diff --git a/llvm/include/llvm/ADT/DenseMap.h b/llvm/include/llvm/ADT/DenseMap.h
--- a/llvm/include/llvm/ADT/DenseMap.h
+++ b/llvm/include/llvm/ADT/DenseMap.h
@@ -16,8 +16,10 @@
 
 #include "llvm/ADT/DenseMapInfo.h"
 #include "llvm/ADT/EpochTracker.h"
+#include "llvm/ADT/Twine.h"
 #include "llvm/Support/AlignOf.h"
 #include "llvm/Support/Compiler.h"
+#include "llvm/Support/Debug.h"
 #include "llvm/Support/MathExtras.h"
 #include "llvm/Support/MemAlloc.h"
 #include "llvm/Support/ReverseIteration.h"
@@ -201,6 +203,16 @@
     return ValueT();
   }
 
+  /// lookupOrTrap - Return the entry for the specified key, or abort with given
+  /// message if no such entry exists.
+  ValueT lookupOrTrap(const_arg_type_t<KeyT> Val, const Twine &Msg = "") const {
+    auto Iter = this->find(std::move(Val));
+    if (Iter != this->end())
+      return Iter->second;
+    dbgs() << "[DenseMap::lookupOrTrap] key not found; " << Msg << "\n";
+    std::abort();
+  }
+
   // Inserts key,value pair into the map if the key isn't already in the map.
   // If the key is already in the map, it returns false and doesn't update the
   // value.
diff --git a/llvm/unittests/ADT/DenseMapTest.cpp b/llvm/unittests/ADT/DenseMapTest.cpp
--- a/llvm/unittests/ADT/DenseMapTest.cpp
+++ b/llvm/unittests/ADT/DenseMapTest.cpp
@@ -125,6 +125,13 @@
   EXPECT_TRUE(this->Map.find(this->getKey()) == this->Map.end());
   EXPECT_EQ(typename TypeParam::mapped_type(),
             this->Map.lookup(this->getKey()));
+
+  // LookupOrTrap tests
+  EXPECT_DEATH({ this->Map.lookupOrTrap(this->getKey()); },
+               "\\[DenseMap::lookupOrTrap\\] key not found;");
+  EXPECT_DEATH(
+      { this->Map.lookupOrTrap(this->getKey(), "clarification message 1"); },
+      "\\[DenseMap::lookupOrTrap\\] key not found; clarification message 1");
 }
 
 // Constant map tests
@@ -156,6 +163,13 @@
   EXPECT_TRUE(this->Map.find(this->getKey()) == this->Map.begin());
   EXPECT_EQ(this->getValue(), this->Map.lookup(this->getKey()));
   EXPECT_EQ(this->getValue(), this->Map[this->getKey()]);
+
+  // LookupOrTrap tests
+  EXPECT_DEATH({ this->Map.lookupOrTrap(this->getKey(1)); },
+               "\\[DenseMap::lookupOrTrap\\] key not found;");
+  EXPECT_DEATH(
+      { this->Map.lookupOrTrap(this->getKey(1), "clarification message 2"); },
+      "\\[DenseMap::lookupOrTrap\\] key not found; clarification message 2");
 }
 
 // Test clear() method