Index: clang/lib/Driver/ToolChains/Clang.cpp
===================================================================
--- clang/lib/Driver/ToolChains/Clang.cpp
+++ clang/lib/Driver/ToolChains/Clang.cpp
@@ -4721,9 +4721,11 @@
   // Select the appropriate action.
   RewriteKind rewriteKind = RK_None;
 
+  bool DefaultUnified = Triple.isPS4();
   bool UnifiedLTO =
           Args.hasFlag(options::OPT_funified_lto,
-                       options::OPT_fno_unified_lto, false);
+                       options::OPT_fno_unified_lto,
+                       DefaultUnified);
   if (UnifiedLTO)
     CmdArgs.push_back("-funified-lto");
 
@@ -7286,7 +7288,8 @@
 
   bool DefaultsSplitLTOUnit =
       (WholeProgramVTables || SanitizeArgs.needsLTO()) &&
-      (LTOMode == LTOK_Full || TC.canSplitThinLTOUnit());
+      (LTOMode == LTOK_Full || TC.canSplitThinLTOUnit()) ||
+       UnifiedLTO;
   bool SplitLTOUnit =
       Args.hasFlag(options::OPT_fsplit_lto_unit,
                    options::OPT_fno_split_lto_unit, DefaultsSplitLTOUnit);
Index: clang/lib/Frontend/CompilerInvocation.cpp
===================================================================
--- clang/lib/Frontend/CompilerInvocation.cpp
+++ clang/lib/Frontend/CompilerInvocation.cpp
@@ -1777,6 +1777,12 @@
     else if (S != "full")
       Diags.Report(diag::err_drv_invalid_value) << A->getAsString(Args) << S;
   }
+
+  if (Opts.UnifiedLTO && Opts.PrepareForLTO) {
+    Opts.PrepareForThinLTO = true;
+    Opts.PrepareForLTO = false;
+  }
+
   if (Arg *A = Args.getLastArg(OPT_fthinlto_index_EQ)) {
     if (IK.getLanguage() != Language::LLVM_IR)
       Diags.Report(diag::err_drv_argument_only_allowed_with)
Index: clang/test/CodeGen/split-lto-unit.c
===================================================================
--- clang/test/CodeGen/split-lto-unit.c
+++ clang/test/CodeGen/split-lto-unit.c
@@ -1,6 +1,7 @@
 // ; Check that -flto=thin without -fsplit-lto-unit has EnableSplitLTOUnit = 0
 // RUN: %clang_cc1 -flto=thin -emit-llvm-bc < %s | llvm-dis -o - | FileCheck %s
 // RUN: %clang_cc1 -flto=thin -emit-llvm < %s | FileCheck %s
+// RUN: %clang_cc1 -flto=thin -funified-lto -triple=x86_64-scei-ps4 -emit-llvm-bc < %s | llvm-dis -o - | FileCheck %s
 // CHECK: !{i32 1, !"EnableSplitLTOUnit", i32 0}
 //
 // ; Check that -flto=thin with -fsplit-lto-unit has EnableSplitLTOUnit = 1
@@ -12,4 +13,9 @@
 // RUN: %clang_cc1 -flto -triple x86_64-pc-linux-gnu -emit-llvm-bc < %s | llvm-dis -o - | FileCheck %s --implicit-check-not="EnableSplitLTOUnit" --check-prefix=SPLIT
 // RUN: %clang_cc1 -flto -triple x86_64-pc-linux-gnu -emit-llvm < %s | FileCheck %s --implicit-check-not="EnableSplitLTOUnit" --check-prefix=SPLIT
 
+// ; Check that regular LTO has EnableSplitLTOUnit = 1, if using distinct pipelines. For unified pipelines, use EnableSplitLTOUnit = 0.
+// RUN: %clang_cc1 -flto -triple x86_64-pc-linux-gnu -emit-llvm-bc < %s | llvm-dis -o - | FileCheck %s --implicit-check-not="EnableSplitLTOUnit" --check-prefix=SPLIT
+// RUN: %clang_cc1 -flto -funified-lto -triple x86_64-scei-ps4 -emit-llvm-bc < %s | llvm-dis -o - | FileCheck %s --implicit-check-not="EnableSplitLTOUnit"
+// RUN: %clang_cc1 -flto=thin -funified-lto -triple x86_64-pc-linux-gnu -emit-llvm-bc < %s | llvm-dis -o - | FileCheck %s --implicit-check-not="EnableSplitLTOUnit" --check-prefix=SPLIT
+
 int main(void) {}
Index: clang/test/Driver/split-lto-unit.c
===================================================================
--- clang/test/Driver/split-lto-unit.c
+++ clang/test/Driver/split-lto-unit.c
@@ -5,8 +5,10 @@
 // RUN: %clang -target x86_64-unknown-linux -### %s -flto=thin -fno-split-lto-unit -fsanitize=cfi 2>&1 | FileCheck --check-prefix=ERROR2 %s
 // RUN: %clang -target x86_64-apple-darwin13.3.0 -### %s -fwhole-program-vtables -flto=full 2>&1 | FileCheck --check-prefix=UNIT %s
 // RUN: %clang -target x86_64-apple-darwin13.3.0 -### %s -fwhole-program-vtables -flto=thin 2>&1 | FileCheck --check-prefix=NOUNIT %s
-// RUN: %clang -target x86_64-scei-ps4 -### %s -fwhole-program-vtables -flto=full 2>&1 | FileCheck --check-prefix=UNIT %s
-// RUN: %clang -target x86_64-scei-ps4 -### %s -fwhole-program-vtables -flto=thin 2>&1 | FileCheck --check-prefix=NOUNIT %s
+// RUN: %clang -target x86_64-scei-ps4 -### %s -fwhole-program-vtables -flto=full -funified-lto 2>&1 | FileCheck --check-prefix=UNIT %s
+// RUN: %clang -target x86_64-scei-ps4 -### %s -fwhole-program-vtables -flto=thin -funified-lto 2>&1 | FileCheck --check-prefix=UNIT %s
+// RUN: %clang -target x86_64-unknown-linux -### %s -fwhole-program-vtables -flto=full -funified-lto 2>&1 | FileCheck --check-prefix=UNIT %s
+// RUN: %clang -target x86_64-unknown-linux -### %s -fwhole-program-vtables -flto=thin -funified-lto 2>&1 | FileCheck --check-prefix=UNIT %s
 
 // UNIT: "-fsplit-lto-unit"
 // NOUNIT-NOT: "-fsplit-lto-unit"