Pass and Pass Manager

LLVM's Pass infrastructure is one of the many important features of the LLVM system. There are a number of analysis and optimization passes that can be run using this infrastructure. The starting point for LLVM passes is the Pass class, which is a superclass of all the passes. We need to inherit from some predefined subclasses taking into account what our pass is going to implement.

• ModulePass: This is the most general superclass. By inheriting this class we allow the entire module to be analyzed at once. The functions within the module may not be referred to in a particular order. To use it, write a subclass that inherits from the ModulePass subclass and overloads the runOnModule function.

  Note

  Before going ahead with the discussion of other Pass classes, let's look into the three virtual methods that the Pass classes override:

  • doInitialization: This is meant to do initialization stuff that does not depend on the current function being processed.
  • runOn{Passtype...