PassManagerBuilder.h

### PassManagerBuilder.h C++ Header File Usage and Information The `PassManagerBuilder` class, defined within the LLVM project’s infrastructure, serves as an essential component for constructing pass managers that control optimization passes during code compilation or transformation processes[^4]. This utility facilitates setting up both function-pass managers (for per-function optimizations) and module-pass managers (for whole-module transformations). #### Key Features of PassManagerBuilder - **Optimization Level Configuration**: Allows specifying different levels of optimization through parameters like `-O0`, `-O1`, etc., which dictate how aggressively the compiler should optimize. - **Target Machine Integration**: Supports integration with target-specific configurations to ensure generated machine instructions are optimized according to hardware capabilities. - **Customization Options**: Provides flexibility by enabling users to add custom passes at various stages of the pipeline using methods such as `addLibraryInfo`. #### Example Code Demonstrating Basic Use Cases Below demonstrates initializing a basic setup where one can define specific behaviors before running any given set of passes: ```cpp #include "llvm/IR/LegacyPassManager.h" #include "llvm/Transforms/IPO/PassManagerBuilder.h" using namespace llvm; void configureAndRunPasses(Module &M) { LegacyPassManager MPM; PassManagerBuilder Builder; // Set Optimization level here (-O0, -O1, ...) Builder.OptLevel = 2; // Add default optimizations based on selected OptLevel Builder.populateModulePassManager(MPM); // Execute all scheduled passes over input Module 'M' MPM.run(M); } ``` In this example, after including necessary headers from LLVM's API, a new instance of `LegacyPassManager` named `MPM` gets created alongside configuring options via `PassManagerBuilder`. Finally, executing these settings against some provided `Module` object results in applying chosen transformations effectively. --related questions-- 1. How does integrating TargetMachine into PassManager affect performance? 2. What other customization points exist beyond adding library info when working with PassManagerBuilder? 3. Can you provide more detailed examples showing advanced use cases involving multiple types of pass managers simultaneously? 4. Is there support for parallel execution models while managing several modules concurrently under single management structures? 5. Are there alternative APIs available outside LLVM offering similar functionalities but perhaps simpler interfaces?