Update notes with CGSCC information

This doesn't propagate it back via the worklist, but it does tell us
about recursive loops.

src/BoundedTerminationPass.cpp

@@ -1,7 +1,7 @@
 
+#include "llvm/ADT/SCCIterator.h"
 #include "llvm/ADT/StringRef.h"
-#include "llvm/Analysis/CGSCCPassManager.h"
-#include "llvm/Analysis/LazyCallGraph.h"
+#include "llvm/Analysis/CallGraph.h"
 #include "llvm/Analysis/LoopAnalysisManager.h"
 #include "llvm/Analysis/LoopInfo.h"
 #include "llvm/Analysis/ScalarEvolution.h"
@@ -373,15 +373,6 @@ FunctionTerminationPass::run(llvm::Function &F,
 
   llvm::ScalarEvolution &SE = FAM.getResult<llvm::ScalarEvolutionAnalysis>(F);
   llvm::LoopInfo &loop_info = FAM.getResult<llvm::LoopAnalysis>(F);
-  // const auto &outer_result = detect_cgscc_recursion(F, FAM);
-  //
-  // // If this function is part of a recursive call-graph group
-  // // (a non-trivial CGSCC), then we don't do any more analysis.
-  // // This way, we avoid recursing in getResult<Callee>
-  // // for the callees of this function.
-  // if (outer_result.elt >= DoesThisTerminate::Unbounded) {
-  //   return outer_result;
-  // }
 
   std::map<llvm::BasicBlock *, TerminationPassResult> blocks_to_results;
   // SetVector preserves insertion order - which is nice because it makes this
@@ -450,9 +441,38 @@ ModuleTerminationPass::run(llvm::Module &IR, llvm::ModuleAnalysisManager &AM) {
         {&function, FAM.getResult<FunctionTerminationPass>(function)});
   }
 
-  // Step 2 : CGSCC analysis; note recursion up-front.
-  // TODO: This is taking literally forever. No, figuratively forever
-  // auto &call_graph = AM.getResult<llvm::LazyCallGraphAnalysis>(IR);
+  // Step 2 : CGSCC analysis.
+  // Take anything in a recursive group and force it Unknown.
+  // See also NoRecursionCheck in clang-tidy
+  llvm::CallGraph &CG = AM.getResult<llvm::CallGraphAnalysis>(IR);
+  for(llvm::scc_iterator<llvm::CallGraph*> SCCI = llvm::scc_begin(&CG); !SCCI.isAtEnd(); ++SCCI) {
+    if(!SCCI.hasCycle()) {
+      // SCC doesn't have a loop. We don't need to update anything.
+      continue;
+    }
+    // SCC has a loop. Update all functions to note they're mutually recursive.
+    const std::vector<llvm::CallGraphNode *> &nextSCC = *SCCI;
+    TerminationPassResult shared_result = {
+      .elt = DoesThisTerminate::Unknown,
+      .explanation = "part of a call graph that contains a loop: ",
+    };
+    int count = 0;
+    for(llvm::CallGraphNode *node : nextSCC) {
+      const llvm::Function *f = node->getFunction();
+      shared_result.explanation = (shared_result.explanation + llvm::demangle(f->getName()));
+      if(count < nextSCC.size() - 1) {
+        shared_result.explanation += ", ";
+      } else {
+        ++count;
+      }
+    }
+    for(llvm::CallGraphNode *node : nextSCC) {
+      llvm::Function *f = node->getFunction();
+      const auto new_result =  update(per_function_results[f], {shared_result});
+      per_function_results[f] = new_result;
+    }
+  }
+  // TODO
 
   // Step 3 : worklist algorithm on the call graph.
   // TODO: