LLVM Passes

Purpose

Guide agents through writing LLVM optimization passes with the New Pass Manager: FunctionPass and ModulePass structure, PassPluginLibraryInfo registration, running via opt -load-pass-plugin, common analysis utilities (DominatorTree, LoopInfo, AliasAnalysis), IR modification patterns, llvm-lit testing, and debugging with opt -print-after-all.

When to Use

• Adding a custom optimization to an LLVM-based compiler
• Writing an IR transformation pass (inlining, DCE, custom lowering)
• Analyzing control flow with dominator trees or loop info
• Testing passes with FileCheck and llvm-lit
• Debugging pass ordering and IR corruption
• Integrating passes into Clang via plugin

Workflow

1. New Pass Manager architecture