[clang] Add -funique-source-file-output-paths option

clang/docs/UsersManual.rst

@@ -2341,10 +2341,11 @@ are listed below.
 
    When enabled, allows the compiler to assume that each object file
    passed to the linker has a unique identifier. The identifier for
-   an object file is either the source file path or the value of the
-   argument `-funique-source-file-identifier` if specified. This is
-   useful for reducing link times when doing ThinLTO in combination with
-   whole-program devirtualization or CFI.
+   an object file is either the source file path, the output file path
+   if the ``-funique-source-file-output-paths`` argument is passed, or
+   the value of the argument ``-funique-source-file-identifier`` if
+   specified. This is useful for reducing link times when doing ThinLTO
+   in combination with whole-program devirtualization or CFI.
 
    The full source path or identifier passed to the compiler must be
    unique. This means that, for example, the following is a usage error:
@@ -2371,9 +2372,14 @@ are listed below.
 
 .. option:: -funique-source-file-identifier=IDENTIFIER
 
-   Used with `-funique-source-file-names` to specify a source file
+   Used with ``-funique-source-file-names`` to specify a source file
    identifier.
 
+.. option:: -funique-source-file-output-paths
+
+   Used with ``-funique-source-file-names`` to specify the output path
+   as the source file identifier.
+
 .. option:: -fforce-emit-vtables
 
    In order to improve devirtualization, forces emitting of vtables even in

clang/include/clang/Basic/DiagnosticDriverKinds.td

@@ -890,4 +890,7 @@ def warn_drv_gcc_install_dir_libstdcxx : Warning<
     "future releases of the clang compiler will prefer GCC installations "
     "containing libstdc++ include directories; '%0' would be chosen over '%1'">,
     InGroup<DiagGroup<"gcc-install-dir-libstdcxx">>;
+
+def err_drv_no_output_filename : Error<
+  "option '%0' requires an output file name">;
 }

clang/include/clang/Driver/Options.td

@@ -4354,6 +4354,8 @@ def unique_source_file_identifier_EQ: Joined<["-"], "funique-source-file-identif
   HelpText<"Specify the source file identifier for -funique-source-file-names; "
            "uses the source file path if not specified">,
   MarshallingInfoString<CodeGenOpts<"UniqueSourceFileIdentifier">>;
+def funique_source_file_output_paths: Joined<["-"], "funique-source-file-output-paths">, Group<f_Group>,
+  HelpText<"Use the output path as the source file identifier for -funique-source-file-names">;
 def funsigned_bitfields : Flag<["-"], "funsigned-bitfields">, Group<f_Group>;
 def funsigned_char : Flag<["-"], "funsigned-char">, Group<f_Group>;
 def fno_unsigned_char : Flag<["-"], "fno-unsigned-char">;

clang/lib/Driver/ToolChains/Clang.cpp

@@ -7578,11 +7578,21 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
 
   if (Args.hasFlag(options::OPT_funique_source_file_names,
                    options::OPT_fno_unique_source_file_names, false)) {
-    if (Arg *A = Args.getLastArg(options::OPT_unique_source_file_identifier_EQ))
-      A->render(Args, CmdArgs);
-    else
+    Arg *A = Args.getLastArg(options::OPT_unique_source_file_identifier_EQ,
+                             options::OPT_funique_source_file_output_paths);
+    if (!A) {
       CmdArgs.push_back(Args.MakeArgString(
           Twine("-funique-source-file-identifier=") + Input.getBaseInput()));
+    } else if (A->getOption().matches(
+                   options::OPT_funique_source_file_output_paths)) {
+      if (Output.isFilename())
+        CmdArgs.push_back(Args.MakeArgString(
+            Twine("-funique-source-file-identifier=") + Output.getFilename()));
+      else
+        D.Diag(diag::err_drv_no_output_filename) << A->getSpelling();
+    } else {
+      A->render(Args, CmdArgs);
+    }
   }
 
   // Setup statistics file output.

clang/test/Driver/unique-source-file-names.c

@@ -9,3 +9,9 @@
 
 // ID: "-cc1"
 // ID: "-funique-source-file-identifier=foo"
+
+// RUN: %clang -funique-source-file-names -funique-source-file-output-paths -o out.o -c -### %s 2> %t
+// RUN: FileCheck --check-prefix=OUTPUT < %t %s
+
+// OUTPUT: "-cc1"
+// OUTPUT: "-funique-source-file-identifier=out.o"