Learning instrumentations in the new PassManager

PassManager and AnalysisManager in LLVM are complicated pieces of software. They manage interactions between hundreds of Passes and analyses, and it can be a challenge when we try to diagnose a problem caused by them. In addition, it's really common for a compiler engineer to fix crashes in the compiler or miscompilation bugs. In those scenarios, useful instrumentation tools that provide insights to Passes and the Pass pipeline can greatly improve the productivity of fixing those problems. Fortunately, LLVM has already provided many of those tools.

Miscompilation

Miscompilation bugs usually refer to logical issues in the compiled program, which were introduced by compilers. For example, an overly aggressive compiler optimization removes certain loops that shouldn't be removed, causing the compiled software to malfunction, or mistakenly reorder memory barriers and create race conditions in the generated code.

We will...