Let PassBuilder Expose PassInstrumentationCallbacks

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));
    }
  };
}
```

Reviewers: chandlerc, philip.pfaffe, fedor.sergeev

Reviewed By: fedor.sergeev

Subscribers: llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D71086

1 files changed, 3 insertions, 0 deletions

diff --git a/llvm/unittests/IR/PassBuilderCallbacksTest.cpp b/llvm/unittests/IR/PassBuilderCallbacksTest.cpp
index 7306257851a..3f800b308e2 100644
--- a/llvm/unittests/IR/PassBuilderCallbacksTest.cpp
+++ b/llvm/unittests/IR/PassBuilderCallbacksTest.cpp
@@ -418,6 +418,9 @@ protected:
         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