Compiled Away

Understanding compiler optimizations and undefined behavior in C++

This medium-difficulty question tests your ability to reason about what C++ code actually does at runtime, rather than what it appears to do on first read. It probes understanding of compiler optimizations, undefined behavior, and the contract between the language spec and real-world execution.

To answer correctly, you need to trace through the code carefully, identify whether any operations invoke undefined behavior, and predict what a standards-compliant compiler is entitled to do. Interviewers at systems-focused firms—particularly those building low-latency infrastructure—use questions like this to assess whether you understand the boundaries between portable C++ and platform-specific assumptions.

• Undefined behavior and the "as-if" rule
• Compiler optimization and dead-code elimination
• Order of evaluation and sequence points
• Reading uninitialized memory