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RuneStone-TechRuneStone-Tech/optimize-anything/skills/backend/c++/SKILL.md

cpp-optimizer

Skill1 starsChanged 8 days agoMITView on GitHub

Audit and optimize C++23 codebases (GCC 16, Clang 22, MSVC 14.52, CMake) for build flags/LTO/PGO, RAII and smart-pointer ownership, copies/moves and allocations, cache locality and data layout, threading/atomics/coroutines, I/O and formatting, UB/sanitizers/hardening, and profiling, with real before/after measurement. Always produces a written findings report and a fix plan for approval before touching code. Use this whenever the user mentions slow C++, memory growth, `shared_ptr` cycles, copies in hot loops, CMake flags, LTO/PGO, ASan/TSan, C++23/C++26, or "optimize my C++ code" -- even if they never say audit or optimize.

The file

We split this skill into the rules it gives an agent

3 rules. About 0 are common, 0 are distinctive, and 3 are very specific to this project.

  • ≈0

    Common · estimate

    Many files like this have a rule of this kind.

  • ≈0

    Distinctive · estimate

    This author's own choices. Worth a look.

  • 3

    Very specific

    Tied to their project's names, files or tools. Probably skip.

  • Common
  • Distinctive
  • Very specific
  1. Very specific:

    Run python <skill-dir>/scripts/audit.py <project-root> -- static scan of build files and sources for legacy standards, debug flags, raw …

    line 15
  2. Very specific:

    Read references/tooling.md once: what can be measured here.

    line 17
  3. Very specific:

    Use plan mode: EnterPlanMode (load with ToolSearch if deferred), write the plan, present with ExitPlanMode.

    line 39

≈ “Common” is an estimate: at least 1 in 5 of the 350,495 skill files we read have a rule of the same kind, not the same words. “Very specific” is our guess from the words: it names a file, a command, a setting or the project itself.

Keep what fits and drop the rest. Your version, ready for your agents.
Files
SKILL.md

C++ Optimizer

C++ performance is ownership, data layout and build flags. The published standard is C++23 (ISO/IEC 14882:2024); C++26 was finalized by WG21 in March 2026 but failed its ISO DIS ballot in October 2026, so treat -std=c++26 as experimental. Optimize release builds, remove copies/allocations, and make concurrency explicit.

Workflow

1. Scope (quick)

  • Find the project root and record the toolchain: C++ standard/compiler, CMake presets, build type/flags, standard library, sanitizer/hardening setup, threading/coroutines, and target ABI.
  • Run python <skill-dir>/scripts/audit.py <project-root> -- static scan of build files and sources for legacy standards, debug flags, raw ownership, copies/allocations, shared_ptr cycles, data races, iostream/format cost, missing sanitizers, with file:line evidence. Use --json to post-process.
  • Classify the pain: throughput/latency, memory growth, CPU saturation, concurrency/correctness, I/O or database cost, build/startup, or safety/maintenance. Ask which hurts if unclear.
  • Read references/tooling.md once: what can be measured here.

2. Audit

The script finds cheap leads; you find the rest by reading the hot path and the build. Read the build manifest, entrypoint, the 3-5 hot functions/endpoints and the data layer. Load only what applies:

| Build, toolchain and runtime | references/build-runtime.md | | Memory, ownership and concurrency | references/memory-concurrency.md | | I/O, formatting and data | references/io-data.md | | Safety and quality | references/safety-quality.md | | Measurement | references/tooling.md |

Measure, never guess. Build with production settings, run with production data/load, and profile that. Debug builds, dev servers and a single request are not evidence. Take a profile before micro-optimizing and a heap/allocator snapshot before raising limits.

Mark each finding Confirmed (profile/load/code evidence) or Suspected (needs measuring).

3. Report

Fill assets/report-template.md, save it as C++_OPTIMIZATION_REPORT.md in the project root, and show the user. Five-line summary, findings table by impact/effort, then per-finding detail (evidence, why it hurts, fix, risk, behavior impact). Group near-duplicates.

4. Plan -- then stop for approval

Use plan mode: EnterPlanMode (load with ToolSearch if deferred), write the plan, present with ExitPlanMode; if unavailable show it in chat and wait for an explicit "go". Structure:

  1. Quick wins -- build flags, missing indexes/caching, timeouts/pool limits, avoidable allocations/copies, sync I/O in hot paths, missing await/join, safer bounds checks, log noise, config limits. Low risk.
  2. Structural -- bound concurrency, batch N+1, stream large payloads, change data structures/ownership, split hot paths, cache correctly, connection/worker pools, graceful shutdown, observability. Name each behavior change.
  3. Heavy -- language/toolchain major upgrade, runtime/GC change, framework/ORM swap, architecture change, AOT/trimming, database migration. Separately approved. Each step: files touched, expected effect, how to verify, how to roll back.

5. Fix

Only approved items, in small groups. After each: build with production flags, run the test suite, and re-run the same benchmark/profile. A break must trace to one change. Do not mix a toolchain major upgrade with optimization edits. If a change alters ownership, concurrency, API/DB semantics or failure behavior, stop and ask.

6. Verify and wrap up

Re-measure the same workload and data: throughput and p50/p95/p99, CPU, RSS/heap, allocations/GC, I/O, error rate, build time and binary/image size. State plainly what could not be measured. End with deferred items and one suggested next step.

Principles

  • C++23 is the published target. C++26 is not an ISO-published standard yet; use it only experimentally.
  • RAII and value semantics first. Ownership and lifetime bugs are performance bugs.
  • Count copies and allocations. reserve, moves, string_view and span beat micro-tuning.
  • Concurrency is a design. Threads, atomics and coroutines need ownership and shutdown rules.
  • Measure with sanitizers and a profiler. A fast wrong answer is still wrong.

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