Add a -debug-module-path frontend option

include/swift/AST/IRGenOptions.h

@@ -270,6 +270,9 @@ class IRGenOptions {
 public:
   std::string ModuleName;
 
+  /// The path to the main binary swiftmodule for the debug info.
+  std::string DebugModulePath;
+
   /// The compilation directory for the debug info.
   std::string DebugCompilationDir;
 

include/swift/Option/Options.td

@@ -643,6 +643,12 @@ def project_name : Separate<["-"], "project-name">,
 def module_name_EQ : Joined<["-"], "module-name=">, Flags<[FrontendOption]>,
   Alias<module_name>;
 
+def debug_module_path : Separate<["-"], "debug-module-path">,
+  Flags<[FrontendOption]>,
+  HelpText<"Path to this module's binary swiftmodule artifact (required by debug info)">;
+def debug_module_path_EQ : Joined<["-"], "debug-module-path=">, Flags<[FrontendOption]>,
+  Alias<debug_module_path>;
+
 def module_alias : Separate<["-"], "module-alias">,
   Flags<[FrontendOption, ModuleInterfaceOption]>,
   MetaVarName<"<alias_name=real_name>">,

lib/Frontend/CompilerInvocation.cpp

@@ -3460,6 +3460,9 @@ static bool ParseIRGenArgs(IRGenOptions &Opts, ArgList &Args,
                      A->getAsString(Args), A->getValue());
   }
 
+  if (const Arg *A = Args.getLastArg(options::OPT_debug_module_path))
+    Opts.DebugModulePath = A->getValue();
+
   for (auto A : Args.getAllArgValues(options::OPT_file_prefix_map)) {
     auto SplitMap = StringRef(A).split('=');
     Opts.FilePrefixMap.addMapping(SplitMap.first, SplitMap.second);

lib/IRGen/IRGenDebugInfo.cpp

@@ -864,7 +864,7 @@ class IRGenDebugInfoImpl : public IRGenDebugInfo {
   llvm::DIModule *getOrCreateModule(const void *Key, llvm::DIScope *Parent,
                                     StringRef Name, StringRef IncludePath,
                                     uint64_t Signature = ~1ULL,
-                                    StringRef ASTFile = StringRef()) {
+                                    StringRef ASTFile = {}) {
     // Look in the cache first.
     auto Val = DIModuleCache.find(Key);
     if (Val != DIModuleCache.end())
@@ -2823,8 +2823,12 @@ IRGenDebugInfoImpl::IRGenDebugInfoImpl(const IRGenOptions &Opts,
 
   // Create a module for the current compile unit.
   auto *MDecl = IGM.getSwiftModule();
-  llvm::sys::path::remove_filename(SourcePath);
-  MainModule = getOrCreateModule(MDecl, TheCU, Opts.ModuleName, SourcePath);
+  StringRef Path = Opts.DebugModulePath;
+  if (Path.empty()) {
+    llvm::sys::path::remove_filename(SourcePath);
+    Path = SourcePath;
+  }
+  MainModule = getOrCreateModule(MDecl, TheCU, Opts.ModuleName, Path);
   DBuilder.createImportedModule(MainFile, MainModule, MainFile, 0);
 
   // Macro definitions that were defined by the user with "-Xcc -D" on the

test/DebugInfo/ebm_module_path.swift

@@ -0,0 +1,4 @@
+// RUN: %target-swift-frontend -primary-file %s -emit-ir -g -module-name=A -debug-module-path %t/MY_MODULE_PATH.swiftmodule -emit-ir -o - | %FileCheck %s
+
+// CHECK: DIModule(scope: null, name: "A", includePath: "{{.*}}MY_MODULE_PATH.swiftmodule")
+