[Driver] Add toolchain for LoongArch64 UEFI target

This patch is inspired by the X86_64's pr D159541.

Author: leecheechen

clang/lib/Basic/Targets.cpp

@@ -760,6 +760,9 @@ std::unique_ptr<TargetInfo> AllocateTarget(const llvm::Triple &Triple,
     case llvm::Triple::FreeBSD:
       return std::make_unique<FreeBSDTargetInfo<LoongArch64TargetInfo>>(Triple,
                                                                         Opts);
+    case llvm::Triple::UEFI:
+      return std::make_unique<UEFITargetInfo<LoongArch64TargetInfo>>(Triple,
+                                                                     Opts);
     default:
       return std::make_unique<LoongArch64TargetInfo>(Triple, Opts);
     }

clang/lib/Basic/Targets/LoongArch.h

@@ -13,6 +13,7 @@
 #ifndef LLVM_CLANG_LIB_BASIC_TARGETS_LOONGARCH_H
 #define LLVM_CLANG_LIB_BASIC_TARGETS_LOONGARCH_H
 
+#include "OSTargets.h"
 #include "clang/Basic/TargetInfo.h"
 #include "clang/Basic/TargetOptions.h"
 #include "llvm/Support/Compiler.h"
@@ -146,6 +147,8 @@ class LLVM_LIBRARY_VISIBILITY LoongArch64TargetInfo
     IntMaxType = Int64Type = SignedLong;
     HasUnalignedAccess = true;
     resetDataLayout("e-m:e-p:64:64-i64:64-i128:128-n32:64-S128");
+    if (Triple.isUEFI())
+      resetDataLayout("e-m:w-p:64:64-i64:64-i128:128-n32:64-S128");
     // TODO: select appropriate ABI.
     setABI("lp64d");
   }

llvm/lib/Target/LoongArch/LoongArchTargetMachine.cpp

@@ -56,8 +56,11 @@ static cl::opt<bool>
                            cl::init(false));
 
 static std::string computeDataLayout(const Triple &TT) {
-  if (TT.isArch64Bit())
+  if (TT.isArch64Bit()) {
+    if (TT.isUEFI())
+      return "e-m:w-p:64:64-i64:64-i128:128-n32:64-S128";
     return "e-m:e-p:64:64-i64:64-i128:128-n32:64-S128";
+  }
   assert(TT.isArch32Bit() && "only LA32 and LA64 are currently supported");
   return "e-m:e-p:32:32-i64:64-n32-S128";
 }