Index: llvm/trunk/include/llvm/CodeGen/MIRYamlMapping.h
===================================================================
--- llvm/trunk/include/llvm/CodeGen/MIRYamlMapping.h
+++ llvm/trunk/include/llvm/CodeGen/MIRYamlMapping.h
@@ -72,6 +72,9 @@
 
 struct BlockStringValue {
   StringValue Value;
+  bool operator==(const BlockStringValue &Other) const {
+    return Value == Other.Value;
+  }
 };
 
 template <> struct BlockScalarTraits<BlockStringValue> {
@@ -146,6 +149,10 @@
   StringValue Class;
   StringValue PreferredRegister;
   // TODO: Serialize the target specific register hints.
+  bool operator==(const VirtualRegisterDefinition &Other) const {
+    return ID == Other.ID && Class == Other.Class &&
+           PreferredRegister == Other.PreferredRegister;
+  }
 };
 
 template <> struct MappingTraits<VirtualRegisterDefinition> {
@@ -162,6 +169,10 @@
 struct MachineFunctionLiveIn {
   StringValue Register;
   StringValue VirtualRegister;
+  bool operator==(const MachineFunctionLiveIn &Other) const {
+    return Register == Other.Register &&
+           VirtualRegister == Other.VirtualRegister;
+  }
 };
 
 template <> struct MappingTraits<MachineFunctionLiveIn> {
@@ -196,6 +207,14 @@
   StringValue DebugVar;
   StringValue DebugExpr;
   StringValue DebugLoc;
+  bool operator==(const MachineStackObject &Other) const {
+    return ID == Other.ID && Name == Other.Name && Type == Other.Type &&
+           Offset == Other.Offset && Size == Other.Size &&
+           Alignment == Other.Alignment &&
+           CalleeSavedRegister == Other.CalleeSavedRegister &&
+           LocalOffset == Other.LocalOffset && DebugVar == Other.DebugVar &&
+           DebugExpr == Other.DebugExpr && DebugLoc == Other.DebugLoc;
+  }
 };
 
 template <> struct ScalarEnumerationTraits<MachineStackObject::ObjectType> {
@@ -214,13 +233,13 @@
     YamlIO.mapOptional(
         "type", Object.Type,
         MachineStackObject::DefaultType); // Don't print the default type.
-    YamlIO.mapOptional("offset", Object.Offset);
+    YamlIO.mapOptional("offset", Object.Offset, 0LL);
     if (Object.Type != MachineStackObject::VariableSized)
       YamlIO.mapRequired("size", Object.Size);
-    YamlIO.mapOptional("alignment", Object.Alignment);
+    YamlIO.mapOptional("alignment", Object.Alignment, 0U);
     YamlIO.mapOptional("callee-saved-register", Object.CalleeSavedRegister,
                        StringValue()); // Don't print it out when it's empty.
-    YamlIO.mapOptional("local-offset", Object.LocalOffset);
+    YamlIO.mapOptional("local-offset", Object.LocalOffset, Optional<int64_t>());
     YamlIO.mapOptional("di-variable", Object.DebugVar,
                        StringValue()); // Don't print it out when it's empty.
     YamlIO.mapOptional("di-expression", Object.DebugExpr,
@@ -244,6 +263,12 @@
   bool IsImmutable = false;
   bool IsAliased = false;
   StringValue CalleeSavedRegister;
+  bool operator==(const FixedMachineStackObject &Other) const {
+    return ID == Other.ID && Type == Other.Type && Offset == Other.Offset &&
+           Size == Other.Size && Alignment == Other.Alignment &&
+           IsImmutable == Other.IsImmutable && IsAliased == Other.IsAliased &&
+           CalleeSavedRegister == Other.CalleeSavedRegister;
+  }
 };
 
 template <>
@@ -261,12 +286,12 @@
     YamlIO.mapOptional(
         "type", Object.Type,
         FixedMachineStackObject::DefaultType); // Don't print the default type.
-    YamlIO.mapOptional("offset", Object.Offset);
-    YamlIO.mapOptional("size", Object.Size);
-    YamlIO.mapOptional("alignment", Object.Alignment);
+    YamlIO.mapOptional("offset", Object.Offset, 0LL);
+    YamlIO.mapOptional("size", Object.Size, 0ULL);
+    YamlIO.mapOptional("alignment", Object.Alignment, 0U);
     if (Object.Type != FixedMachineStackObject::SpillSlot) {
-      YamlIO.mapOptional("isImmutable", Object.IsImmutable);
-      YamlIO.mapOptional("isAliased", Object.IsAliased);
+      YamlIO.mapOptional("isImmutable", Object.IsImmutable, false);
+      YamlIO.mapOptional("isAliased", Object.IsAliased, false);
     }
     YamlIO.mapOptional("callee-saved-register", Object.CalleeSavedRegister,
                        StringValue()); // Don't print it out when it's empty.
@@ -279,13 +304,17 @@
   UnsignedValue ID;
   StringValue Value;
   unsigned Alignment = 0;
+  bool operator==(const MachineConstantPoolValue &Other) const {
+    return ID == Other.ID && Value == Other.Value &&
+           Alignment == Other.Alignment;
+  }
 };
 
 template <> struct MappingTraits<MachineConstantPoolValue> {
   static void mapping(IO &YamlIO, MachineConstantPoolValue &Constant) {
     YamlIO.mapRequired("id", Constant.ID);
-    YamlIO.mapOptional("value", Constant.Value);
-    YamlIO.mapOptional("alignment", Constant.Alignment);
+    YamlIO.mapOptional("value", Constant.Value, StringValue());
+    YamlIO.mapOptional("alignment", Constant.Alignment, 0U);
   }
 };
 
