Fix PR4834, a tricky case where the inliner would resolve an

indirect function pointer, inline it, then go to delete the body.
The problem is that the callgraph had other references to the function,
though the inliner had no way to know it, so we got a dangling pointer
and an invalid iterator out of the deal.

The fix to this is pretty simple: stop the inliner from deleting the
function by knowing that there are references to it.  Do this by making
CallGraphNodes contain a refcount.  This requires moving deletion of 
available_externally functions to the module-level cleanup sweep where
it belongs.

llvm-svn: 80533

include/llvm/Analysis/CallGraph.h

@@ -77,7 +77,7 @@ protected:
 public:
   static char ID; // Class identification, replacement for typeinfo
   //===---------------------------------------------------------------------
-  // Accessors...
+  // Accessors.
   //
   typedef FunctionMapTy::iterator iterator;
   typedef FunctionMapTy::const_iterator const_iterator;
@@ -136,7 +136,7 @@ public:
   CallGraphNode *getOrInsertFunction(const Function *F);
 
   //===---------------------------------------------------------------------
-  // Pass infrastructure interface glue code...
+  // Pass infrastructure interface glue code.
   //
 protected:
   CallGraph() {}
@@ -164,18 +164,30 @@ class CallGraphNode {
   typedef std::pair<CallSite,CallGraphNode*> CallRecord;
   std::vector<CallRecord> CalledFunctions;
   
-  CallGraphNode(const CallGraphNode &);           // Do not implement
+  /// NumReferences - This is the number of times that this CallGraphNode occurs
+  /// in the CalledFunctions array of this or other CallGraphNodes.
+  unsigned NumReferences;
+
+  CallGraphNode(const CallGraphNode &);            // DO NOT IMPLEMENT
+  void operator=(const CallGraphNode &);           // DO NOT IMPLEMENT
+  
+  void DropRef() { --NumReferences; }
+  void AddRef() { ++NumReferences; }
 public:
   typedef std::vector<CallRecord> CalledFunctionsVector;
 
+  
+  // CallGraphNode ctor - Create a node for the specified function.
+  inline CallGraphNode(Function *f) : F(f), NumReferences(0) {}
+  
   //===---------------------------------------------------------------------
-  // Accessor methods...
+  // Accessor methods.
   //
 
   typedef std::vector<CallRecord>::iterator iterator;
   typedef std::vector<CallRecord>::const_iterator const_iterator;
 
-  // getFunction - Return the function that this call graph node represents...
+  // getFunction - Return the function that this call graph node represents.
   Function *getFunction() const { return F; }
 
   inline iterator begin() { return CalledFunctions.begin(); }
@@ -185,9 +197,14 @@ public:
   inline bool empty() const { return CalledFunctions.empty(); }
   inline unsigned size() const { return (unsigned)CalledFunctions.size(); }
 
-  // Subscripting operator - Return the i'th called function...
+  /// getNumReferences - Return the number of other CallGraphNodes in this
+  /// CallGraph that reference this node in their callee list.
+  unsigned getNumReferences() const { return NumReferences; }
+  
+  // Subscripting operator - Return the i'th called function.
   //
   CallGraphNode *operator[](unsigned i) const {
+    assert(i < CalledFunctions.size() && "Invalid index");
     return CalledFunctions[i].second;
   }
 
@@ -204,7 +221,10 @@ public:
   /// removeAllCalledFunctions - As the name implies, this removes all edges
   /// from this CallGraphNode to any functions it calls.
   void removeAllCalledFunctions() {
-    CalledFunctions.clear();
+    while (!CalledFunctions.empty()) {
+      CalledFunctions.back().second->DropRef();
+      CalledFunctions.pop_back();
+    }
   }
   
   /// stealCalledFunctionsFrom - Move all the callee information from N to this
@@ -220,6 +240,7 @@ public:
   /// one.
   void addCalledFunction(CallSite CS, CallGraphNode *M) {
     CalledFunctions.push_back(std::make_pair(CS, M));
+    M->AddRef();
   }
 
   /// removeCallEdgeFor - This method removes the edge in the node for the
@@ -240,11 +261,6 @@ public:
   /// New CallSite instead.  Note that this method takes linear time, so it
   /// should be used sparingly.
   void replaceCallSite(CallSite Old, CallSite New, CallGraphNode *NewCallee);
-
-  friend class CallGraph;
-
-  // CallGraphNode ctor - Create a node for the specified function.
-  inline CallGraphNode(Function *f) : F(f) {}
 };
 
 //===----------------------------------------------------------------------===//

lib/Analysis/IPA/CallGraph.cpp

@@ -53,7 +53,7 @@ public:
     CallsExternalNode = new CallGraphNode(0);
     Root = 0;
   
-    // Add every function to the call graph...
+    // Add every function to the call graph.
     for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I)
       addToCallGraph(I);
   
