The Superficial Syntax

At the surface, if chains and switch statements are just two ways of writing conditional control flow:

// if-else chain
if (x == 0) { foo(); }
else if (x == 1) { bar(); }
else if (x == 2) { baz(); }
else { qux(); }

// switch
switch (x) {
    case 0: foo(); break;
    case 1: bar(); break;
    case 2: baz(); break;
    default: qux();
}

They read almost identically. If you’re coding business logic, pick whichever looks clean. But once you care about cycles per decision, the similarities end.

What the Compiler Actually Emits

Modern compilers don’t implement these literally. Under the hood, the choice of if vs. switch often controls how the compiler lowers the logic into machine instructions.

If-else chain: usually compiled into a sequence of conditional branches:

cmp x, 0
je  Lfoo
cmp x, 1
je  Lbar
cmp x, 2
je  Lbaz
jmp Lqux

Switch: depending on the density of case values, compilers can pick different strategies:

1. Jump table (O(1) dispatch):

cmp x, 2
ja  Lqux
jmp [jump_table + x*8]

2. Binary search tree of branches (O(log n) dispatch).

3. Straight-line compares (like an if-else).

In other words: with switch, you hint to the compiler that this is a dispatch on a discrete set of integer values, and it may optimize it aggressively.

3. Branch Prediction: The Real Bottleneck

Modern CPUs can predict branches very well… until they can’t.

If-else chain: Each if is a branch the predictor must learn. If x is distributed uniformly over many cases, predictors get confused, and you see frequent mispredictions. Each misprediction costs ~15 cycles, which is catastrophic in a low-latency path.

Switch with jump table: Avoids unpredictable branching. Instead of taking multiple conditional jumps, the CPU computes a table index and jumps directly. No branch prediction needed—control flow becomes data-dependent, not history-dependent. This is often the fastest path if cases are dense.

4. Cache & iTLB Effects

There’s a subtle tradeoff here:

Jump tables can blow up your instruction footprint. If you have 50 cases, you’re scattering execution across 50 basic blocks, which might not all fit neatly into I-cache.

If chains are compact, meaning that linear code streams nicely in cache. If hot values are clustered at the top of the chain (and branch predictor learns that), you can win on cache locality even if the asymptotic dispatch cost looks worse.

TL;DR Recommendation:

• If you know the hot cases: Use an if-else chain with the most frequent cases first. Branch predictor loves this → fewer mispredictions → faster execution.

• If cases are dense and roughly uniform: Use a switch—compiler can emit a jump table → O(1) dispatch.

And always remember to measure using microbenchmarks as CPU behavior is subtle.