Branch Prediction and Speculation

Purpose

Explain how modern CPUs predict branches, execute speculatively, recover on mispredict, and why speculation created side channels (Spectre/Meltdown) — linking performance tuning with security-aware low-level coding.

When to Use

• Hot loop branchy code underperforms expectations
• Evaluating likely/unlikely or branchless refactors
• Understanding kernel retpoline, IBRS, and similar mitigations
• Secure coding around secret-dependent branches

Workflow

1. Branch predictor basics