diff --git a/llvm/lib/Transforms/IPO/Attributor.cpp b/llvm/lib/Transforms/IPO/Attributor.cpp
--- a/llvm/lib/Transforms/IPO/Attributor.cpp
+++ b/llvm/lib/Transforms/IPO/Attributor.cpp
@@ -1350,34 +1350,27 @@
 // endless loop
 // FIXME: Any cycle is regarded as endless loop for now.
 //        We have to allow some patterns.
-static bool containsPossiblyEndlessLoop(Function &F) {
-  return containsCycle(F);
+static bool containsPossiblyEndlessLoop(Function *F) {
+  return !F || !F->hasExactDefinition() || containsCycle(*F);
 }
 
 struct AAWillReturnImpl : public AAWillReturn {
   AAWillReturnImpl(const IRPosition &IRP) : AAWillReturn(IRP) {}
 
-  /// See AbstractAttribute::getAsStr()
-  const std::string getAsStr() const override {
-    return getAssumed() ? "willreturn" : "may-noreturn";
-  }
-};
-
-struct AAWillReturnFunction final : AAWillReturnImpl {
-  AAWillReturnFunction(const IRPosition &IRP) : AAWillReturnImpl(IRP) {}
-
   /// See AbstractAttribute::initialize(...).
   void initialize(Attributor &A) override {
-    Function &F = *getAnchorScope();
+    if (hasAttr({Attribute::WillReturn})) {
+      indicateOptimisticFixpoint();
+      return;
+    }
 
+    Function *F = getAssociatedFunction();
     if (containsPossiblyEndlessLoop(F))
       indicatePessimisticFixpoint();
   }
 
   /// See AbstractAttribute::updateImpl(...).
   ChangeStatus updateImpl(Attributor &A) override {
-    // The map from instruction opcodes to those instructions in the function.
-
     auto CheckForWillReturn = [&](Instruction &I) {
       ImmutableCallSite ICS(&I);
       if (ICS.hasFnAttr(Attribute::WillReturn))
@@ -1402,12 +1395,25 @@
     return ChangeStatus::UNCHANGED;
   }
 
+  /// See AbstractAttribute::getAsStr()
+  const std::string getAsStr() const override {
+    return getAssumed() ? "willreturn" : "may-noreturn";
+  }
+};
+
+struct AAWillReturnFunction final : AAWillReturnImpl {
+  AAWillReturnFunction(const IRPosition &IRP) : AAWillReturnImpl(IRP) {}
+
   /// See AbstractAttribute::trackStatistics()
-  void trackStatistics() const override { STATS_DECLTRACK_FN_ATTR(norecurse) }
+  void trackStatistics() const override { STATS_DECLTRACK_FN_ATTR(willreturn) }
 };
 
-/// WillReturn attribute deduction for a call sites.
-using AAWillReturnCallSite = AAWillReturnFunction;
+struct AAWillReturnCallSite final : AAWillReturnImpl {
+  AAWillReturnCallSite(const IRPosition &IRP) : AAWillReturnImpl(IRP) {}
+
+  /// See AbstractAttribute::trackStatistics()
+  void trackStatistics() const override { STATS_DECLTRACK_CS_ATTR(willreturn) }
+};
 
 /// ------------------------ NoAlias Argument Attribute ------------------------