diff --git a/llvm/include/llvm/CodeGen/MIRYamlMapping.h b/llvm/include/llvm/CodeGen/MIRYamlMapping.h
--- a/llvm/include/llvm/CodeGen/MIRYamlMapping.h
+++ b/llvm/include/llvm/CodeGen/MIRYamlMapping.h
@@ -142,6 +142,23 @@
   }
 };
 
+template <> struct ScalarTraits<MaybeAlign> {
+  static void output(const MaybeAlign &Alignment, void *,
+                     llvm::raw_ostream &out) {
+    out << uint64_t(Alignment ? Alignment->value() : 0U);
+  }
+  static StringRef input(StringRef Scalar, void *, MaybeAlign &Alignment) {
+    unsigned long long n;
+    if (getAsUnsignedInteger(Scalar, 10, n))
+      return "invalid number";
+    if (n > 0 && !isPowerOf2_64(n))
+      return "must be 0 or a power of two";
+    Alignment = MaybeAlign(n);
+    return StringRef();
+  }
+  static QuotingType mustQuote(StringRef) { return QuotingType::None; }
+};
+
 } // end namespace yaml
 } // end namespace llvm
 
@@ -212,7 +229,7 @@
   ObjectType Type = DefaultType;
   int64_t Offset = 0;
   uint64_t Size = 0;
-  unsigned Alignment = 0;
+  MaybeAlign Alignment = None;
   TargetStackID::Value StackID;
   StringValue CalleeSavedRegister;
   bool CalleeSavedRestored = true;
@@ -252,7 +269,7 @@
     YamlIO.mapOptional("offset", Object.Offset, (int64_t)0);
     if (Object.Type != MachineStackObject::VariableSized)
       YamlIO.mapRequired("size", Object.Size);
-    YamlIO.mapOptional("alignment", Object.Alignment, (unsigned)0);
+    YamlIO.mapOptional("alignment", Object.Alignment, None);
     YamlIO.mapOptional("stack-id", Object.StackID, TargetStackID::Default);
     YamlIO.mapOptional("callee-saved-register", Object.CalleeSavedRegister,
                        StringValue()); // Don't print it out when it's empty.
@@ -278,7 +295,7 @@
   ObjectType Type = DefaultType;
   int64_t Offset = 0;
   uint64_t Size = 0;
-  unsigned Alignment = 0;
+  MaybeAlign Alignment = None;
   TargetStackID::Value StackID;
   bool IsImmutable = false;
   bool IsAliased = false;
@@ -327,7 +344,7 @@
         FixedMachineStackObject::DefaultType); // Don't print the default type.
     YamlIO.mapOptional("offset", Object.Offset, (int64_t)0);
     YamlIO.mapOptional("size", Object.Size, (uint64_t)0);
-    YamlIO.mapOptional("alignment", Object.Alignment, (unsigned)0);
+    YamlIO.mapOptional("alignment", Object.Alignment, None);
     YamlIO.mapOptional("stack-id", Object.StackID, TargetStackID::Default);
     if (Object.Type != FixedMachineStackObject::SpillSlot) {
       YamlIO.mapOptional("isImmutable", Object.IsImmutable, false);
@@ -411,7 +428,7 @@
 struct MachineConstantPoolValue {
   UnsignedValue ID;
   StringValue Value;
-  unsigned Alignment = 0;
+  MaybeAlign Alignment = None;
   bool IsTargetSpecific = false;
 
   bool operator==(const MachineConstantPoolValue &Other) const {
@@ -425,7 +442,7 @@
   static void mapping(IO &YamlIO, MachineConstantPoolValue &Constant) {
     YamlIO.mapRequired("id", Constant.ID);
     YamlIO.mapOptional("value", Constant.Value, StringValue());
-    YamlIO.mapOptional("alignment", Constant.Alignment, (unsigned)0);
+    YamlIO.mapOptional("alignment", Constant.Alignment, None);
     YamlIO.mapOptional("isTargetSpecific", Constant.IsTargetSpecific, false);
   }
 };
@@ -571,7 +588,7 @@
 
 struct MachineFunction {
   StringRef Name;
-  unsigned Alignment = 0;
+  MaybeAlign Alignment = None;
   bool ExposesReturnsTwice = false;
   // GISel MachineFunctionProperties.
   bool Legalized = false;
@@ -599,7 +616,7 @@
 template <> struct MappingTraits<MachineFunction> {
   static void mapping(IO &YamlIO, MachineFunction &MF) {
     YamlIO.mapRequired("name", MF.Name);
-    YamlIO.mapOptional("alignment", MF.Alignment, (unsigned)0);
+    YamlIO.mapOptional("alignment", MF.Alignment, None);
     YamlIO.mapOptional("exposesReturnsTwice", MF.ExposesReturnsTwice, false);
     YamlIO.mapOptional("legalized", MF.Legalized, false);
     YamlIO.mapOptional("regBankSelected", MF.RegBankSelected, false);
diff --git a/llvm/lib/CodeGen/MIRParser/MIRParser.cpp b/llvm/lib/CodeGen/MIRParser/MIRParser.cpp
--- a/llvm/lib/CodeGen/MIRParser/MIRParser.cpp
+++ b/llvm/lib/CodeGen/MIRParser/MIRParser.cpp
@@ -401,8 +401,7 @@
     Target.reset(new PerTargetMIParsingState(MF.getSubtarget()));
   }
 
