All of the tests are written so that a compiler can, in principle, transform the OOP code into the C-style code. Many programmers experiment with the style and find it expressive, only to be shocked at the performance penalty. Some give up on the style entirely. The Four Kernels Max measures how well a compiler inlines a simple conditional.
Matrix measures how well a compiler propagates constants and hoists simple invariants.
Iterator measures how well a compiler inlines short-lived small objects. Complex measures how well a compiler eliminates temporaries.