@@ -293,16 +322,22 @@
   struct Entry {
     UnsignedValue ID;
     std::vector<FlowStringValue> Blocks;
+    bool operator==(const Entry &Other) const {
+      return ID == Other.ID && Blocks == Other.Blocks;
+    }
   };
 
   MachineJumpTableInfo::JTEntryKind Kind = MachineJumpTableInfo::EK_Custom32;
   std::vector<Entry> Entries;
+  bool operator==(const MachineJumpTable &Other) const {
+    return Kind == Other.Kind && Entries == Other.Entries;
+  }
 };
 
 template <> struct MappingTraits<MachineJumpTable::Entry> {
   static void mapping(IO &YamlIO, MachineJumpTable::Entry &Entry) {
     YamlIO.mapRequired("id", Entry.ID);
-    YamlIO.mapOptional("blocks", Entry.Blocks);
+    YamlIO.mapOptional("blocks", Entry.Blocks, std::vector<FlowStringValue>());
   }
 };
 
@@ -322,7 +357,8 @@
 template <> struct MappingTraits<MachineJumpTable> {
   static void mapping(IO &YamlIO, MachineJumpTable &JT) {
     YamlIO.mapRequired("kind", JT.Kind);
-    YamlIO.mapOptional("entries", JT.Entries);
+    YamlIO.mapOptional("entries", JT.Entries,
+                       std::vector<MachineJumpTable::Entry>());
   }
 };
 
@@ -351,25 +387,43 @@
   bool HasMustTailInVarArgFunc = false;
   StringValue SavePoint;
   StringValue RestorePoint;
+  bool operator==(const MachineFrameInfo &Other) const {
+    return IsFrameAddressTaken == Other.IsFrameAddressTaken &&
+           IsReturnAddressTaken == Other.IsReturnAddressTaken &&
+           HasStackMap == Other.HasStackMap &&
+           HasPatchPoint == Other.HasPatchPoint &&
+           StackSize == Other.StackSize &&
+           OffsetAdjustment == Other.OffsetAdjustment &&
+           MaxAlignment == Other.MaxAlignment &&
+           AdjustsStack == Other.AdjustsStack && HasCalls == Other.HasCalls &&
+           StackProtector == Other.StackProtector &&
+           MaxCallFrameSize == Other.MaxCallFrameSize &&
+           HasOpaqueSPAdjustment == Other.HasOpaqueSPAdjustment &&
+           HasVAStart == Other.HasVAStart &&
+           HasMustTailInVarArgFunc == Other.HasMustTailInVarArgFunc &&
+           SavePoint == Other.SavePoint && RestorePoint == Other.RestorePoint;
+  }
 };
 
 template <> struct MappingTraits<MachineFrameInfo> {
   static void mapping(IO &YamlIO, MachineFrameInfo &MFI) {
-    YamlIO.mapOptional("isFrameAddressTaken", MFI.IsFrameAddressTaken);
-    YamlIO.mapOptional("isReturnAddressTaken", MFI.IsReturnAddressTaken);
-    YamlIO.mapOptional("hasStackMap", MFI.HasStackMap);
-    YamlIO.mapOptional("hasPatchPoint", MFI.HasPatchPoint);
-    YamlIO.mapOptional("stackSize", MFI.StackSize);
-    YamlIO.mapOptional("offsetAdjustment", MFI.OffsetAdjustment);
-    YamlIO.mapOptional("maxAlignment", MFI.MaxAlignment);
-    YamlIO.mapOptional("adjustsStack", MFI.AdjustsStack);
-    YamlIO.mapOptional("hasCalls", MFI.HasCalls);
+    YamlIO.mapOptional("isFrameAddressTaken", MFI.IsFrameAddressTaken, false);
+    YamlIO.mapOptional("isReturnAddressTaken", MFI.IsReturnAddressTaken, false);
+    YamlIO.mapOptional("hasStackMap", MFI.HasStackMap, false);
+    YamlIO.mapOptional("hasPatchPoint", MFI.HasPatchPoint, false);
+    YamlIO.mapOptional("stackSize", MFI.StackSize, 0ULL);
+    YamlIO.mapOptional("offsetAdjustment", MFI.OffsetAdjustment, 0);
+    YamlIO.mapOptional("maxAlignment", MFI.MaxAlignment, 0U);
+    YamlIO.mapOptional("adjustsStack", MFI.AdjustsStack, false);
+    YamlIO.mapOptional("hasCalls", MFI.HasCalls, false);
     YamlIO.mapOptional("stackProtector", MFI.StackProtector,
                        StringValue()); // Don't print it out when it's empty.
     YamlIO.mapOptional("maxCallFrameSize", MFI.MaxCallFrameSize, ~0u);
-    YamlIO.mapOptional("hasOpaqueSPAdjustment", MFI.HasOpaqueSPAdjustment);
-    YamlIO.mapOptional("hasVAStart", MFI.HasVAStart);
-    YamlIO.mapOptional("hasMustTailInVarArgFunc", MFI.HasMustTailInVarArgFunc);
+    YamlIO.mapOptional("hasOpaqueSPAdjustment", MFI.HasOpaqueSPAdjustment,
+                       false);
+    YamlIO.mapOptional("hasVAStart", MFI.HasVAStart, false);
+    YamlIO.mapOptional("hasMustTailInVarArgFunc", MFI.HasMustTailInVarArgFunc,
+                       false);
     YamlIO.mapOptional("savePoint", MFI.SavePoint,
                        StringValue()); // Don't print it out when it's empty.
     YamlIO.mapOptional("restorePoint", MFI.RestorePoint,
@@ -404,23 +458,29 @@
 template <> struct MappingTraits<MachineFunction> {
   static void mapping(IO &YamlIO, MachineFunction &MF) {
     YamlIO.mapRequired("name", MF.Name);
-    YamlIO.mapOptional("alignment", MF.Alignment);
-    YamlIO.mapOptional("exposesReturnsTwice", MF.ExposesReturnsTwice);
+    YamlIO.mapOptional("alignment", MF.Alignment, 0U);
+    YamlIO.mapOptional("exposesReturnsTwice", MF.ExposesReturnsTwice, false);
     YamlIO.mapOptional("noVRegs", MF.NoVRegs);
-    YamlIO.mapOptional("legalized", MF.Legalized);
-    YamlIO.mapOptional("regBankSelected", MF.RegBankSelected);
-    YamlIO.mapOptional("selected", MF.Selected);
-    YamlIO.mapOptional("tracksRegLiveness", MF.TracksRegLiveness);
-    YamlIO.mapOptional("registers", MF.VirtualRegisters);
-    YamlIO.mapOptional("liveins", MF.LiveIns);
-    YamlIO.mapOptional("calleeSavedRegisters", MF.CalleeSavedRegisters);
-    YamlIO.mapOptional("frameInfo", MF.FrameInfo);
-    YamlIO.mapOptional("fixedStack", MF.FixedStackObjects);
-    YamlIO.mapOptional("stack", MF.StackObjects);
-    YamlIO.mapOptional("constants", MF.Constants);
+    YamlIO.mapOptional("legalized", MF.Legalized, false);
+    YamlIO.mapOptional("regBankSelected", MF.RegBankSelected, false);
+    YamlIO.mapOptional("selected", MF.Selected, false);
+    YamlIO.mapOptional("tracksRegLiveness", MF.TracksRegLiveness, false);
+    YamlIO.mapOptional("registers", MF.VirtualRegisters,
+                       std::vector<VirtualRegisterDefinition>());
+    YamlIO.mapOptional("liveins", MF.LiveIns,
+                       std::vector<MachineFunctionLiveIn>());
+    YamlIO.mapOptional("calleeSavedRegisters", MF.CalleeSavedRegisters,
+                       Optional<std::vector<FlowStringValue>>());
+    YamlIO.mapOptional("frameInfo", MF.FrameInfo, MachineFrameInfo());
+    YamlIO.mapOptional("fixedStack", MF.FixedStackObjects,
+                       std::vector<FixedMachineStackObject>());
+    YamlIO.mapOptional("stack", MF.StackObjects,
+                       std::vector<MachineStackObject>());
+    YamlIO.mapOptional("constants", MF.Constants,
+                       std::vector<MachineConstantPoolValue>());
     if (!YamlIO.outputting() || !MF.JumpTableInfo.Entries.empty())
-      YamlIO.mapOptional("jumpTable", MF.JumpTableInfo);
-    YamlIO.mapOptional("body", MF.Body);
+      YamlIO.mapOptional("jumpTable", MF.JumpTableInfo, MachineJumpTable());
+    YamlIO.mapOptional("body", MF.Body, BlockStringValue());
   }
 };
 
Index: llvm/trunk/lib/CodeGen/MIRPrinter.cpp
===================================================================
--- llvm/trunk/lib/CodeGen/MIRPrinter.cpp
+++ llvm/trunk/lib/CodeGen/MIRPrinter.cpp
@@ -212,6 +212,8 @@
   }
   StrOS.flush();
   yaml::Output Out(OS);
+  if (!SimplifyMIR)
+      Out.setWriteDefaultValues(true);
   Out << YamlMF;
 }