Index: clang/include/clang/Driver/CC1Options.td
===================================================================
--- clang/include/clang/Driver/CC1Options.td
+++ clang/include/clang/Driver/CC1Options.td
@@ -687,7 +687,7 @@
 def version : Flag<["-"], "version">,
   HelpText<"Print the compiler version">;
 def main_file_name : Separate<["-"], "main-file-name">,
-  HelpText<"Main file name to use for debug info">;
+  HelpText<"Main file name to use for debug info and source if missing">;
 def split_dwarf_output : Separate<["-"], "split-dwarf-output">,
   HelpText<"File name to use for split dwarf debug info output">;
 
Index: clang/lib/Frontend/FrontendAction.cpp
===================================================================
--- clang/lib/Frontend/FrontendAction.cpp
+++ clang/lib/Frontend/FrontendAction.cpp
@@ -819,6 +819,10 @@
     std::string PresumedInputFile = getCurrentFileOrBufferName();
     if (Input.isPreprocessed())
       ReadOriginalFileName(CI, PresumedInputFile);
+    else if (PresumedInputFile == "-" &&
+             !CI.getCodeGenOpts().MainFileName.empty()) {
+      PresumedInputFile = CI.getCodeGenOpts().MainFileName;
+    }
 
     std::unique_ptr<ASTConsumer> Consumer =
         CreateWrappedASTConsumer(CI, PresumedInputFile);
Index: clang/test/Frontend/stdin-input
===================================================================
--- /dev/null
+++ clang/test/Frontend/stdin-input
@@ -0,0 +1,7 @@
+// RUN: cat %s | %clang -emit-llvm -g -S \
+// RUN: -Xclang -main-file-name -Xclang test/foo.c -x c - -o - | FileCheck %s
+// CHECK: ; ModuleID = 'test/foo.c'
+// CHECK: source_filename = "test/foo.c"
+// CHECK: !1 = !DIFile(filename: "test/foo.c"
+
+int main() {}
\ No newline at end of file