@@ -169,13 +169,13 @@ void CallGraph::initialize(Module &M) {
 }
 
 void CallGraph::destroy() {
-  if (!FunctionMap.empty()) {
+  if (FunctionMap.empty()) return;
+  
   for (FunctionMapTy::iterator I = FunctionMap.begin(), E = FunctionMap.end();
       I != E; ++I)
     delete I->second;
   FunctionMap.clear();
 }
-}
 
 void CallGraph::print(raw_ostream &OS, Module*) const {
   for (CallGraph::const_iterator I = begin(), E = end(); I != E; ++I)
@@ -219,10 +219,11 @@ CallGraphNode *CallGraph::getOrInsertFunction(const Function *F) {
 
 void CallGraphNode::print(raw_ostream &OS) const {
   if (Function *F = getFunction())
-    OS << "Call graph node for function: '" << F->getName()
-       << "'<<0x" << this << ">>\n";
+    OS << "Call graph node for function: '" << F->getName() << "'";
   else
-    OS << "Call graph node <<null function: 0x" << this << ">>:\n";
+    OS << "Call graph node <<null function>>";
+  
+  OS << "<<0x" << this << ">>  #uses=" << getNumReferences() << '\n';
 
   for (const_iterator I = begin(), E = end(); I != E; ++I)
     if (Function *FI = I->second->getFunction())
@@ -241,7 +242,9 @@ void CallGraphNode::removeCallEdgeFor(CallSite CS) {
   for (CalledFunctionsVector::iterator I = CalledFunctions.begin(); ; ++I) {
     assert(I != CalledFunctions.end() && "Cannot find callsite to remove!");
     if (I->first == CS) {
-      CalledFunctions.erase(I);
+      I->second->DropRef();
+      *I = CalledFunctions.back();
+      CalledFunctions.pop_back();
       return;
     }
   }
@@ -254,6 +257,7 @@ void CallGraphNode::removeCallEdgeFor(CallSite CS) {
 void CallGraphNode::removeAnyCallEdgeTo(CallGraphNode *Callee) {
   for (unsigned i = 0, e = CalledFunctions.size(); i != e; ++i)
     if (CalledFunctions[i].second == Callee) {
+      Callee->DropRef();
       CalledFunctions[i] = CalledFunctions.back();
       CalledFunctions.pop_back();
       --i; --e;
@@ -266,8 +270,10 @@ void CallGraphNode::removeOneAbstractEdgeTo(CallGraphNode *Callee) {
   for (CalledFunctionsVector::iterator I = CalledFunctions.begin(); ; ++I) {
     assert(I != CalledFunctions.end() && "Cannot find callee to remove!");
     CallRecord &CR = *I;
-    if (CR.second == Callee && !CR.first.getInstruction()) {
-      CalledFunctions.erase(I);
+    if (CR.second == Callee && CR.first.getInstruction() == 0) {
+      Callee->DropRef();
+      *I = CalledFunctions.back();
+      CalledFunctions.pop_back();
       return;
     }
   }
@@ -285,8 +291,11 @@ void CallGraphNode::replaceCallSite(CallSite Old, CallSite New,
       
       // If the callee is changing, not just the callsite, then update it as
       // well.
-      if (NewCallee)
+      if (NewCallee) {
+        I->second->DropRef();
         I->second = NewCallee;
+        I->second->AddRef();
+      }
       return;
     }
   }

lib/Transforms/IPO/Inliner.cpp

@@ -293,10 +293,12 @@ bool Inliner::runOnSCC(std::vector<CallGraphNode*> &SCC) {
       
       // If we inlined the last possible call site to the function, delete the
       // function body now.
-      if (Callee->use_empty() && 
-          (Callee->hasLocalLinkage() ||
-           Callee->hasAvailableExternallyLinkage()) &&
-          !SCCFunctions.count(Callee)) {
+      if (Callee->use_empty() && Callee->hasLocalLinkage() &&
+          !SCCFunctions.count(Callee) &&
+          // The function may be apparently dead, but if there are indirect
+          // callgraph references to the node, we cannot delete it yet, this
+          // could invalidate the CGSCC iterator.
+          CG[Callee]->getNumReferences() == 0) {
         DEBUG(errs() << "    -> Deleting dead function: "
               << Callee->getName() << "\n");
         CallGraphNode *CalleeNode = CG[Callee];
@@ -353,7 +355,7 @@ bool Inliner::removeDeadFunctions(CallGraph &CG,
   // from the program.  Insert the dead ones in the FunctionsToRemove set.
   for (CallGraph::iterator I = CG.begin(), E = CG.end(); I != E; ++I) {
     CallGraphNode *CGN = I->second;
-    if (CGN == 0 || CGN->getFunction() == 0)
+    if (CGN->getFunction() == 0)
       continue;
     
     Function *F = CGN->getFunction();
@@ -364,7 +366,8 @@ bool Inliner::removeDeadFunctions(CallGraph &CG,
 
     if (DNR && DNR->count(F))
       continue;
-    if (!F->hasLinkOnceLinkage() && !F->hasLocalLinkage())
+    if (!F->hasLinkOnceLinkage() && !F->hasLocalLinkage() &&
+        !F->hasAvailableExternallyLinkage())
       continue;
     if (!F->use_empty())
       continue;

test/Transforms/Inline/indirect_resolve.ll

@@ -0,0 +1,16 @@
+; RUN: llvm-as < %s | opt -inline | llvm-dis
+; PR4834
+
+define i32 @main() {
+  %funcall1_ = call fastcc i32 ()* ()* @f1()
+  %executecommandptr1_ = call i32 %funcall1_()
+  ret i32 %executecommandptr1_
+}
+
+define internal fastcc i32 ()* @f1() nounwind readnone {
+  ret i32 ()* @f2
+}
+
+define internal i32 @f2() nounwind readnone {
+  ret i32 1
+}