The point of most of the optimizations mentioned in the article is not to make programs run faster; e.g. any competent programmer can hoist constant functions o

The point of most of the optimizations mentioned in the article is not to make programs run faster; e.g. any competent programmer can hoist constant functions out of a for loop himself, but knowing that the compiler will do this allows you to write cleaner code. (This does not apply to e.g. auto-vectorization, which replaces 'x[0] = y[0] * z[0]; x[1] = y[1] * z[1]; ...' by a single (SSE?) instructions which calculates all of that at once. Such instructions are much faster and would require dropping down to assembly without a good optimizer.)