Tracing Compilation Events

Logs every compilation event with timing, tier levels, success/failure status, and invalidation reasons. Essential for understanding what the compiler is doing.

When to Use This Skill

• Verify hot code is compiling
• Diagnose compilation failures and bailouts
• Track recompilation cycles
• Understand tiered compilation behavior

Quick Start

# Basic compilation trace
<launcher> --experimental-options \
  --engine.TraceCompilation <program>

# With timing details
<launcher> --experimental-options \
  --engine.TraceCompilation \
  --engine.TraceCompilationDetails <program>

# Combined with performance warnings (RECOMMENDED)
<launcher> --experimental-options \
  --engine.TraceCompilation \
  --compiler.TracePerformanceWarnings=all \
  <program> 2>&1 | tee compilation.log

⚠️ REQUIRED: Fermi Verification (Every Tool Invocation)

Before running:

• Pre-calculate: Expected # of compilations (5-20 for typical benchmark)
• Smoke test: <launcher> --experimental-options --engine.TraceCompilation -c 'print 1;' → Verify compilation events appear

After running:

• Validate: Expected functions appear in trace? YES / NO
• If NO: STOP - Check if functions are hot enough (increase iterations)
• Save output: tool-outputs/trace-compilation-[benchmark].txt

Gate: All boxes checked? → Proceed to analysis

Key Options

Option	Description
--engine.TraceCompilation	Basic compilation events
--engine.TraceCompilationDetails	Detailed timing
--engine.TraceCompilationPolymorphism	Polymorphic specializations
--engine.CompileOnly=<name>	Filter to specific function

Understanding Output

Successful Compilation

[engine] opt done    root sieve  <tier1>   |Time:    45ms
[engine] opt done    root sieve  <tier2>   |Time:   234ms

Compilation Failure

[engine] opt failed  root sieve  |Reason: Bailout

Invalidation

[engine] opt deopt   root sieve  |Reason: Assumption invalidated

Event Types

Event	Meaning	Action
opt done	Compilation succeeded ✅	Good
opt failed	Compilation failed ❌	Investigate reason
opt deopt	Invalidated ⚠️	Check for deoptimization loops
opt queued	Waiting for compilation	Normal

Tier Levels

Tier	Description	Expected
tier1	First-tier compilation	Fast, basic optimizations
tier2	Full optimization	Slower, maximum optimization

Problem Patterns

Pattern 1: No Compilation Events

Symptom: Function never appears in trace Cause: Not hot enough, or compilation disabled Fix: Check thresholds, verify function is called enough

Pattern 2: Repeated Deopt Cycles

opt done    myFunc  <tier1>
opt deopt   myFunc
opt done    myFunc  <tier1>
opt deopt   myFunc
...repeating...

Cause: Type instability or deoptimization loop Fix: Use detecting-deoptimizations skill

Pattern 3: Compilation Bailout

opt failed  myFunc  |Reason: Bailout

Cause: Code too complex or unsupported pattern Fix: Use detecting-performance-warnings to find barriers

Integration with Other Skills

Finding	Next Skill
No compilations	Check thresholds
Deopt cycles	detecting-deoptimizations
Bailouts	detecting-performance-warnings
Still unclear	analyzing-compiler-graphs

Related Skills

• profiling-with-cpu-sampler - Identify hot functions first
• detecting-performance-warnings - Find barriers
• detecting-deoptimizations - Track deoptimizations
• tracing-inlining-decisions - Inlining behavior

Reference

<launcher> --help:engine | grep -i trace