diff --git a/llvm/lib/Target/X86/MCTargetDesc/X86MCTargetDesc.cpp b/llvm/lib/Target/X86/MCTargetDesc/X86MCTargetDesc.cpp
--- a/llvm/lib/Target/X86/MCTargetDesc/X86MCTargetDesc.cpp
+++ b/llvm/lib/Target/X86/MCTargetDesc/X86MCTargetDesc.cpp
@@ -445,7 +445,7 @@
     // Force the use of an ELF container.
     MAI = new X86ELFMCAsmInfo(TheTriple);
   } else if (TheTriple.isWindowsMSVCEnvironment() ||
-             TheTriple.isWindowsCoreCLREnvironment()) {
+             TheTriple.isWindowsCoreCLREnvironment() || TheTriple.isUEFI()) {
     if (Options.getAssemblyLanguage().equals_insensitive("masm"))
       MAI = new X86MCAsmInfoMicrosoftMASM(TheTriple);
     else
@@ -453,8 +453,6 @@
   } else if (TheTriple.isOSCygMing() ||
              TheTriple.isWindowsItaniumEnvironment()) {
     MAI = new X86MCAsmInfoGNUCOFF(TheTriple);
-  } else if (TheTriple.isUEFI()) {
-    MAI = new X86MCAsmInfoGNUCOFF(TheTriple);
   } else {
     // The default is ELF.
     MAI = new X86ELFMCAsmInfo(TheTriple);
diff --git a/llvm/lib/Target/X86/X86CallingConv.td b/llvm/lib/Target/X86/X86CallingConv.td
--- a/llvm/lib/Target/X86/X86CallingConv.td
+++ b/llvm/lib/Target/X86/X86CallingConv.td
@@ -521,6 +521,9 @@
   // Mingw64 and native Win64 use Win64 CC
   CCIfSubtarget<"isTargetWin64()", CCDelegateTo<RetCC_X86_Win64_C>>,
 
+  // UEFI64 uses Win64 CC
+  CCIfSubtarget<"isTargetUEFI64()", CCDelegateTo<RetCC_X86_Win64_C>>,
+
   // Otherwise, drop to normal X86-64 CC
   CCDelegateTo<RetCC_X86_64_C>
 ]>;
@@ -1127,6 +1130,9 @@
   // Mingw64 and native Win64 use Win64 CC
   CCIfSubtarget<"isTargetWin64()", CCDelegateTo<CC_X86_Win64_C>>,
 
+  // UEFI64 uses Win64 CC
+  CCIfSubtarget<"isTargetUEFI64()", CCDelegateTo<CC_X86_Win64_C>>,
+
   // Otherwise, drop to normal X86-64 CC
   CCDelegateTo<CC_X86_64_C>
 ]>;
diff --git a/llvm/lib/Target/X86/X86RegisterInfo.h b/llvm/lib/Target/X86/X86RegisterInfo.h
--- a/llvm/lib/Target/X86/X86RegisterInfo.h
+++ b/llvm/lib/Target/X86/X86RegisterInfo.h
@@ -27,10 +27,14 @@
   ///
   bool Is64Bit;
 
-  /// IsWin64 - Is the target on of win64 flavours
+  /// IsWin64 - Is the target one of win64 flavours
   ///
   bool IsWin64;
 
+  /// IsUEFI64 - Is this UEFI 64 bit target
+  ///
+  bool IsUEFI64;
+
   /// SlotSize - Stack slot size in bytes.
   ///
   unsigned SlotSize;
diff --git a/llvm/lib/Target/X86/X86RegisterInfo.cpp b/llvm/lib/Target/X86/X86RegisterInfo.cpp
--- a/llvm/lib/Target/X86/X86RegisterInfo.cpp
+++ b/llvm/lib/Target/X86/X86RegisterInfo.cpp
@@ -55,6 +55,7 @@
   // Cache some information.
   Is64Bit = TT.isArch64Bit();
   IsWin64 = Is64Bit && TT.isOSWindows();
+  IsUEFI64 = Is64Bit && TT.isUEFI();
 
