FCI: API for fallthrough BasicBlocks

The `FunctionCallIdentification` pass now has an API to get the
fallthrough basic block of a function call basic block and to check
whether a certain basic block/address is the fallthrough of a function
call.

functioncallidentification.cpp

@@ -24,6 +24,8 @@ bool FunctionCallIdentification::runOnFunction(llvm::Function &F) {
 
   auto &GCBI = getAnalysis<GeneratedCodeBasicInfo>();
 
+  FallthroughAddresses.clear();
+
   // Create function call marker
   // TODO: we could factor this out
   Module *M = F.getParent();
@@ -216,6 +218,8 @@ bool FunctionCallIdentification::runOnFunction(llvm::Function &F) {
         LinkRegister
       };
 
+      FallthroughAddresses.insert(ReturnPC);
+
       // If the instruction before the terminator is a call to exitTB, inject
       // the call to function_call before it, so it doesn't get purged
       auto It = Terminator->getIterator();