Improve cluster construction performance

[skyline75489]

Summary of the Pull Request

A tiny performance fix in renderer.cpp.

References

PR Checklist

• Closes #xxx
• CLA signed. If not, go over here 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

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:

Validation Steps Performed

Manually validated.

[skyline75489]

The ultimate solution may be something like #3458 . But that PR isn't going to land any time soon. AFAIK there's lots of things need to be done before landing something close to #3458.

[zadjii-msft]

This looks fine to me but I'd want to make sure that @miniksa signs off on this. Thanks!

[zadjii-msft]

@msftbot make sure that @miniksa signs off on this

[ghost]

Hello @zadjii-msft!

Because you've given me some instructions on how to help merge this pull request, I'll be modifying my merge approach. Here's how I understand your requirements for merging this pull request:

• I'll only merge this pull request if it's approved by @miniksa

If this doesn't seem right to you, you can tell me to cancel these instructions and use the auto-merge policy that has been configured for this repository. Try telling me "forget everything I just told you".

[miniksa]

Approved with the comment I merged in here to remind us what the variable is for.

[ghost]

🎉Windows Terminal Release Candidate v0.11.1251.0 (1.0rc1) has been released which incorporates this pull request.:tada:

Handy links:

• Release Notes
• Store Download

[DHowett]

🎉 Once again, thanks for the contribution!

This pull request was included in a set of conhost changes that was just
released with Windows Insider Build 20161.