Use __restrict__ Pointer to Enable Alias Analysis Optimization

Promise Non-Overlapping Pointers

C99 restrict tells the compiler two pointer parameters do not alias the same memory, enabling aggressive load/store reordering and vectorization. Violating the promise is undefined behavior. BLAS kernels and memcpy implementations use restrict heavily.

Example Kernel

Separate read and write buffers with restrict so the compiler can vectorize the loop without runtime alias checks.

cCopy
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• -fno-strict-aliasing disables type-based alias analysis; avoid in hot code
• __restrict__ is the GCC spelling accepted in C++
• restrict on struct members is C99 only in limited cases
• Compare assembly with and without restrict on the same loop

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 mark a hot loop with restrict and show improved vectorization or fewer memory barriers in assembly. This exercise asks you to document the aliasing assumption.