Index: include/clang/Driver/Options.td
===================================================================
--- include/clang/Driver/Options.td
+++ include/clang/Driver/Options.td
@@ -957,19 +957,19 @@
 def flat__namespace : Flag<["-"], "flat_namespace">;
 def flax_vector_conversions : Flag<["-"], "flax-vector-conversions">, Group<f_Group>;
 def flimited_precision_EQ : Joined<["-"], "flimited-precision=">, Group<f_Group>;
-def flto_EQ : Joined<["-"], "flto=">, Flags<[CC1Option]>, Group<f_Group>,
+def flto_EQ : Joined<["-"], "flto=">, Flags<[CoreOption, CC1Option]>, Group<f_Group>,
   HelpText<"Set LTO mode to either 'full' or 'thin'">;
 def flto : Flag<["-"], "flto">, Flags<[CoreOption, CC1Option]>, Group<f_Group>,
   HelpText<"Enable LTO in 'full' mode">;
 def fno_lto : Flag<["-"], "fno-lto">, Group<f_Group>,
   HelpText<"Disable LTO mode (default)">;
 def flto_jobs_EQ : Joined<["-"], "flto-jobs=">,
-  Flags<[CC1Option]>, Group<f_Group>,
+  Flags<[CoreOption, CC1Option]>, Group<f_Group>,
   HelpText<"Controls the backend parallelism of -flto=thin (default "
            "of 0 means the number of threads will be derived from "
            "the number of CPUs detected)">;
 def fthinlto_index_EQ : Joined<["-"], "fthinlto-index=">,
-  Flags<[CC1Option]>, Group<f_Group>,
+  Flags<[CoreOption, CC1Option]>, Group<f_Group>,
   HelpText<"Perform ThinLTO importing using provided function summary index">;
 def fmacro_backtrace_limit_EQ : Joined<["-"], "fmacro-backtrace-limit=">,
                                 Group<f_Group>, Flags<[DriverOption, CoreOption]>;
Index: test/Driver/cl-lto.c
===================================================================
--- /dev/null
+++ test/Driver/cl-lto.c
@@ -0,0 +1,25 @@
+// -flto causes a switch to llvm-bc object files.
+// RUN: %clang_cl -ccc-print-phases -c -flto -- %s 2> %t
+// RUN: FileCheck -check-prefix=CHECK-COMPILE-ACTIONS < %t %s
+//
+// CHECK-COMPILE-ACTIONS: 2: compiler, {1}, ir
+// CHECK-COMPILE-ACTIONS: 3: backend, {2}, lto-bc
+
+// RUN: %clang_cl -ccc-print-phases -flto -- %s 2> %t
+// RUN: FileCheck -check-prefix=CHECK-COMPILELINK-ACTIONS < %t %s
+//
+// CHECK-COMPILELINK-ACTIONS: 0: input, "{{.*}}lto.c", c
+// CHECK-COMPILELINK-ACTIONS: 1: preprocessor, {0}, cpp-output
+// CHECK-COMPILELINK-ACTIONS: 2: compiler, {1}, ir
+// CHECK-COMPILELINK-ACTIONS: 3: backend, {2}, lto-bc
+// CHECK-COMPILELINK-ACTIONS: 4: linker, {3}, image
+
+// llvm-bc and llvm-ll outputs need to match regular suffixes
+// (unfortunately).
+// RUN: %clang_cl -### -flto -- %s 2> %t
+// RUN: FileCheck -check-prefix=CHECK-COMPILELINK-SUFFIXES < %t %s
+//
+// CHECK-COMPILELINK-SUFFIXES: "-emit-llvm-bc"
+// CHECK-COMPILELINK-SUFFIXES-SAME: "-o" "{{.*}}cl-lto{{[^ ]*}}.obj"
+// CHECK-COMPILELINK-SUFFIXES-SAME: "-x" "c" "{{.*}}cl-lto.c"
+// CHECK-COMPILELINK-SUFFIXES: "{{.*}}cl-lto.{{(exe)}}" {{.*}}"{{.*}}cl-lto{{[^ ]*}}.obj"
Index: test/Driver/cl-thinlto.c
===================================================================
--- /dev/null
+++ test/Driver/cl-thinlto.c
@@ -0,0 +1,33 @@
+// -flto=thin causes a switch to llvm-bc object files.
+// RUN: %clang_cl -ccc-print-phases -c -flto=thin -- %s 2> %t
+// RUN: FileCheck -check-prefix=CHECK-COMPILE-ACTIONS < %t %s
+//
+// CHECK-COMPILE-ACTIONS: 2: compiler, {1}, ir
+// CHECK-COMPILE-ACTIONS: 3: backend, {2}, lto-bc
+
+// RUN: %clang_cl -ccc-print-phases -flto=thin -- %s 2> %t
+// RUN: FileCheck -check-prefix=CHECK-COMPILELINK-ACTIONS < %t %s
+//
+// CHECK-COMPILELINK-ACTIONS: 0: input, "{{.*}}thinlto.c", c
+// CHECK-COMPILELINK-ACTIONS: 1: preprocessor, {0}, cpp-output
+// CHECK-COMPILELINK-ACTIONS: 2: compiler, {1}, ir
+// CHECK-COMPILELINK-ACTIONS: 3: backend, {2}, lto-bc
+// CHECK-COMPILELINK-ACTIONS: 4: linker, {3}, image
+
+// -flto=thin should take precedence over earlier -fno-lto and -flto=full.
+// RUN: %clang_cl -### -fuse-ld=lld -flto=full -fno-lto -flto=thin -- %s 2> %t
+// RUN: FileCheck -check-prefix=CHECK-LINK-THIN-ACTION < %t %s
+//
+// CHECK-LINK-THIN-ACTION: "-cc1"{{.*}}"-flto=thin"
+
+// Check that subsequent -flto=full takes precedence
+// RUN: %clang_cl -### -flto=thin -flto=full -- %s 2> %t
+// RUN: FileCheck -check-prefix=CHECK-LINK-FULL-ACTION < %t %s
+//
+// CHECK-LINK-FULL-ACTION: "-cc1"{{.*}}"-flto=full"
+
+// Check that subsequent -fno-lto takes precedence
+// RUN: %clang_cl -### %s -flto=thin -fno-lto 2> %t
+// RUN: FileCheck -check-prefix=CHECK-LINK-NOLTO-ACTION < %t %s
+//
+// CHECK-LINK-NOLTO-ACTION-NOT: "-cc1"{{.*}}"-flto"