Compilers can easily runtime-detect the size and shape of the problem, and run different code for different problem sizes. Many already do for loop-unrolling.

Compilers can easily runtime-detect the size and shape of the problem, and run different code for different problem sizes. Many already do for loop-unrolling. Ie. if you memcpy 2 bytes, they won't even branch into the fancy SIMD version. This would just be an extension of that. If the code creates and uses a linked list, yet the list is 1M items long and being accessed entirely by index, branch to a different version of the code which uses an array, etc.