Index: include/llvm/Target/TargetCallingConv.td
===================================================================
--- include/llvm/Target/TargetCallingConv.td
+++ include/llvm/Target/TargetCallingConv.td
@@ -147,6 +147,13 @@
 /// that the target supports.
 class CallingConv<list<CCAction> actions> {
   list<CCAction> Actions = actions;
+  bit Custom = 0;
+}
+
+/// CustomCallingConv - An instance of this is used to declare calling
+/// conventions that are implemented using a custom function of the same name.
+class CustomCallingConv : CallingConv<[]> {
+  let Custom = 1;
 }
 
 /// CalleeSavedRegs - A list of callee saved registers for a given calling
Index: lib/Target/Mips/MipsCallingConv.td
===================================================================
--- lib/Target/Mips/MipsCallingConv.td
+++ lib/Target/Mips/MipsCallingConv.td
@@ -66,6 +66,14 @@
   CCIfType<[f64], CCIfSubtargetNot<"isFP64bit()", CCAssignToReg<[D0, D1]>>>
 ]>;
 
+def CC_MipsO32_FP32 : CustomCallingConv;
+def CC_MipsO32_FP64 : CustomCallingConv;
+
+def CC_MipsO32_FP : CallingConv<[
+  CCIfSubtargetNot<"isFP64bit()", CCDelegateTo<CC_MipsO32_FP32>>,
+  CCIfSubtarget<"isFP64bit()", CCDelegateTo<CC_MipsO32_FP64>>
+]>;
+
 //===----------------------------------------------------------------------===//
 // Mips N32/64 Calling Convention
 //===----------------------------------------------------------------------===//
@@ -288,6 +296,22 @@
   CCDelegateTo<RetCC_MipsO32>
 ]>;
 
+def CC_Mips_FixedArg : CallingConv<[
+  CCIfCC<"CallingConv::Fast", CCDelegateTo<CC_Mips_FastCC>>,
+
+  // FIXME: There wasn't an EABI case in the original code and it seems unlikely
+  //        that it's the same as CC_MipsN
+  CCIfSubtarget<"isABI_O32()", CCDelegateTo<CC_MipsO32_FP>>,
+  CCDelegateTo<CC_MipsN>
+]>;
+
+def CC_Mips_VarArg : CallingConv<[
+  // FIXME: There wasn't an EABI case in the original code and it seems unlikely
+  //        that it's the same as CC_MipsN_VarArg
+  CCIfSubtarget<"isABI_O32()", CCDelegateTo<CC_MipsO32_FP>>,
+  CCDelegateTo<CC_MipsN_VarArg>
+]>;
+
 //===----------------------------------------------------------------------===//
 // Callee-saved register lists.
 //===----------------------------------------------------------------------===//
Index: lib/Target/Mips/MipsISelLowering.h
===================================================================
--- lib/Target/Mips/MipsISelLowering.h
+++ lib/Target/Mips/MipsISelLowering.h
@@ -396,9 +396,6 @@
       /// Return the function that analyzes fixed argument list functions.
       llvm::CCAssignFn *fixedArgFn() const;
 
-      /// Return the function that analyzes variable argument list functions.
-      llvm::CCAssignFn *varArgFn() const;
-
       const MCPhysReg *shadowRegs() const;
 
       void allocateRegs(ByValArgInfo &ByVal, unsigned ByValSize,
Index: lib/Target/Mips/MipsISelLowering.cpp
===================================================================
--- lib/Target/Mips/MipsISelLowering.cpp
+++ lib/Target/Mips/MipsISelLowering.cpp
@@ -3547,7 +3547,7 @@
          "CallingConv::Fast shouldn't be used for vararg functions.");
 
   unsigned NumOpnds = Args.size();
-  llvm::CCAssignFn *FixedFn = fixedArgFn(), *VarFn = varArgFn();
+  llvm::CCAssignFn *FixedFn = fixedArgFn();
 
