Let PassBuilder Expose PassInstrumentationCallbacks

[aqjune]

Summary

This is an effort to allowing external libraries register their own pass instrumentation during their llvmGetPassPluginInfo() calls.

By exposing this through the added getPIC(), now a pass writer can do something like this:

extern "C" ::llvm::PassPluginLibraryInfo LLVM_ATTRIBUTE_WEAK
llvmGetPassPluginInfo() {
  return {
    ..,
    [](llvm::PassBuilder &PB) {
      PB.getPIC()->registerAfterPassCallback(move(f));
    }
  };
}

[fedor.sergeev]

Overall I'm fine with this.
Bikeshedding-wise, getPIC seems to be overly cryptic to me.
Do you believe full name getPassInstrumentationCallbacks is too much?

Also, please, add at least one test.
I would start with llvm/unittests/IR/PassBuilderCallbacksTest.cpp

[aqjune]

Sorry for my delay.
I updated the function name & added a unit test.

[aqjune]

ping

[fedor.sergeev]

LGTM.

llvm/include/llvm/Passes/PassBuilder.h

635

nit: "to add pass instrumentation" -> "to register pass instrumentation callbacks."

[aqjune]

• Address a comment

llvm/include/llvm/Passes/PassBuilder.h

public:
   }
 
   /// Add PGOInstrumenation passes for O0 only.
   void addPGOInstrPassesForO0(ModulePassManager &MPM, bool DebugLogging,
                               bool RunProfileGen, bool IsCS,
                               std::string ProfileFile,
                               std::string ProfileRemappingFile);
 
+
+  /// Returns PIC. External libraries can use this to register pass
+  /// instrumentation callbacks.
+  PassInstrumentationCallbacks *getPassInstrumentationCallbacks() const {
+    return PIC;
+  }
+
 private:
   static Optional<std::vector<PipelineElement>>
   parsePipelineText(StringRef Text);
 
   Error parseModulePass(ModulePassManager &MPM, const PipelineElement &E,
                         bool VerifyEachPass, bool DebugLogging);
   Error parseCGSCCPass(CGSCCPassManager &CGPM, const PipelineElement &E,
                        bool VerifyEachPass, bool DebugLogging);

llvm/unittests/IR/PassBuilderCallbacksTest.cpp

PassBuilderCallbacksTest()
                   "  br i1 %cmp, label %exit, label %loop\n"
                   "exit:\n"
                   "  ret void\n"
                   "}\n")),
         CallbacksHandle(),
         PB(nullptr, PipelineTuningOptions(), None, &CallbacksHandle.Callbacks),
         PM(true), LAM(true), FAM(true), CGAM(true), AM(true) {
 
+    EXPECT_TRUE(&CallbacksHandle.Callbacks ==
+                PB.getPassInstrumentationCallbacks());
+
     /// Register a callback for analysis registration.
     ///
     /// The callback is a function taking a reference to an AnalyisManager
     /// object. When called, the callee gets to register its own analyses with
     /// this PassBuilder instance.
     PB.registerAnalysisRegistrationCallback([this](AnalysisManagerT &AM) {
       // Register our mock analysis
       AM.registerPass([this] { return AnalysisHandle.getAnalysis(); });