When have we a micro-instruction in the ibuffer?

I am curious about what kind of instruction have  micro-instruction. And the commit below fix what kind of bugs.

```
https://github.com/vortexgpgpu/vortex/commit/54bb7009cd0ac08dc8ccc3e6bae098d145b54917#diff-ddb6ff9650c442ed464027e265dcf3d7424c3f84ef1bf93852c6665e3e527ccf 
```