diff --git a/llvm/utils/TableGen/CodeGenTarget.h b/llvm/utils/TableGen/CodeGenTarget.h
--- a/llvm/utils/TableGen/CodeGenTarget.h
+++ b/llvm/utils/TableGen/CodeGenTarget.h
@@ -60,6 +60,7 @@
 
   mutable std::unique_ptr<CodeGenSchedModels> SchedModels;
 
+  mutable StringRef InstNamespace;
   mutable std::vector<const CodeGenInstruction*> InstrsByEnum;
   mutable unsigned NumPseudoInstructions = 0;
 public:
diff --git a/llvm/utils/TableGen/CodeGenTarget.cpp b/llvm/utils/TableGen/CodeGenTarget.cpp
--- a/llvm/utils/TableGen/CodeGenTarget.cpp
+++ b/llvm/utils/TableGen/CodeGenTarget.cpp
@@ -264,15 +264,20 @@
   return TargetRec->getName();
 }
 
+/// getInstNamespace - Find and return the target machine's instruction
+/// namespace. The namespace is cached because it is requested multiple times.
 StringRef CodeGenTarget::getInstNamespace() const {
-  for (const CodeGenInstruction *Inst : getInstructionsByEnumValue()) {
-    // Make sure not to pick up "TargetOpcode" by accidentally getting
-    // the namespace off the PHI instruction or something.
-    if (Inst->Namespace != "TargetOpcode")
-      return Inst->Namespace;
+  if (InstNamespace.empty()) {
+    for (const CodeGenInstruction *Inst : getInstructionsByEnumValue()) {
+      // We are not interested in the "TargetOpcode" namespace.
+      if (Inst->Namespace != "TargetOpcode") {
+        InstNamespace = Inst->Namespace;
+        break;
+      }
+    }
   }
 
-  return "";
+  return InstNamespace;
 }
 
 StringRef CodeGenTarget::getRegNamespace() const {