Comment by pjmlp

Here is a list, not easy to track all of them down, but maybe as keywords to easy googling.

- structs

- unsafe code

- stack allocation in unsafe code (think alloca())

- attribute annotations for packing and inline calls across assemblies

- ref parameters

- ref returns

- readonly ref parameters

- Span<> and Memory<>

- Native memory allocation via MarshalInterop, SafeHandles

- Buffer and ArraySegment

- SIMD (with RyuJIT)

- Profiled code cache for JIT code background generation between executions (System.Runtime.ProfileOptimization)