Getting llvm::LoopInfo from (non-LLVM) code?

Question

For the development of my own Pass I want to write unit tests - i have lots of 'pure' helper methods, so they seem ideal candidates for unit test. But some of them require an instance of llvm::LoopInfo as an argument.

In my (Function-)Pass I just use

void getAnalysisUsage(llvm::AnalysisUsage &AU) const override {
    AU.setPreservesCFG();
    AU.addRequired<llvm::LoopInfoWrapperPass>();
}
...
llvm::LoopInfo &loopInfo = getAnalysis<LoopInfoWrapperPass>(F).getLoopInfo();

to get this information object.

In my unit test I currently parse my llvm::Function void foo() (that I want to run my analysis on) from disk like this:

llvm::SMDiagnostic Err;
llvm::LLVMContext Context;
std::unique_ptr<llvm::Module> module(parseIRFile(my_bc_filename, Err, Context));
llvm::Function* foo = module.operator*().getFunction("foo");

to finalize my test I would have to fill in following stub:

llvm::LoopInfo& = /*run LoopInfoWrapperPass on foo and return LoopInfo element */;

My first attempts were based on using the PassManager<Function> (in Header "llvm/IR/PassManager.h"), AnalysisManager<Function>, and the class LoopInfoWrapperPass, but I couldn't find any example usage online for LLVM 4.0 - and older examples seemed to be using a previous version of PassManager, and I did not see how to make use of the LegacyPassManager. I tried to look into the sources for PassManager but could not make enough sense of the typedefs and template arguments (and they are increasing my irrational dislike for C++ as a language).

How do I fill in that stub? How do I call this Analysis Pass (and get LoopInfo) in my plain C++ code?

PS: There are more passes other than LoopInfoWrapperPass I need to use, but I'm assuming the way should be transferable to any Analysis Pass.

PPS: I'm using googletest as a unit test framework, with a CMake build configuration that makes the unit tests their own target, and I'm building my Pass out-of-tree against binary libs of LLVM 4.0.1, if any of that is somehow relevant.

Answer 1

I am not sure how you have your unit tests structured, but looking around in the LLVM source tree is a good idea.

One example can be found in CFGTest.cpp here. You need to create the PassManager and the pipeline yourself. From my short experience on this, it works well for small tests, but once you need anything bigger or pass data in/out it's really restricting, since the LoopInfo data have only meaning within the pipeline (aka runOn() methods and friends).

Otherwise, you might want to opt (no pun intended) for the simpler, IMHO, method of creating the set of the required analysis yourself (only dominators in the case of LoopInfo) without using the pass manager infrastructure. An example of this can be seen here.

Hope this helps.