build-performance

Comprehensive build performance optimization with Build Timeline analysis, type checking improvements, parallelization workflows, and Xcode 26 compilation caching.

When to Use

• Build times are slow
• Investigating build performance
• Analyzing Build Timeline (Xcode 14+)
• Identifying type checking bottlenecks
• Optimizing incremental builds
• CI/CD build time optimization
• Enabling Xcode 26 compilation caching
• Reducing module variants in explicitly built modules

Example Prompts

• "My builds are slow, how can I speed them up?"
• "How do I analyze the Build Timeline?"
• "What is compilation caching in Xcode 26?"
• "Why is the same module being built multiple times?"
• "How do I enable parallel script execution?"

What This Skill Provides

Build Timeline Analysis

• Critical Path Optimization — Identify and shorten the longest chain of dependent tasks
• Timeline Visualization — Interpret empty vertical space (idle cores), long horizontal bars (slow tasks)
• Parallelization Gaps — Detect targets waiting unnecessarily

10 Optimization Patterns

Pattern	What It Does	Impact
1. Type Checking	Identify slow functions with -warn-long-function-bodies	10-30%
2. Build Phase Scripts	Conditional execution, sandboxing, parallel scripts	5-10s saved
3. Compilation Mode	Incremental (Debug) vs Whole Module (Release)	40-60%
4. Build Active Architecture	Only build for current device in Debug	40-50%
5. Debug Information	DWARF (Debug) vs DWARF with dSYM (Release)	3-5s saved
6. Target Parallelization	Enable parallel builds in scheme	~2x faster
7. Emit Module	Xcode 14+ automatic optimization	20-40%
8. Eager Linking	Xcode 14+ automatic optimization	—
9. Compilation Caching	Xcode 26 cache across clean builds	20-40%
10. Explicitly Built Modules	Three-phase build, reduce module variants	10-30%

Xcode 26 Features

Compilation Caching — Reuse compiled artifacts across clean builds:

Build Settings → COMPILATION_CACHE_ENABLE_CACHING → YES

Explicitly Built Modules — Default for Swift in Xcode 26. Separates build into Scan → Build Modules → Compile phases. Use "modules report" filter in build log to identify duplicate module variants.

Quick Win

Use the /axiom:optimize-build command to automatically scan for common issues:

/axiom:optimize-build

The build-optimizer agent scans build settings, scripts, and compiler flags, providing specific fixes with expected time savings.

Workflow

1. Measure Baseline — Clean build + incremental build times
2. Analyze Build Timeline — Product → Perform Action → Build with Timing Summary
3. Identify Bottlenecks — Compilation? Linking? Scripts? Module variants?
4. Apply ONE optimization — Don't batch changes
5. Measure Improvement — Compare against baseline
6. Verify in Build Timeline — Visual confirmation

Related

• build-debugging — Fixing broken builds (dependency conflicts, SPM issues)
• xcode-debugging — Environment-first Xcode diagnostics (zombie processes, simulator)
• /axiom:optimize-build — Automated scanning agent for quick wins

Resources

WWDC: 2018-408, 2022-110364, 2024-10171, 2025-247

Docs: /xcode/improving-the-speed-of-incremental-builds, /xcode/building-your-project-with-explicit-module-dependencies

Tools: Build Timeline (Xcode 14+), Modules Report (Xcode 16+), Build with Timing Summary