpp`.
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## References
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## PR Checklist
* [ ] Closes #xxx
* [X] CLA signed. If not, go over [here](https://cla.opensource.microsoft.com/microsoft/Terminal) and sign the CLA
* [ ] Tests added/passed
* [ ] Requires documentation to be updated
* [ ] I've discussed this with core contributors already. If not checked, I'm ready to accept this work might be rejected in favor of a different grand plan. Issue number where discussion took place: #xxx
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## Detailed Description of the Pull Request / Additional comments
The cluster construction code is intensively called during rendering. Even though a single `back()` is fast, but accumulated `back()`s still take a noticiable amount of CPU cycles.
Before:
After:
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## Validation Steps Performed
Manually validated.
97d6456476