-  if (YamlMF.Alignment)
-    MF.setAlignment(Align(YamlMF.Alignment));
+  MF.setAlignment(YamlMF.Alignment.valueOrOne());
   MF.setExposesReturnsTwice(YamlMF.ExposesReturnsTwice);
   MF.setHasWinCFI(YamlMF.HasWinCFI);
 
@@ -691,7 +690,7 @@
       return error(Object.ID.SourceRange.Start,
                    Twine("StackID is not supported by target"));
     MFI.setStackID(ObjectIdx, Object.StackID);
-    MFI.setObjectAlignment(ObjectIdx, Object.Alignment);
+    MFI.setObjectAlignment(ObjectIdx, Object.Alignment.valueOrOne());
     if (!PFS.FixedStackObjectSlots.insert(std::make_pair(Object.ID.Value,
                                                          ObjectIdx))
              .second)
@@ -723,10 +722,11 @@
       return error(Object.ID.SourceRange.Start,
                    Twine("StackID is not supported by target"));
     if (Object.Type == yaml::MachineStackObject::VariableSized)
-      ObjectIdx = MFI.CreateVariableSizedObject(Object.Alignment, Alloca);
+      ObjectIdx =
+          MFI.CreateVariableSizedObject(Object.Alignment.valueOrOne(), Alloca);
     else
       ObjectIdx = MFI.CreateStackObject(
-          Object.Size, Object.Alignment,
+          Object.Size, Object.Alignment.valueOrOne(),
           Object.Type == yaml::MachineStackObject::SpillSlot, Alloca,
           Object.StackID);
     MFI.setObjectOffset(ObjectIdx, Object.Offset);
@@ -838,11 +838,11 @@
         parseConstantValue(YamlConstant.Value.Value, Error, M));
     if (!Value)
       return error(Error, YamlConstant.Value.SourceRange);
-    unsigned Alignment =
-        YamlConstant.Alignment
-            ? YamlConstant.Alignment
-            : M.getDataLayout().getPrefTypeAlignment(Value->getType());
-    unsigned Index = ConstantPool.getConstantPoolIndex(Value, Alignment);
+    const Align PrefTypeAlign =
+        M.getDataLayout().getPrefTypeAlign(Value->getType());
+    const Align Alignment = YamlConstant.Alignment.getValueOr(PrefTypeAlign);
+    unsigned Index =
+        ConstantPool.getConstantPoolIndex(Value, Alignment.value());
     if (!ConstantPoolSlots.insert(std::make_pair(YamlConstant.ID.Value, Index))
              .second)
       return error(YamlConstant.ID.SourceRange.Start,
diff --git a/llvm/lib/CodeGen/MIRPrinter.cpp b/llvm/lib/CodeGen/MIRPrinter.cpp
--- a/llvm/lib/CodeGen/MIRPrinter.cpp
+++ b/llvm/lib/CodeGen/MIRPrinter.cpp
@@ -198,7 +198,7 @@
 
   yaml::MachineFunction YamlMF;
   YamlMF.Name = MF.getName();
-  YamlMF.Alignment = MF.getAlignment().value();
+  YamlMF.Alignment = MF.getAlignment();
   YamlMF.ExposesReturnsTwice = MF.exposesReturnsTwice();
   YamlMF.HasWinCFI = MF.hasWinCFI();
 
@@ -373,7 +373,7 @@
                           : yaml::FixedMachineStackObject::DefaultType;
     YamlObject.Offset = MFI.getObjectOffset(I);
     YamlObject.Size = MFI.getObjectSize(I);
-    YamlObject.Alignment = MFI.getObjectAlignment(I);
+    YamlObject.Alignment = MFI.getObjectAlign(I);
     YamlObject.StackID = (TargetStackID::Value)MFI.getStackID(I);
     YamlObject.IsImmutable = MFI.isImmutableObjectIndex(I);
     YamlObject.IsAliased = MFI.isAliasedObjectIndex(I);
@@ -400,7 +400,7 @@
                                 : yaml::MachineStackObject::DefaultType;
     YamlObject.Offset = MFI.getObjectOffset(I);
     YamlObject.Size = MFI.getObjectSize(I);
-    YamlObject.Alignment = MFI.getObjectAlignment(I);
+    YamlObject.Alignment = MFI.getObjectAlign(I);
     YamlObject.StackID = (TargetStackID::Value)MFI.getStackID(I);
 
     YMF.StackObjects.push_back(YamlObject);
@@ -514,7 +514,7 @@
     yaml::MachineConstantPoolValue YamlConstant;
     YamlConstant.ID = ID++;
     YamlConstant.Value = StrOS.str();
-    YamlConstant.Alignment = Constant.getAlignment();
+    YamlConstant.Alignment = MaybeAlign(Constant.getAlignment());
     YamlConstant.IsTargetSpecific = Constant.isMachineConstantPoolEntry();
 
     MF.Constants.push_back(YamlConstant);