The default setting of Automatic generates more efficient code by avoiding computing the same result more than once:

When the optimization level is reduced, less efficient code is generated:

This generates C code and links it back in for execution:

This is a larger example that demonstrates the speed advantages of C code generation:

The default operation runs more slowly:

Listable compiled functions can execute in parallel using threads:

This shows the operation running sequentially:

Typically, $ProcessorCount is used to determine how many threads to be used:

You can combine parallel operations with C code generation to get even faster operation:

This creates a listable compiled function:

It operates on a single input in normal fashion:

When the arguments include a list that does not match the input specification, it threads over that argument:

If there is a branch, listability needs a function to be defined, as shown below using Function:

A listable compiled function is equivalent but executes faster:

A listable compiled function can run in parallel, giving an acceleration on multicore machines:

Using the listable attribute is typically faster than invoking CompiledFunction many times:

Using parallelization can give an even greater speedup:

The results are identical:

A detailed plot of the basins of attraction for Newton's method for :

Typically, integer arithmetic overflow is caught and the computation switches to use bignums:

Turning off overflow checking makes for faster execution, but the result can be incorrect: