Remove Vectorization Barriers and Use Compiler Hints

Help the Compiler SIMD

Auto-vectorization needs provably independent iterations, aligned pointers, and no function calls in the inner loop. #pragma GCC ivdep, clang loop vectorize(enable), and OpenMP simd directives remove assumed dependencies the compiler cannot prove.

Vectorizable Loop Shape

Simple counting loop, no backward dependencies, stride-one access on arrays.

cCopy
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• -fopt-info-vec prints why vectorization failed
• __attribute__((aligned(32))) helps AVX loads
• restrict plus ivdep often unlocks SIMD together
• Compare scalar vs vector assembly with objdump -d -Mintel

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 add pragma or attribute hints to vectorize a loop and verify SIMD instructions in assembly. This exercise asks you to report speedup and name the SIMD width used.

Document one invariant you will assert in tests and how you would detect its violation from observable symptoms.