[clang][DebugInfo] Respect fmodule-file-home-is-cwd in skeleton CUs for clang modules

[bulbazord]

Summary

When -fmodule-file-home-is-cwd and the path to the PCM is relative, we shouldn't assume that the path to the PCM is relative to the modulemap that produced it. To respect the option -fmodule-file-home-is-cwd, we should assume the path is relative to the current working directory.

[rmaz]

Nice, LGTM, thanks!

clang/lib/CodeGen/CGDebugInfo.cpp

if (CreateSkeletonCU && IsRootModule && !Mod.getASTFile().empty()) {
     uint64_t Signature = 0;
     if (const auto &ModSig = Mod.getSignature())
       Signature = ModSig.truncatedValue();
     else
       Signature = ~1ULL;
 
     llvm::DIBuilder DIB(CGM.getModule());
     SmallString<0> PCM;
-    if (!llvm::sys::path::is_absolute(Mod.getASTFile()))
+    if (!llvm::sys::path::is_absolute(Mod.getASTFile())) {
+      if (CGM.getHeaderSearchOpts().ModuleFileHomeIsCwd)
+        PCM = getCurrentDirname();
+      else
         PCM = Mod.getPath();
+    }
     llvm::sys::path::append(PCM, Mod.getASTFile());
     DIB.createCompileUnit(
         TheCU->getSourceLanguage(),
         // TODO: Support "Source" from external AST providers?
         DIB.createFile(Mod.getModuleName(), TheCU->getDirectory()),
         TheCU->getProducer(), false, StringRef(), 0, RemapPath(PCM),
         llvm::DICompileUnit::FullDebug, Signature);
     DIB.finalize();

clang/test/Modules/module-file-home-is-cwd.m

 // RUN: cd %S
-// RUN: %clang_cc1 -fmodules -fno-implicit-modules -fmodule-file-home-is-cwd -fmodule-name=libA -emit-module Inputs/normal-module-map/module.map -o %t/mod.pcm
+// RUN: %clang_cc1 -x objective-c -fmodules -fno-implicit-modules \
+// RUN:     -fmodule-file-home-is-cwd -fmodule-name=libA -emit-module \
+// RUN:     -fmodules-embed-all-files %S/Inputs/normal-module-map/module.map \
+// RUN:     -o %t/mod.pcm
 // RUN: llvm-bcanalyzer --dump --disable-histogram %t/mod.pcm | FileCheck %s
 
 // CHECK: <INPUT_FILE {{.*}}/> blob data = 'Inputs{{/|\\}}normal-module-map{{/|\\}}module.map'
 // CHECK: <INPUT_FILE {{.*}}/> blob data = 'Inputs{{/|\\}}normal-module-map{{/|\\}}a2.h'
 // CHECK: <INPUT_FILE {{.*}}/> blob data = 'Inputs{{/|\\}}normal-module-map{{/|\\}}a1.h'
 // CHECK-NOT: MODULE_DIRECTORY
+
+@import libA;
+
+// RUN: cd %t
+// RUN: %clang_cc1 -x objective-c -fmodules -fno-implicit-modules -debug-info-kind=limited \
+// RUN:     -debugger-tuning=lldb -dwarf-ext-refs -fmodule-file-home-is-cwd \
+// RUN:     -fmodule-map-file=%S/Inputs/normal-module-map/module.map \
+// RUN:     -fmodule-file=libA=mod.pcm -emit-llvm -o %t-mod.ll %s
+// RUN: cat %t-mod.ll | FileCheck %s --check-prefix=SKELETON
+
+// SKELETON: !DICompileUnit(language: DW_LANG_ObjC, {{.*}}, splitDebugFilename: "mod.pcm"