The trust you place is based on mathematical evidence for the soundness of the compiler. The compiler is thus trustworthy, based on formal arguments, as opposed to informal arguments (such as "we did some testing" or "no bugs are were reported").
Going back to Kant, formal arguments in this sense are a priori knowledge -- knowledge that is in some sense objective, and independent from any observer making empirical measurements (as opposed to a posteriori, or experimental, knowledge).
Going back to Kant, formal arguments in this sense are a priori knowledge -- knowledge that is in some sense objective, and independent from any observer making empirical measurements (as opposed to a posteriori, or experimental, knowledge).