1. A compiling method for compiling a source code file in a code base, the method comprising: compiling the source code file in the code base using an optimizing compiler specialized to the code base and accordingly generating an intermediate representation; analyzing the intermediate representation to obtain and store characteristics of the code base, wherein the intermediate representation is not itself further modified; recompiling the code base with the optimizing compiler using the characteristics of the code base, obtaining reusable resources from the characteristics of the code base; and optimizing compiled code using the reusable resources for use in the recompiling step; and rebuilding the optimized compiler according to (i) the reusable resources for use in the recompiling step, (ii) transformation specifications, which specify a pattern that matches a common subsequence and a library call that is used to replace the common subsequence, and (iii) guard code, which is used to skip a given optimization pass.