apple-performance-memory

name	apple-performance-memory
description	Diagnose Apple app launch/runtime performance, SwiftUI invalidation, hangs, Instruments traces, Top Functions, ETTrace profiles, dSYMs, memgraphs, leaks, retain cycles, and Foundation Models traces. Use when an Apple app is slow, janky, memory-heavy, leaking, hanging, or needs before/after profiling evidence.

Apple Performance / Memory

Purpose

Use this skill when the question is runtime cost, not merely build correctness. Start with code and scenario clarity, then pick the smallest trace that answers the question.

Workflow

1. Define the scenario.

   • launch, first screen, scroll, navigation, search, import/export, HealthKit sync, model generation, background work, watch handoff, or memory growth
   • same scheme, destination, configuration, data, and steps for before/after comparisons

2. Inspect code first.

   • SwiftUI body churn, expensive computed properties, broad Observation invalidation, unstable IDs, nested lists, image decoding, synchronous work on the main actor
   • retain cycles, long-lived tasks, unbounded caches, NotificationCenter/KVO/timer ownership, task cancellation, and actor isolation problems

3. Pick the proof.

   • Instruments or xctrace for CPU, hangs, allocation, leaks, and launch
   • Top Functions for hot-stack narrowing
   • ETTrace helpers for iOS Simulator latency and stack comparison
   • dSYM collection when traces need symbolication
   • memgraph helpers for retained objects and leaks
   • Foundation Models Instrument for prompt, response, token, and tool-call behavior
   • XcodeBuildMCP coverage/log workflows when the issue is tied to tests or runtime logs

4. Run the narrow command.

   • Keep raw trace files out of git unless the repo explicitly stores performance artifacts.
   • Store temporary evidence under /private/tmp or another ignored location.
   • Preserve the exact command, destination, device, OS, build configuration, and app version.

5. Fix and compare.

   • Make one causal change at a time where possible.
   • Re-run the same scenario.
   • Report before/after evidence and residual risk.

Bundled Helpers

• scripts/analyze_flamegraph_json.py
• scripts/collect_ios_dsyms.sh
• scripts/capture_sim_memgraph.sh
• scripts/summarize_memgraph_leaks.py

References

• references/swiftui/