Q3: What is the JIT Compiler and how does Tiered Compilation work in HotSpot JVM?
The Just-In-Time (JIT) Compiler is a JVM subsystem that improves runtime performance by compiling frequently executed bytecode sequences ('hot spots') directly into native machine code at runtime. HotSpot uses Tiered Compilation:
- Tier 0: Interpreted bytecode execution.
- Tiers 1-3 (C1 Compiler / Client Compiler): Fast compilation with basic optimizations.
- Tier 4 (C2 Compiler / Server Compiler): Heavy profile-guided optimizations (inlining, escape analysis, loop unrolling).
Key Takeaways
- JIT translates hot bytecode paths into native machine code at runtime.
- Tiered compilation balances rapid startup time (C1) with high peak performance (C2).
Knowledge Check
What is the primary role of the C2 compiler in HotSpot Tiered Compilation?