Index: clang/lib/Driver/Driver.cpp
===================================================================
--- clang/lib/Driver/Driver.cpp
+++ clang/lib/Driver/Driver.cpp
@@ -600,8 +600,9 @@
 
   StringRef LTOName("full");
 
-  const Arg *A = Args.getLastArg(OptEq);
-  if (A)
+  const Arg *A = Args.getLastArg(OptEq, OptPos);
+  // Use the OptEq only if it is after the -flto option.
+  if (A && A->getOption().matches(OptEq))
     LTOName = A->getValue();
 
   LTOMode = llvm::StringSwitch<LTOKind>(LTOName)
Index: clang/lib/Driver/ToolChains/Clang.cpp
===================================================================
--- clang/lib/Driver/ToolChains/Clang.cpp
+++ clang/lib/Driver/ToolChains/Clang.cpp
@@ -4491,18 +4491,8 @@
       CmdArgs.push_back("-emit-llvm-uselists");
 
     if (IsUsingLTO) {
-      if (!IsDeviceOffloadAction) {
-        if (Args.hasArg(options::OPT_flto))
-          CmdArgs.push_back("-flto");
-        else {
-          if (D.getLTOMode() == LTOK_Thin)
-            CmdArgs.push_back("-flto=thin");
-          else
-            CmdArgs.push_back("-flto=full");
-        }
-        CmdArgs.push_back("-flto-unit");
-      } else if (Triple.isAMDGPU()) {
-        // Only AMDGPU supports device-side LTO
+      // Only AMDGPU supports device-side LTO.
+      if (!IsDeviceOffloadAction || Triple.isAMDGPU()) {
         assert(LTOMode == LTOK_Full || LTOMode == LTOK_Thin);
         CmdArgs.push_back(Args.MakeArgString(
             Twine("-flto=") + (LTOMode == LTOK_Thin ? "thin" : "full")));
Index: clang/test/Driver/amdgpu-toolchain.c
===================================================================
--- clang/test/Driver/amdgpu-toolchain.c
+++ clang/test/Driver/amdgpu-toolchain.c
@@ -12,5 +12,5 @@
 
 // RUN: %clang -### -target amdgcn-amd-amdhsa -mcpu=gfx906 -nogpulib \
 // RUN:   -flto %s 2>&1 | FileCheck -check-prefix=LTO %s
-// LTO: clang{{.*}} "-flto"
+// LTO: clang{{.*}} "-flto=full"
 // LTO: ld.lld{{.*}}
Index: clang/test/Driver/lto.c
===================================================================
--- clang/test/Driver/lto.c
+++ clang/test/Driver/lto.c
@@ -85,3 +85,21 @@
 // FLTO-AUTO: -flto=full
 // FLTO-JOBSERVER: -flto=full
 //
+
+// Pass the last -flto argument.
+// RUN: %clang -target x86_64-unknown-linux -### %s -flto=thin -flto 2>&1 | \
+// RUN: FileCheck --check-prefix=FLTO-FULL %s
+// RUN: %clang -target x86_64-unknown-linux -### %s -flto=thin -flto=full 2>&1 | \
+// RUN: FileCheck --check-prefix=FLTO-FULL %s
+// RUN: %clang -target x86_64-unknown-linux -### %s -flto -flto=thin 2>&1 | \
+// RUN: FileCheck --check-prefix=FLTO-THIN %s
+//
+// FLTO-FULL-NOT: -flto=thin
+// FLTO-FULL: -flto=full
+// FLTO-FULL-NOT: -flto=thin
+//
+// FLTO-THIN-NOT: -flto=full
+// FLTO-THIN-NOT: "-flto"
+// FLTO-THIN: -flto=thin
+// FLTO-THIN-NOT: "-flto"
+// FLTO-THIN-NOT: -flto=full