Index: llvm/docs/TableGen/BackGuide.rst
===================================================================
--- llvm/docs/TableGen/BackGuide.rst
+++ llvm/docs/TableGen/BackGuide.rst
@@ -571,7 +571,7 @@
 
 * ``getAllDerivedDefinitionsTwo(``\ *classname1*\ ``,`` *classname2*\ ``)`` returns
   a vector of ``Record`` references for the concrete records that derive from
-  *both* of the given classes. [function to come]
+  *both* of the given classes.
 
 This statement obtains all the records that derive from the ``Attribute``
 class and iterates over them.
@@ -701,7 +701,7 @@
 defined through a sequence of multiclasses. Because of this, it can be
 difficult for backends to report clear error messages with accurate source
 file locations.  To make error reporting easier, five error reporting
-functions are provided, each with four overloads. [all combinations to come]
+functions are provided, each with four overloads.
 
 * ``PrintWarning`` prints a message tagged as a warning.
 
Index: llvm/include/llvm/TableGen/Record.h
===================================================================
--- llvm/include/llvm/TableGen/Record.h
+++ llvm/include/llvm/TableGen/Record.h
@@ -1788,6 +1788,11 @@
   /// class. The class must be defined.
   std::vector<Record *> getAllDerivedDefinitions(StringRef ClassName) const;
 
+  /// Get all the concrete records that inherit from both of the specified
+  /// classes. The classes must be defined.
+  std::vector<Record *> getAllDerivedDefinitionsTwo(StringRef ClassName1,
+                                                    StringRef ClassName2) const;
+
   void dump() const;
 };
 
Index: llvm/lib/TableGen/Record.cpp
===================================================================
--- llvm/lib/TableGen/Record.cpp
+++ llvm/lib/TableGen/Record.cpp
@@ -2474,7 +2474,7 @@
 RecordKeeper::getAllDerivedDefinitions(StringRef ClassName) const {
   Record *Class = getClass(ClassName);
   if (!Class)
-    PrintFatalError("ERROR: Couldn't find the `" + ClassName + "' class!\n");
+    PrintFatalError("The class '" + ClassName + "' is not defined\n");
 
   std::vector<Record*> Defs;
   for (const auto &D : getDefs())
@@ -2484,6 +2484,24 @@
   return Defs;
 }
 
+std::vector<Record *>
+RecordKeeper::getAllDerivedDefinitionsTwo(StringRef ClassName1,
+                                          StringRef ClassName2) const {
+  Record *Class1 = getClass(ClassName1);
+  Record *Class2 = getClass(ClassName2);
+  if (!Class1)
+    PrintFatalError("The class '" + ClassName1 + "' is not defined\n");
+  if (!Class2)
+    PrintFatalError("The class '" + ClassName2 + "' is not defined\n");
+
+  std::vector<Record*> Defs;
+  for (const auto &D : getDefs())
+    if (D.second->isSubClassOf(Class1) && D.second->isSubClassOf(Class2))
+      Defs.push_back(D.second.get());
+
+  return Defs;
+}
+
 Init *MapResolver::resolve(Init *VarName) {
   auto It = Map.find(VarName);
   if (It == Map.end())
Index: llvm/utils/TableGen/PseudoLoweringEmitter.cpp
===================================================================
--- llvm/utils/TableGen/PseudoLoweringEmitter.cpp
+++ llvm/utils/TableGen/PseudoLoweringEmitter.cpp
@@ -293,17 +293,9 @@
 }
 
 void PseudoLoweringEmitter::run(raw_ostream &o) {
-  Record *ExpansionClass = Records.getClass("PseudoInstExpansion");
-  Record *InstructionClass = Records.getClass("Instruction");
-  assert(ExpansionClass && "PseudoInstExpansion class definition missing!");
-  assert(InstructionClass && "Instruction class definition missing!");
-
-  std::vector<Record*> Insts;
-  for (const auto &D : Records.getDefs()) {
-    if (D.second->isSubClassOf(ExpansionClass) &&
-        D.second->isSubClassOf(InstructionClass))
-      Insts.push_back(D.second.get());
-  }
+
+  std::vector<Record *> Insts =
+      Records.getAllDerivedDefinitionsTwo("PseudoInstExpansion", "Instruction");
 
   // Process the pseudo expansion definitions, validating them as we do so.
   for (unsigned i = 0, e = Insts.size(); i != e; ++i)
Index: llvm/utils/TableGen/RISCVCompressInstEmitter.cpp
===================================================================
--- llvm/utils/TableGen/RISCVCompressInstEmitter.cpp
+++ llvm/utils/TableGen/RISCVCompressInstEmitter.cpp
@@ -884,13 +884,8 @@
 }
 
 void RISCVCompressInstEmitter::run(raw_ostream &o) {
-  Record *CompressClass = Records.getClass("CompressPat");
-  assert(CompressClass && "Compress class definition missing!");
-  std::vector<Record *> Insts;
-  for (const auto &D : Records.getDefs()) {
-    if (D.second->isSubClassOf(CompressClass))
-      Insts.push_back(D.second.get());
-  }
+  std::vector<Record *> Insts = 
+      Records.getAllDerivedDefinitions("CompressPat");
 
   // Process the CompressPat definitions, validating them as we do so.
   for (unsigned i = 0, e = Insts.size(); i != e; ++i)