Performance implications of unchecked functions like unwrap_unchecked, unreachable, etc.

Hi everyone,

I'm working on a high-performance rust project, over the past few months of development, I've encountered some interesting parts of Rust that made me curious about performance trade-offs.

For example, functions like unwrap_unchecked and core::hint::unreachable. I understand that unwrap_unchecked skips the check for None or Err, and unreachable tells the compiler that a certain branch should never be hit. But this raised a few questions:

• When using the regular unwrap, even though it's fast, does the extra check for Some/Ok add up in performance-critical paths?
• Do the unchecked versions like unwrap_unchecked or unreachable_unchecked provide any real measurable performance gain in tight loops or hot code paths?
• Are there specific cases where switching to these "unsafe"/unchecked variants is truly worth it?
• How aggressive is LLVM (and rust's optimizer) in eliminating redundant checks when it's statically obvious that a value is Some, for example?

I’m not asking about safety trade-offs, I’m well aware these should only be used when absolutely certain. I’m more curious about the actual runtime impact and whether using them is generally a micro-optimization or can lead to substantial benefits under the right conditions.

Thanks in advance.