Summary - Compiler internals
- Rust course
- Expert
- Lesson 6/46
- 5 min
Combine HIR, MIR and LLVM IR to draw a compilation pipeline.
Compiler internals summary
The compilation pipeline: tokens → AST (macros, name resolution) → HIR (sugar removed, type checking, trait resolution) → MIR (control-flow graph, borrow checking, NLL, constant evaluation) → LLVM IR (optimization) → machine code. Type inference works by constraint unification within a function. Debug and release builds apply different checks and optimizations; for example, integer overflow checking is on by default only in debug.
Overflow with explicit intent
Integer methods make what happens on overflow the same in every build:
let x: u8 = 255;
println!("{:?}", x.checked_add(1)); // None
println!("{}", x.wrapping_add(1)); // 0
println!("{}", x.saturating_add(1)); // 255
println!("{:?}", x.overflowing_add(1)); // (0, true)wrapping_* is the natural choice for counters and hashes, saturating_* for bounded values, checked_* for validation.
Practice Overflow methods
For let x: u8 = 255;, print the results of checked_add(1) ({:?}), wrapping_add(1) and saturating_add(1) on one line separated by spaces.
Starter code
fn main() {
// buraya yaz
}Sample solution
fn main() {
let x: u8 = 255;
println!("{:?} {} {}", x.checked_add(1), x.wrapping_add(1), x.saturating_add(1));
}Expected output
None 0 255
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What happens to <code>255u8 + 1</code> in a release build (with default settings)?
- Always panics
- It becomes 256
- Always a compile error
- It wraps to 0; in debug it panics Correct answer
Explanation: To keep behaviour independent of the build, state the intent explicitly: checked_add, wrapping_add, saturating_add. (The compiler already catches a constant expression as an error.)
2 Stay at the limit
let x: u8 = 255;
let y = x.____(1); // 255let x: u8 = 255;
let y = x.saturating_add(1); // 255Explanation: saturating_add stays at the type's limit on overflow.
3 Method and 255u8 + 1 result
| Term | Meaning |
|---|---|
checked_add |
None |
wrapping_add |
0 |
saturating_add |
255 |
overflowing_add |
(0, true) |