Index: llvm/include/llvm/Transforms/IPO/Attributor.h
===================================================================
--- llvm/include/llvm/Transforms/IPO/Attributor.h
+++ llvm/include/llvm/Transforms/IPO/Attributor.h
@@ -1682,6 +1682,29 @@
   static const char ID;
 };
 
+/// An abstract attribute for undefinedbehavior.
+struct AAUndefinedBehavior
+    : public StateWrapper<BooleanState, AbstractAttribute>,
+      public IRPosition {
+  AAUndefinedBehavior(const IRPosition &IRP) : IRPosition(IRP) {}
+
+  /// Return true if "undefinedbehavior" is assumed.
+  bool isAssumedAAUndefinedBehavior() const { return true; }
+
+  /// Return true if "undefinedbehavior" is known.
+  bool isKnownAAUndefinedBehavior() const { return false; }
+
+  /// Return an IR position, see struct IRPosition.
+  const IRPosition &getIRPosition() const override { return *this; }
+
+  /// Create an abstract attribute view for the position \p IRP.
+  static AAUndefinedBehavior &createForPosition(const IRPosition &IRP,
+                                                Attributor &A);
+
+  /// Unique ID (due to the unique address)
+  static const char ID;
+};
+
 /// An abstract interface to determine reachability of point A to B.
 struct AAReachability : public StateWrapper<BooleanState, AbstractAttribute>,
                         public IRPosition {
Index: llvm/lib/Transforms/IPO/Attributor.cpp
===================================================================
--- llvm/lib/Transforms/IPO/Attributor.cpp
+++ llvm/lib/Transforms/IPO/Attributor.cpp
@@ -1963,6 +1963,65 @@
   void trackStatistics() const override { STATS_DECLTRACK_CS_ATTR(norecurse); }
 };
 
+/// -------------------- Undefined-Behavior Attributes ------------------------
+
+struct AAUndefinedBehaviorImpl : public AAUndefinedBehavior {
+  AAUndefinedBehaviorImpl(const IRPosition &IRP) : AAUndefinedBehavior(IRP) {}
+
+  /// See AbstractAttribute::initialize(...).
+  void initialize(Attributor &A) override {
+    AAUndefinedBehavior::initialize(A);
+
+    auto HandleLoadInstruction = [&](Instruction &I) {
+      // TODO: Do something for every load instruction...
+      IRPosition IPos = IRPosition::callsite_function(ImmutableCallSite(&I));
+      return true;
+    };
+    A.checkForAllInstructions(HandleLoadInstruction, *this,
+                              {Instruction::Load});
+  }
+
+  /// See AbstractAttribute::updateImpl(...).
+  ChangeStatus updateImpl(Attributor &A) override {
+    return indicatePessimisticFixpoint();
+  }
+
+  /// See AbstractAttribute::getAsStr()
+  const std::string getAsStr() const override {
+    return getAssumed() ? "undefined-behavior" : "no-ub";
+  }
+};
+
+struct AAUndefinedBehaviorFunction final : AAUndefinedBehaviorImpl {
+  AAUndefinedBehaviorFunction(const IRPosition &IRP)
+      : AAUndefinedBehaviorImpl(IRP) {}
+
+  /// See AbstractAttribute::trackStatistics()
+  void trackStatistics() const override {
+    STATS_DECLTRACK_CS_ATTR(undefinedbehavior)
+  }
+};
+
+struct AAUndefinedBehaviorCallSite final : AAUndefinedBehaviorImpl {
+  AAUndefinedBehaviorCallSite(const IRPosition &IRP)
+      : AAUndefinedBehaviorImpl(IRP) {}
+
+  /// See AbstractAttribute::initialize(...).
+  void initialize(Attributor &A) override {
+    AAUndefinedBehaviorImpl::initialize(A);
+  }
+
+  /// See AbstractAttribute::updateImpl(...).
+  ChangeStatus updateImpl(Attributor &A) override {
+    return indicatePessimisticFixpoint();
+  }
+
+  /// See AbstractAttribute::trackStatistics()
+  void trackStatistics() const override {
+    STATS_DECLTRACK_CS_ATTR(undefinedbehavior)
+  }
+};
+
 /// ------------------------ Will-Return Attributes ----------------------------
 
 // Helper function that checks whether a function has any cycle.
@@ -5473,6 +5532,9 @@
   // Every function might be "will-return".
   getOrCreateAAFor<AAWillReturn>(FPos);
 
+  // Every function might be "undefined-behavior"
+  getOrCreateAAFor<AAUndefinedBehavior>(FPos);
+
   // Every function can be nounwind.
   getOrCreateAAFor<AANoUnwind>(FPos);
 
@@ -5776,6 +5838,7 @@
 const char AANonNull::ID = 0;
 const char AANoRecurse::ID = 0;
 const char AAWillReturn::ID = 0;
+const char AAUndefinedBehavior::ID = 0;
 const char AANoAlias::ID = 0;
 const char AAReachability::ID = 0;
 const char AANoReturn::ID = 0;
@@ -5883,6 +5946,7 @@
 CREATE_FUNCTION_ABSTRACT_ATTRIBUTE_FOR_POSITION(AANoSync)
 CREATE_FUNCTION_ABSTRACT_ATTRIBUTE_FOR_POSITION(AANoRecurse)
 CREATE_FUNCTION_ABSTRACT_ATTRIBUTE_FOR_POSITION(AAWillReturn)
+CREATE_FUNCTION_ABSTRACT_ATTRIBUTE_FOR_POSITION(AAUndefinedBehavior)
 CREATE_FUNCTION_ABSTRACT_ATTRIBUTE_FOR_POSITION(AANoReturn)
 CREATE_FUNCTION_ABSTRACT_ATTRIBUTE_FOR_POSITION(AAReturnedValues)