   for (unsigned I = 0; I != NumOpnds; ++I) {
     MVT ArgVT = Args[I].VT;
@@ -3560,7 +3560,7 @@
     }
 
     if (IsVarArg && !Args[I].IsFixed)
-      R = VarFn(I, ArgVT, ArgVT, CCValAssign::Full, ArgFlags, CCInfo);
+      R = CC_Mips_VarArg(I, ArgVT, ArgVT, CCValAssign::Full, ArgFlags, CCInfo);
     else {
       MVT RegVT = getRegVT(ArgVT, FuncArgs[Args[I].OrigArgIndex].Ty, CallNode,
                            IsSoftFloat);
@@ -3643,20 +3643,11 @@
 }
 
 llvm::CCAssignFn *MipsTargetLowering::MipsCC::fixedArgFn() const {
-  if (CallConv == CallingConv::Fast)
-    return CC_Mips_FastCC;
-
-  if (SpecialCallingConv == Mips16RetHelperConv)
+  if (CallConv != CallingConv::Fast &&
+      SpecialCallingConv == Mips16RetHelperConv)
     return CC_Mips16RetHelper;
-  return Subtarget.isABI_O32()
-             ? (Subtarget.isFP64bit() ? CC_MipsO32_FP64 : CC_MipsO32_FP32)
-             : CC_MipsN;
-}
 
-llvm::CCAssignFn *MipsTargetLowering::MipsCC::varArgFn() const {
-  return Subtarget.isABI_O32()
-             ? (Subtarget.isFP64bit() ? CC_MipsO32_FP64 : CC_MipsO32_FP32)
-             : CC_MipsN_VarArg;
+  return CC_Mips_FixedArg;
 }
 
 const MCPhysReg *MipsTargetLowering::MipsCC::shadowRegs() const {
Index: utils/TableGen/CallingConvEmitter.cpp
===================================================================
--- utils/TableGen/CallingConvEmitter.cpp
+++ utils/TableGen/CallingConvEmitter.cpp
@@ -35,23 +35,26 @@
 } // End anonymous namespace
 
 void CallingConvEmitter::run(raw_ostream &O) {
-
   std::vector<Record*> CCs = Records.getAllDerivedDefinitions("CallingConv");
-  
-  // Emit prototypes for all of the CC's so that they can forward ref each
-  // other.
+
+  // Emit prototypes for all of the non-custom CC's so that they can forward ref
+  // each other.
+  for (unsigned i = 0, e = CCs.size(); i != e; ++i) {
+    if (!CCs[i]->getValueAsBit("Custom")) {
+      O << "static bool " << CCs[i]->getName()
+        << "(unsigned ValNo, MVT ValVT,\n"
+        << std::string(CCs[i]->getName().size() + 13, ' ')
+        << "MVT LocVT, CCValAssign::LocInfo LocInfo,\n"
+        << std::string(CCs[i]->getName().size() + 13, ' ')
+        << "ISD::ArgFlagsTy ArgFlags, CCState &State);\n";
+    }
+  }
+
+  // Emit each non-custom calling convention description in full.
   for (unsigned i = 0, e = CCs.size(); i != e; ++i) {
-    O << "static bool " << CCs[i]->getName()
-      << "(unsigned ValNo, MVT ValVT,\n"
-      << std::string(CCs[i]->getName().size()+13, ' ')
-      << "MVT LocVT, CCValAssign::LocInfo LocInfo,\n"
-      << std::string(CCs[i]->getName().size()+13, ' ')
-      << "ISD::ArgFlagsTy ArgFlags, CCState &State);\n";
+    if (!CCs[i]->getValueAsBit("Custom"))
+      EmitCallingConv(CCs[i], O);
   }
-  
-  // Emit each calling convention description in full.
-  for (unsigned i = 0, e = CCs.size(); i != e; ++i)
-    EmitCallingConv(CCs[i], O);
 }