diff --git a/clang/include/clang/Basic/TargetOSMacros.def b/clang/include/clang/Basic/TargetOSMacros.def
index 58dce330f9c8f..f4f3276ad1c25 100644
--- a/clang/include/clang/Basic/TargetOSMacros.def
+++ b/clang/include/clang/Basic/TargetOSMacros.def
@@ -53,4 +53,7 @@ TARGET_OS(TARGET_OS_NANO, Triple.isWatchOS())
 TARGET_OS(TARGET_IPHONE_SIMULATOR, Triple.isSimulatorEnvironment())
 TARGET_OS(TARGET_OS_UIKITFORMAC, Triple.isMacCatalystEnvironment())
 
+// UEFI target.
+TARGET_OS(TARGET_OS_UEFI, Triple.isUEFI())
+
 #undef TARGET_OS
diff --git a/clang/lib/Basic/Targets/X86.h b/clang/lib/Basic/Targets/X86.h
index 205edcab9ccb3..fd38ae98fdfaf 100644
--- a/clang/lib/Basic/Targets/X86.h
+++ b/clang/lib/Basic/Targets/X86.h
@@ -835,8 +835,23 @@ class LLVM_LIBRARY_VISIBILITY UEFIX86_64TargetInfo
 public:
   UEFIX86_64TargetInfo(const llvm::Triple &Triple, const TargetOptions &Opts)
       : UEFITargetInfo<X86_64TargetInfo>(Triple, Opts) {
+    // The UEFI spec does not mandate specific C++ ABI, integer widths, or
+    // alignment. We are setting these defaults to match the Windows target as
+    // it is the only way to build EFI applications with Clang/LLVM today. We
+    // intend to offer flexibility by supporting choices that are not default in
+    // Windows target in the future.
     this->TheCXXABI.set(TargetCXXABI::Microsoft);
-    this->MaxTLSAlign = 8192u * this->getCharWidth();
+    LongWidth = LongAlign = 32;
+    DoubleAlign = LongLongAlign = 64;
+    LongDoubleWidth = LongDoubleAlign = 64;
+    LongDoubleFormat = &llvm::APFloat::IEEEdouble();
+    IntMaxType = SignedLongLong;
+    Int64Type = SignedLongLong;
+    SizeType = UnsignedLongLong;
+    PtrDiffType = SignedLongLong;
+    IntPtrType = SignedLongLong;
+    WCharType = UnsignedShort;
+    WIntType = UnsignedShort;
     this->resetDataLayout("e-m:w-p270:32:32-p271:32:32-p272:64:64-"
                           "i64:64-i128:128-f80:128-n8:16:32:64-S128");
   }
diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index f88d6202ad381..44e16ba4b4742 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -267,6 +267,7 @@ createTargetCodeGenInfo(CodeGenModule &CGM) {
                                                : X86AVXABILevel::None);
 
     switch (Triple.getOS()) {
+    case llvm::Triple::UEFI:
     case llvm::Triple::Win32:
       return createWinX86_64TargetCodeGenInfo(CGM, AVXLevel);
     default:
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index fe172d923ac07..2bc1cecb53c38 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -5959,7 +5959,8 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
   // We turn strict aliasing off by default if we're Windows MSVC since MSVC
   // doesn't do any TBAA.
   if (!Args.hasFlag(options::OPT_fstrict_aliasing, StrictAliasingAliasOption,
-                    options::OPT_fno_strict_aliasing, !IsWindowsMSVC))
+                    options::OPT_fno_strict_aliasing,
+                    !IsWindowsMSVC && !IsUEFI))
     CmdArgs.push_back("-relaxed-aliasing");
   if (Args.hasFlag(options::OPT_fno_pointer_tbaa, options::OPT_fpointer_tbaa,
                    false))
diff --git a/clang/test/Preprocessor/init.c b/clang/test/Preprocessor/init.c
index 1ac325d444662..4c8d519c2b664 100644
--- a/clang/test/Preprocessor/init.c
+++ b/clang/test/Preprocessor/init.c
@@ -2835,6 +2835,7 @@
 // RISCV64-LINUX: #define unix 1
 
 // RUN: %clang_cc1 -dM -triple=x86_64-uefi -E /dev/null | FileCheck -match-full-lines -check-prefix UEFI %s
+// RUN: %clang_cc1 -dM -triple=x86_64-unknown-uefi -E /dev/null | FileCheck -match-full-lines -check-prefix UEFI %s
 
 // UEFI: #define __UEFI__ 1