Index: include/llvm/CodeGen/MIRYamlMapping.h
===================================================================
--- include/llvm/CodeGen/MIRYamlMapping.h
+++ include/llvm/CodeGen/MIRYamlMapping.h
@@ -344,8 +344,7 @@
   bool AdjustsStack = false;
   bool HasCalls = false;
   StringValue StackProtector;
-  // TODO: Serialize FunctionContextIdx
-  unsigned MaxCallFrameSize = 0;
+  unsigned MaxCallFrameSize = ~0u; ///< ~0u means: not computed yet.
   bool HasOpaqueSPAdjustment = false;
   bool HasVAStart = false;
   bool HasMustTailInVarArgFunc = false;
@@ -366,7 +365,7 @@
     YamlIO.mapOptional("hasCalls", MFI.HasCalls);
     YamlIO.mapOptional("stackProtector", MFI.StackProtector,
                        StringValue()); // Don't print it out when it's empty.
-    YamlIO.mapOptional("maxCallFrameSize", MFI.MaxCallFrameSize);
+    YamlIO.mapOptional("maxCallFrameSize", MFI.MaxCallFrameSize, ~0u);
     YamlIO.mapOptional("hasOpaqueSPAdjustment", MFI.HasOpaqueSPAdjustment);
     YamlIO.mapOptional("hasVAStart", MFI.HasVAStart);
     YamlIO.mapOptional("hasMustTailInVarArgFunc", MFI.HasMustTailInVarArgFunc);
Index: include/llvm/CodeGen/MachineFrameInfo.h
===================================================================
--- include/llvm/CodeGen/MachineFrameInfo.h
+++ include/llvm/CodeGen/MachineFrameInfo.h
@@ -220,7 +220,7 @@
   /// setup/destroy pseudo instructions (as defined in the TargetFrameInfo
   /// class).  This information is important for frame pointer elimination.
   /// It is only valid during and after prolog/epilog code insertion.
-  unsigned MaxCallFrameSize = 0;
+  unsigned MaxCallFrameSize = ~0u;
 
   /// The prolog/epilog code inserter fills in this vector with each
   /// callee saved register saved in the frame.  Beyond its use by the prolog/
@@ -525,7 +525,14 @@
   /// CallFrameSetup/Destroy pseudo instructions are used by the target, and
   /// then only during or after prolog/epilog code insertion.
   ///
-  unsigned getMaxCallFrameSize() const { return MaxCallFrameSize; }
+  unsigned getMaxCallFrameSize() const {
+    // TODO: Enable this assert when targets are fixed.
+    //assert(isMaxCallFrameSizeComputed() && "MaxCallFrameSize not computed yet");
+    return MaxCallFrameSize;
+  }
+  bool isMaxCallFrameSizeComputed() const {
+    return MaxCallFrameSize != ~0u;
+  }
   void setMaxCallFrameSize(unsigned S) { MaxCallFrameSize = S; }
 
   /// Create a new object at a fixed location on the stack.
Index: lib/CodeGen/MIRParser/MIRParser.cpp
===================================================================
--- lib/CodeGen/MIRParser/MIRParser.cpp
+++ lib/CodeGen/MIRParser/MIRParser.cpp
@@ -541,7 +541,8 @@
     MFI.ensureMaxAlignment(YamlMFI.MaxAlignment);
   MFI.setAdjustsStack(YamlMFI.AdjustsStack);
   MFI.setHasCalls(YamlMFI.HasCalls);
-  MFI.setMaxCallFrameSize(YamlMFI.MaxCallFrameSize);
+  if (YamlMFI.MaxCallFrameSize != ~0u)
+    MFI.setMaxCallFrameSize(YamlMFI.MaxCallFrameSize);
   MFI.setHasOpaqueSPAdjustment(YamlMFI.HasOpaqueSPAdjustment);
   MFI.setHasVAStart(YamlMFI.HasVAStart);
   MFI.setHasMustTailInVarArgFunc(YamlMFI.HasMustTailInVarArgFunc);
Index: lib/CodeGen/MIRPrinter.cpp
===================================================================
--- lib/CodeGen/MIRPrinter.cpp
+++ lib/CodeGen/MIRPrinter.cpp
@@ -286,7 +286,8 @@
   YamlMFI.MaxAlignment = MFI.getMaxAlignment();
   YamlMFI.AdjustsStack = MFI.adjustsStack();
   YamlMFI.HasCalls = MFI.hasCalls();
-  YamlMFI.MaxCallFrameSize = MFI.getMaxCallFrameSize();
+  YamlMFI.MaxCallFrameSize = MFI.isMaxCallFrameSizeComputed()
+    ? MFI.getMaxCallFrameSize() : ~0u;
   YamlMFI.HasOpaqueSPAdjustment = MFI.hasOpaqueSPAdjustment();
   YamlMFI.HasVAStart = MFI.hasVAStart();
   YamlMFI.HasMustTailInVarArgFunc = MFI.hasMustTailInVarArgFunc();