Matt Godbolt's blog
15 hours ago
- Compilers optimize loops by duplicating them for different conditions, known as 'loop unswitching'.
- At lower optimization levels (e.g., -O2), compilers may use conditional instructions like multiply-and-add to avoid branches inside loops.
- Loop unswitching moves invariant checks outside loops and creates specialized loop copies, trading code size for performance.
- Higher optimization levels enable loop unswitching, eliminating unnecessary operations (e.g., multiplication) when conditions remain constant.
- Trust compiler optimization decisions but understand trade-offs, verified via tools like Compiler Explorer.