diff --git a/llvm/lib/Target/X86/X86CallingConv.td b/llvm/lib/Target/X86/X86CallingConv.td
index 0d087e057a2bd..215906d9df8b3 100644
--- a/llvm/lib/Target/X86/X86CallingConv.td
+++ b/llvm/lib/Target/X86/X86CallingConv.td
@@ -283,8 +283,10 @@ def RetCC_X86Common : CallingConv<[
             CCAssignToReg<[ZMM0,ZMM1,ZMM2,ZMM3]>>,
 
   // Long double types are always returned in FP0 (even with SSE),
-  // except on Win64.
-  CCIfNotSubtarget<"isTargetWin64()", CCIfType<[f80], CCAssignToReg<[FP0, FP1]>>>
+  // except on Win64 and UEFI64.
+  CCIfNotSubtarget<"isTargetWin64()",
+                    CCIfNotSubtarget<"isTargetUEFI64()",
+                    CCIfType<[f80], CCAssignToReg<[FP0, FP1]>>>>
 ]>;
 
 // X86-32 C return-value convention.
@@ -495,6 +497,9 @@ def RetCC_X86_64 : CallingConv<[
   // 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>
 ]>;
@@ -1085,6 +1090,9 @@ def CC_X86_64 : CallingConv<[
   // Mingw64 and native Win64 use Win64 CC
   CCIfSubtarget<"isTargetWin64()", CCDelegateTo<CC_X86_Win64_C>>,
 
+  // UEFI 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.cpp b/llvm/lib/Target/X86/X86RegisterInfo.cpp
index 29242c7059d5f..ef58c7619b243 100644
--- a/llvm/lib/Target/X86/X86RegisterInfo.cpp
+++ b/llvm/lib/Target/X86/X86RegisterInfo.cpp
@@ -60,6 +60,7 @@ X86RegisterInfo::X86RegisterInfo(const Triple &TT)
   // 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
@@ -227,7 +228,7 @@ X86RegisterInfo::getPointerRegClass(const MachineFunction &MF,
 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;
@@ -389,7 +390,7 @@ X86RegisterInfo::getCalleeSavedRegs(const MachineFunction *MF) const {
       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;
@@ -514,7 +515,7 @@ X86RegisterInfo::getCallPreservedMask(const MachineFunction &MF,
     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/X86RegisterInfo.h b/llvm/lib/Target/X86/X86RegisterInfo.h
index b3c03e8f2bc22..13a5fbf16e981 100644
--- a/llvm/lib/Target/X86/X86RegisterInfo.h
+++ b/llvm/lib/Target/X86/X86RegisterInfo.h
@@ -31,6 +31,10 @@ class X86RegisterInfo final : public X86GenRegisterInfo {
   ///
   bool IsWin64;
 
+  /// IsUEFI64 - Is UEFI 64 bit target.
+  ///
+  bool IsUEFI64;
+
   /// SlotSize - Stack slot size in bytes.
   ///
   unsigned SlotSize;
diff --git a/llvm/lib/Target/X86/X86Subtarget.h b/llvm/lib/Target/X86/X86Subtarget.h
index e0dd3565605b9..a0b182d3f4c9b 100644
--- a/llvm/lib/Target/X86/X86Subtarget.h
+++ b/llvm/lib/Target/X86/X86Subtarget.h
@@ -352,6 +352,7 @@ class X86Subtarget final : public X86GenSubtargetInfo {
     switch (CC) {
     // On Win64, all these conventions just use the default convention.
     case CallingConv::C:
+      return isTargetWin64() || isTargetUEFI64();
     case CallingConv::Fast:
     case CallingConv::Tail:
     case CallingConv::Swift: