**System Information**
Operating system: Windows-10-10.0.18362-SP0 64 Bits
Graphics card: GeForce GTX 980 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 445.75
**Blender Version**
Broken: version: 2.83 (sub 15), branch: master, commit date: 2020-04-24 15:23, hash: `rBa8441fc90086`
Worked: Never (2.79+)
**Short description of error**
Adding a Mirror Modifier and using an empty or another object to mirror across, causes slow viewport performance.
**Exact steps for others to reproduce the error**
{F8497811}
# Open file
# Move Suzanne - Notice performance
# Remove Mirror Object from mirror modifier
# Move Suzanne - Performance much better
You can apply subdiv modifier, it shouldn't have an effect.