CPP Performance Optimization & Profiling 3

Question 1

What does the `-O2` flag passed to g++ primarily enable?

Accepted Answer

A standard set of optimizations that do not involve speed-space tradeoffs

Answer

-O2 enables most speed optimizations that don't significantly increase code size, such as inlining, loop optimizations, and common subexpression elimination.

Question 2

Which technique compiles each translation unit with optimization metadata so the linker can optimize across module boundaries?

Accepted Answer

Link-Time Optimization (LTO)

Answer

LTO (enabled with -flto in GCC/Clang) defers full optimization to link time, allowing inlining and analysis across object file boundaries.

Question 3

When using `std::vector`, which operation is guaranteed O(1) amortized but may trigger a reallocation?

Accepted Answer

push_back()

Answer

push_back() is amortized O(1) because reallocation doubles capacity, but occasionally triggers an O(n) copy/move of all elements.

Question 4

What is 'profile-guided optimization' (PGO)?

Accepted Answer

A two-phase process: compile, run with representative input, recompile using profiling data

Answer

PGO instruments a first build, runs it to collect branch and frequency data, then uses that data in a second build to make better optimization decisions.

Question 5

Which of the following best describes 'instruction-level parallelism' (ILP)?

Accepted Answer

Executing multiple independent instructions simultaneously within a single core pipeline

Answer

ILP refers to the CPU's ability to execute multiple independent instructions simultaneously using techniques like out-of-order execution and superscalar pipelines.

(CPP) C++ Programming Professional Certificate Practice Test

(CPP) C++ Programming Professional Certificate Practice Test

CPP Performance Optimization & Profiling 3