One way to understand and debug IR optimization process is to visualize Control Flow Graphs (CFGs) before and after optimization and compare them. However, comparing the CFGs can be challenging since they can vary significantly. LLVM-FLOW, an open-source interactive CFG visualization web app, is developed to ease the difficulty by highlighting the same components in two graphs. With this tool, users can easily find corresponding nodes in another graph by clicking the highlighted node. LLVM-FLOW is a useful tool not only for experienced LLVM developers seeking to better understand the IR flow when writing custom passes, but also for newcomers to the LLVM ecosystem who wish to study the behavior of IR patterns.