strength reduction

A compiler trick that swaps a slow operation for cheaper ones that give the same answer, like a shift instead of a multiply by 8.

Strength reduction replaces an expensive operation with an equivalent cheaper sequence, such as x * 8 with x << 3, x * 5 with lea [x + x*4], or division by a constant with multiplication.

Examples

Compilers turn x * 8 into x << 3, and x * 5 into lea eax, [rdi + rdi*4].