Add an option to disable DWARF skeleton CU breadcrumbs for Clang

include/swift/AST/IRGenOptions.h

@@ -104,14 +104,17 @@ class IRGenOptions {
   /// Which sanitizer is turned on.
   OptionSet<SanitizerKind> Sanitizers;
 
+  /// Path prefixes that should be rewritten in debug info.
+  PathRemapper DebugPrefixMap;
+
   /// What level of debug info to generate.
   IRGenDebugInfoLevel DebugInfoLevel : 2;
 
   /// What type of debug info to generate.
   IRGenDebugInfoFormat DebugInfoFormat : 2;
 
-  /// Path prefixes that should be rewritten in debug info.
-  PathRemapper DebugPrefixMap;
+  /// Whether to leave DWARF breadcrumbs pointing to imported Clang modules.
+  unsigned DisableClangModuleSkeletonCUs : 1;
 
   /// Whether we're generating IR for the JIT.
   unsigned UseJIT : 1;
@@ -227,7 +230,9 @@ class IRGenOptions {
         Verify(true), OptMode(OptimizationMode::NotSet),
         Sanitizers(OptionSet<SanitizerKind>()),
         DebugInfoLevel(IRGenDebugInfoLevel::None),
-        DebugInfoFormat(IRGenDebugInfoFormat::None), UseJIT(false),
+        DebugInfoFormat(IRGenDebugInfoFormat::None),
+        DisableClangModuleSkeletonCUs(false),
+        UseJIT(false),
         IntegratedREPL(false), DisableLLVMOptzns(false),
         DisableSwiftSpecificLLVMOptzns(false), DisableLLVMSLPVectorizer(false),
         DisableFPElim(true), Playground(false), EmitStackPromotionChecks(false),

include/swift/Option/FrontendOptions.td

@@ -432,6 +432,10 @@ def disable_playground_transform : Flag<["-"], "disable-playground-transform">,
 def pc_macro : Flag<["-"], "pc-macro">,
   HelpText<"Apply the 'program counter simulation' macro">;
 
+def no_clang_module_breadcrumbs : Flag<["-"], "no-clang-module-breadcrumbs">,
+  HelpText<"Don't emit DWARF skeleton CUs for imported Clang modules. "
+           "Use this when building a redistributable static archive.">;
+
 def use_jit : Flag<["-"], "use-jit">,
   HelpText<"Register Objective-C classes as if the JIT were in use">;
 

lib/Frontend/CompilerInvocation.cpp

@@ -1002,6 +1002,9 @@ static bool ParseIRGenArgs(IRGenOptions &Opts, ArgList &Args,
 
   Opts.ModuleName = FrontendOpts.ModuleName;
 
+  if (Args.hasArg(OPT_no_clang_module_breadcrumbs))
+    Opts.DisableClangModuleSkeletonCUs = true;
+
   if (Args.hasArg(OPT_use_jit))
     Opts.UseJIT = true;
 

lib/IRGen/IRGenDebugInfo.cpp

@@ -640,16 +640,19 @@ class IRGenDebugInfoImpl : public IRGenDebugInfo {
     std::string RemappedIncludePath = DebugPrefixMap.remapPath(IncludePath);
 
     // For Clang modules / PCH, create a Skeleton CU pointing to the PCM/PCH.
-    bool CreateSkeletonCU = !ASTFile.empty();
-    bool IsRootModule = !Parent;
-    if (CreateSkeletonCU && IsRootModule) {
-      llvm::DIBuilder DIB(M);
-      DIB.createCompileUnit(IGM.ObjCInterop ? llvm::dwarf::DW_LANG_ObjC
-                                            : llvm::dwarf::DW_LANG_C99,
-                            DIB.createFile(Name, RemappedIncludePath),
-                            TheCU->getProducer(), true, StringRef(), 0, ASTFile,
-                            llvm::DICompileUnit::FullDebug, Signature);
-      DIB.finalize();
+    if (!Opts.DisableClangModuleSkeletonCUs) {
+      bool CreateSkeletonCU = !ASTFile.empty();
+      bool IsRootModule = !Parent;
+      if (CreateSkeletonCU && IsRootModule) {
+        llvm::DIBuilder DIB(M);
+        DIB.createCompileUnit(IGM.ObjCInterop ? llvm::dwarf::DW_LANG_ObjC
+                                              : llvm::dwarf::DW_LANG_C99,
+                              DIB.createFile(Name, RemappedIncludePath),
+                              TheCU->getProducer(), true, StringRef(), 0,
+                              ASTFile, llvm::DICompileUnit::FullDebug,
+                              Signature);
+        DIB.finalize();
+      }
     }
 
     StringRef Sysroot = IGM.Context.SearchPathOpts.SDKPath;

test/DebugInfo/ClangModuleBreadcrumbs.swift

@@ -1,5 +1,9 @@
 // RUN: %target-swift-frontend -emit-ir %s -g -I %S/Inputs \
 // RUN:   -Xcc -DFOO="foo" -Xcc -UBAR -o - | %FileCheck %s
+//
+// RUN: %target-swift-frontend -emit-ir %s -g -I %S/Inputs \
+// RUN:   -Xcc -DFOO="foo" -Xcc -UBAR -o - -no-clang-module-breadcrumbs \
+// RUN:   | %FileCheck %s --check-prefix=NONE
 import ClangModule.SubModule
 import OtherClangModule.SubModule
 
@@ -11,3 +15,6 @@ import OtherClangModule.SubModule
 // CHECK: !DICompileUnit(language: DW_LANG_{{ObjC|C99}}, {{.*}} producer: "{{.*}}Swift
 // CHECK-SAME:           OtherClangModule
 // CHECK-SAME:           dwoId:
+
+// NONE: DICompileUnit({{.*}}
+// NONE-NOT: DICompileUnit({{.*}}ClangModule