   // Use a callee-saved register as the base pointer.  These registers must
   // not conflict with any ABI requirements.  For example, in 32-bit mode PIC
@@ -232,7 +233,7 @@
 const TargetRegisterClass *
 X86RegisterInfo::getGPRsForTailCall(const MachineFunction &MF) const {
   const Function &F = MF.getFunction();
-  if (IsWin64 || (F.getCallingConv() == CallingConv::Win64))
+  if (IsWin64 || IsUEFI64 || (F.getCallingConv() == CallingConv::Win64))
     return &X86::GR64_TCW64RegClass;
   else if (Is64Bit)
     return &X86::GR64_TCRegClass;
@@ -331,7 +332,7 @@
   }
   case CallingConv::X86_RegCall:
     if (Is64Bit) {
-      if (IsWin64) {
+      if (IsWin64 || IsUEFI64) {
         return (HasSSE ? CSR_Win64_RegCall_SaveList :
                          CSR_Win64_RegCall_NoSSE_SaveList);
       } else {
@@ -391,7 +392,7 @@
       return IsWin64 ? CSR_Win64_SwiftError_SaveList
                      : CSR_64_SwiftError_SaveList;
 
-    if (IsWin64)
+    if (IsWin64 || IsUEFI64)
       return HasSSE ? CSR_Win64_SaveList : CSR_Win64_NoSSE_SaveList;
     if (CallsEHReturn)
       return CSR_64EHRet_SaveList;
@@ -451,7 +452,7 @@
   }
   case CallingConv::X86_RegCall:
     if (Is64Bit) {
-      if (IsWin64) {
+      if (IsWin64 || IsUEFI64) {
         return (HasSSE ? CSR_Win64_RegCall_RegMask :
                          CSR_Win64_RegCall_NoSSE_RegMask);
       } else {
@@ -509,7 +510,7 @@
     if (IsSwiftCC)
       return IsWin64 ? CSR_Win64_SwiftError_RegMask : CSR_64_SwiftError_RegMask;
 
-    return IsWin64 ? CSR_Win64_RegMask : CSR_64_RegMask;
+    return (IsWin64 || IsUEFI64) ? CSR_Win64_RegMask : CSR_64_RegMask;
   }
 
   return CSR_32_RegMask;
diff --git a/llvm/lib/Target/X86/X86Subtarget.h b/llvm/lib/Target/X86/X86Subtarget.h
--- a/llvm/lib/Target/X86/X86Subtarget.h
+++ b/llvm/lib/Target/X86/X86Subtarget.h
@@ -334,6 +334,10 @@
 
   bool isOSWindows() const { return TargetTriple.isOSWindows(); }
 
+  bool isUEFI() const { return TargetTriple.isUEFI(); }
+
+  bool isTargetUEFI64() const { return Is64Bit && isUEFI(); }
+
   bool isTargetWin64() const { return Is64Bit && isOSWindows(); }
 
   bool isTargetWin32() const { return !Is64Bit && isOSWindows(); }
@@ -349,7 +353,8 @@
 
   bool isCallingConvWin64(CallingConv::ID CC) const {
     switch (CC) {
-    // On Win64, all these conventions just use the default convention.
+    // On Win64 and UEFI64, all these conventions just use the default
+    // convention.
     case CallingConv::C:
     case CallingConv::Fast:
     case CallingConv::Tail:
@@ -360,7 +365,7 @@
     case CallingConv::X86_ThisCall:
     case CallingConv::X86_VectorCall:
     case CallingConv::Intel_OCL_BI:
-      return isTargetWin64();
+      return isTargetWin64() || isTargetUEFI64();
     // This convention allows using the Win64 convention on other targets.
     case CallingConv::Win64:
       return true;