Index: lld/ELF/Config.h
===================================================================
--- lld/ELF/Config.h
+++ lld/ELF/Config.h
@@ -18,6 +18,7 @@
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/StringSet.h"
 #include "llvm/BinaryFormat/ELF.h"
+#include "llvm/LTO/LTO.h"
 #include "llvm/Option/ArgList.h"
 #include "llvm/Support/CachePruning.h"
 #include "llvm/Support/CodeGen.h"
@@ -414,6 +415,8 @@
   // this means to map the primary and thread stacks as PROT_MTE. Note: This is
   // not supported on Android 11 & 12.
   bool androidMemtagStack;
+  // When using a unified pre-link LTO pipeline, specify the backend LTO mode.
+  llvm::lto::LTO::LTOKind forceLTOMode = llvm::lto::LTO::LTOK_Default;
 
   unsigned threadCount;
 
Index: lld/ELF/Driver.cpp
===================================================================
--- lld/ELF/Driver.cpp
+++ lld/ELF/Driver.cpp
@@ -1489,6 +1489,19 @@
     config->mllvmOpts.emplace_back(arg->getValue());
   }
 
+  config->forceLTOMode = llvm::lto::LTO::LTOK_Default;
+  if (auto *arg = args.getLastArg(OPT_lto)) {
+    StringRef s = arg->getValue();
+    if (s == "thin")
+      config->forceLTOMode = llvm::lto::LTO::LTOK_UnifiedThin;
+    else if (s == "full")
+      config->forceLTOMode = llvm::lto::LTO::LTOK_UnifiedRegular;
+    else if (s == "default")
+      config->forceLTOMode = llvm::lto::LTO::LTOK_Default;
+    else
+      error("unknown LTO mode: " + s);
+  }
+
   // --threads= takes a positive integer and provides the default value for
   // --thinlto-jobs=. If unspecified, cap the number of threads since
   // overhead outweighs optimization for used parallel algorithms for the
Index: lld/ELF/LTO.cpp
===================================================================
--- lld/ELF/LTO.cpp
+++ lld/ELF/LTO.cpp
@@ -206,8 +206,8 @@
         config->thinLTOEmitImportsFiles);
   }
 
-  ltoObj = std::make_unique<lto::LTO>(createConfig(), backend,
-                                       config->ltoPartitions);
+  ltoObj = std::make_unique<lto::LTO>(
+      createConfig(), backend, config->ltoPartitions, config->forceLTOMode);
 
   // Initialize usedStartStop.
   if (ctx.bitcodeFiles.empty())
Index: lld/ELF/Options.td
===================================================================
--- lld/ELF/Options.td
+++ lld/ELF/Options.td
@@ -577,6 +577,9 @@
 def: Flag<["-"], "V">, Alias<v>, HelpText<"Alias for -v">;
 
 // LTO-related options.
+
+def lto: J<"lto=">, HelpText<"Set LTO backend">,
+                 MetaVarName<"[full,thin]">;
 def lto_aa_pipeline: JJ<"lto-aa-pipeline=">,
   HelpText<"AA pipeline to run during LTO. Used in conjunction with -lto-newpm-passes">;
 def lto_debug_pass_manager: FF<"lto-debug-pass-manager">,
Index: lld/test/ELF/lto/unified-lto.ll
===================================================================
--- /dev/null
+++ lld/test/ELF/lto/unified-lto.ll
@@ -0,0 +1,35 @@
+; REQUIRES: x86
+; RUN: opt -thinlto-bc -thinlto-split-lto-unit -unified-lto %s -o %t0.o
+; RUN: opt -thinlto-bc -thinlto-split-lto-unit %s -o %t1.o
+; RUN: ld.lld --lto=full %t0.o -o %t0
+; RUN: llvm-readelf -s --symbols %t0 | FileCheck %s --check-prefix=FULL
+; RUN: ld.lld --lto=thin %t0.o -o %t0
+; RUN: llvm-readelf -s --symbols %t0 | FileCheck %s --check-prefix=THIN
+; RUN: ld.lld --lto=default %t0.o -o %t0
+; RUN: llvm-readelf -s --symbols %t0 | FileCheck %s --check-prefix=THIN
+; RUN: ld.lld --lto=default %t1.o -o %t1
+; RUN: llvm-readelf -s --symbols %t1 | FileCheck %s --check-prefix=THIN
+; RUN: ld.lld %t0.o -o %t0 2>&1 | count 0
+; RUN: llvm-readelf -s --symbols %t0 | FileCheck %s --check-prefix=THIN
+; RUN: not ld.lld --lto=unknown %t1.o -o /dev/null 2>&1 | \
+; RUN:   FileCheck --implicit-check-not=error: --check-prefix=ERR %s
+; ERR: error: unknown LTO mode: unknown
+
+; FULL:      Symbol table '.symtab' contains 3 entries:
+; FULL-NEXT: Num:    Value          Size Type    Bind   Vis       Ndx Name
+; FULL-NEXT: 0: 0000000000000000     0 NOTYPE  LOCAL  DEFAULT   UND
+; FULL-NEXT: 1: 0000000000000000     0 FILE    LOCAL  DEFAULT   ABS ld-temp.o
+; FULL-NEXT: 2: 0000000000201120     1 FUNC    GLOBAL DEFAULT     1 _start
+
+; THIN:      Symbol table '.symtab' contains 3 entries:
+; THIN-NEXT: Num:    Value          Size Type    Bind   Vis       Ndx Name
+; THIN-NEXT: 0: 0000000000000000     0 NOTYPE  LOCAL  DEFAULT   UND
+; THIN-NEXT: 1: 0000000000000000     0 FILE    LOCAL  DEFAULT   ABS unified-lto.ll
+; THIN-NEXT: 2: 0000000000201120     1 FUNC    GLOBAL DEFAULT     1 _start
+
+target triple = "x86_64-unknown-linux-gnu"
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+
+define void @_start() {
+  ret void
+}