Compare -O0 vs -O1 vs -O2 vs -O3 Assembly Output

Optimization Levels and Tradeoffs

GCC and Clang -O0 through -O3 and -Os change inlining, vectorization, and alias assumptions. Production servers compile hot paths at -O2 or -O3; debug builds stay at -O0 so breakpoints line up with source.

Flags That Matter

-O2: standard optimizations without aggressive size blowup. -O3: more inlining and vectorization. -ffast-math: relaxes IEEE rules for speed. -g does not disable optimizations.

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• Compare object sizes with size and nm when code bloat appears
• -fomit-frame-pointer speeds x86 but breaks naive stack walks
• Document flags in CI so benchmarks match production
• Use -S to inspect assembly when a loop did not vectorize

Working Through the Exercise

Keep the relevant documentation open while you implement. When your output disagrees with the reference, trace one failing case by hand before changing random lines.

• Trace first: walk one failing input step by step
• Read the manual: skim the official doc for the mechanism named in this task
• Compare baselines: save measurements from the prior step so speedups are honest

Why for this exercise

You will compile the same program at -O0, -O2, and -O3 and compare runtime and binary size. This exercise asks you to attribute one speedup to a specific optimization visible in assembly.