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branch-prediction-and-speculation

Use when explaining branch predictors, mispredict penalties, speculative execution, Spectre or Meltdown mitigations, or branchless code. Not for pipeline stage theory: use cpu-pipelines-and-hazards.

.devin/skills/branch-prediction-and-speculation/SKILL.md

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Last checked
Nov 4, 2026

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55
Repository last updated
Sep 28, 2026
License
Apache-2.0

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# Branch prediction and speculation

## Contract

| Field | Bound contract |
|---|---|
| Trigger | Branchy hot code underperforms, a `likely` or branchless refactor needs judgment, a kernel mitigation such as retpoline or KPTI needs explaining, or code branches on secret data. |
| Authority | Read-only. The skill runs `perf stat` on a user-named binary, reads sysfs, and answers in chat. Nothing on disk changes, so there is nothing to roll back. No remote mutation. |
| Side effect | Chat output only. `perf stat` writes counters to stdout. |
| Done | The answer names the branch that mispredicts or the speculation path that leaks, gives a measured `branch-misses` count where a binary exists, and states the fix with the condition under which it helps. |

## Inputs

- Code or hot loop (required): the source or disassembly around the branch in question.