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

bash

# 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

code

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

Compilation Failure

code

[engine] opt failed  root sieve  |Reason: Bailout

Invalidation

code

[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

code

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

code

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

bash

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