Index: include/clang/Driver/Options.td
===================================================================
--- include/clang/Driver/Options.td
+++ include/clang/Driver/Options.td
@@ -1741,7 +1741,8 @@
 def fno_split_dwarf_inlining: Flag<["-"], "fno-split-dwarf-inlining">, Group<f_Group>,
   Flags<[CC1Option]>;
 def fdebug_prefix_map_EQ
-  : Joined<["-"], "fdebug-prefix-map=">, Group<f_Group>, Flags<[CC1Option]>,
+  : Joined<["-"], "fdebug-prefix-map=">, Group<f_Group>,
+    Flags<[CC1Option,CC1AsOption]>,
     HelpText<"remap file source paths in debug info">;
 def g_Flag : Flag<["-"], "g">, Group<g_Group>,
   HelpText<"Generate source-level debug information">;
Index: lib/Driver/ToolChains/Clang.cpp
===================================================================
--- lib/Driver/ToolChains/Clang.cpp
+++ lib/Driver/ToolChains/Clang.cpp
@@ -600,6 +600,18 @@
   }
 }
 
+/// Add a CC1 and CC1AS option to specify the debug file path prefix map.
+static void addDebugPrefixMapArg(const Driver &D, const ArgList &Args, ArgStringList &CmdArgs) {
+  for (const Arg *A : Args.filtered(options::OPT_fdebug_prefix_map_EQ)) {
+    StringRef Map = A->getValue();
+    if (Map.find('=') == StringRef::npos)
+      D.Diag(diag::err_drv_invalid_argument_to_fdebug_prefix_map) << Map;
+    else
+      CmdArgs.push_back(Args.MakeArgString("-fdebug-prefix-map=" + Map));
+    A->claim();
+  }
+}
+
 /// Vectorize at all optimization levels greater than 1 except for -Oz.
 /// For -Oz the loop vectorizer is disable, while the slp vectorizer is enabled.
 static bool shouldEnableVectorizerAtOLevel(const ArgList &Args, bool isSlpVec) {
@@ -3800,14 +3812,7 @@
   // Add in -fdebug-compilation-dir if necessary.
   addDebugCompDirArg(Args, CmdArgs);
 
-  for (const Arg *A : Args.filtered(options::OPT_fdebug_prefix_map_EQ)) {
-    StringRef Map = A->getValue();
-    if (Map.find('=') == StringRef::npos)
-      D.Diag(diag::err_drv_invalid_argument_to_fdebug_prefix_map) << Map;
-    else
-      CmdArgs.push_back(Args.MakeArgString("-fdebug-prefix-map=" + Map));
-    A->claim();
-  }
+  addDebugPrefixMapArg(D, Args, CmdArgs);
 
   if (Arg *A = Args.getLastArg(options::OPT_ftemplate_depth_,
                                options::OPT_ftemplate_depth_EQ)) {
@@ -5352,6 +5357,8 @@
     // Add the -fdebug-compilation-dir flag if needed.
     addDebugCompDirArg(Args, CmdArgs);
 
+    addDebugPrefixMapArg(getToolChain().getDriver(), Args, CmdArgs);
+
     // Set the AT_producer to the clang version when using the integrated
     // assembler on assembly source files.
     CmdArgs.push_back("-dwarf-debug-producer");
Index: test/Driver/debug-prefix-map.S
===================================================================
--- test/Driver/debug-prefix-map.S
+++ test/Driver/debug-prefix-map.S
@@ -0,0 +1,6 @@
+// RUN: %clang -### -g -fdebug-prefix-map=old=new %s 2>&1 | FileCheck %s
+
+// CHECK: cc1as
+// CHECK-SAME: -fdebug-prefix-map=old=new
+
+// More tests for this flag in debug-prefix-map.c.
Index: tools/driver/cc1as_main.cpp
===================================================================
--- tools/driver/cc1as_main.cpp
+++ tools/driver/cc1as_main.cpp
@@ -94,6 +94,7 @@
   std::string DwarfDebugFlags;
   std::string DwarfDebugProducer;
   std::string DebugCompilationDir;
+  std::map<const std::string, const std::string> DebugPrefixMap;
   llvm::DebugCompressionType CompressDebugSections =
       llvm::DebugCompressionType::None;
   std::string MainFileName;
@@ -233,6 +234,9 @@
   Opts.DebugCompilationDir = Args.getLastArgValue(OPT_fdebug_compilation_dir);
   Opts.MainFileName = Args.getLastArgValue(OPT_main_file_name);
 
+  for (const auto &Arg : Args.getAllArgValues(OPT_fdebug_prefix_map_EQ))
+    Opts.DebugPrefixMap.insert(StringRef(Arg).split('='));
+
   // Frontend Options
   if (Args.hasArg(OPT_INPUT)) {
     bool First = true;
@@ -377,6 +381,9 @@
     Ctx.setDwarfDebugProducer(StringRef(Opts.DwarfDebugProducer));
   if (!Opts.DebugCompilationDir.empty())
     Ctx.setCompilationDir(Opts.DebugCompilationDir);
+  if (!Opts.DebugPrefixMap.empty())
+    for (const auto &KV : Opts.DebugPrefixMap)
+      Ctx.addDebugPrefixMapEntry(KV.first, KV.second);
   if (!Opts.MainFileName.empty())
     Ctx.setMainFileName(StringRef(Opts.MainFileName));
   Ctx.setDwarfVersion(Opts.DwarfVersion);