Index: include/llvm/CodeGen/MIRYamlMapping.h
===================================================================
--- include/llvm/CodeGen/MIRYamlMapping.h
+++ include/llvm/CodeGen/MIRYamlMapping.h
@@ -310,6 +310,7 @@
   UnsignedValue ID;
   StringValue Value;
   unsigned Alignment = 0;
+  bool IsTargetSpecific = false;
   bool operator==(const MachineConstantPoolValue &Other) const {
     return ID == Other.ID && Value == Other.Value &&
            Alignment == Other.Alignment;
@@ -321,6 +322,7 @@
     YamlIO.mapRequired("id", Constant.ID);
     YamlIO.mapOptional("value", Constant.Value, StringValue());
     YamlIO.mapOptional("alignment", Constant.Alignment, (unsigned)0);
+    YamlIO.mapOptional("isTargetSpecific", Constant.IsTargetSpecific);
   }
 };
 
Index: lib/CodeGen/MIRParser/MIRParser.cpp
===================================================================
--- lib/CodeGen/MIRParser/MIRParser.cpp
+++ lib/CodeGen/MIRParser/MIRParser.cpp
@@ -719,6 +719,10 @@
   const auto &M = *MF.getFunction()->getParent();
   SMDiagnostic Error;
   for (const auto &YamlConstant : YamlMF.Constants) {
+    if (YamlConstant.IsTargetSpecific)
+      // FIXME: Support target-specific constant pools
+      return error(YamlConstant.Value.SourceRange.Start,
+                   "Can't parse target-specific constant pool entries yet");
     const Constant *Value = dyn_cast_or_null<Constant>(
         parseConstantValue(YamlConstant.Value.Value, Error, M));
     if (!Value)
Index: lib/CodeGen/MIRPrinter.cpp
===================================================================
--- lib/CodeGen/MIRPrinter.cpp
+++ lib/CodeGen/MIRPrinter.cpp
@@ -458,17 +458,20 @@
                          const MachineConstantPool &ConstantPool) {
   unsigned ID = 0;
   for (const MachineConstantPoolEntry &Constant : ConstantPool.getConstants()) {
-    // TODO: Serialize target specific constant pool entries.
-    if (Constant.isMachineConstantPoolEntry())
-      llvm_unreachable("Can't print target specific constant pool entries yet");
-
-    yaml::MachineConstantPoolValue YamlConstant;
     std::string Str;
     raw_string_ostream StrOS(Str);
-    Constant.Val.ConstVal->printAsOperand(StrOS);
+    if (Constant.isMachineConstantPoolEntry()) {
+      Constant.Val.MachineCPVal->print(StrOS);
+    } else {
+      Constant.Val.ConstVal->printAsOperand(StrOS);
+    }
+
+    yaml::MachineConstantPoolValue YamlConstant;
     YamlConstant.ID = ID++;
     YamlConstant.Value = StrOS.str();
     YamlConstant.Alignment = Constant.getAlignment();
+    YamlConstant.IsTargetSpecific = Constant.isMachineConstantPoolEntry();
+
     MF.Constants.push_back(YamlConstant);
   }
 }