Allow remapping Clang module include paths

[aprantl]

Summary

rdar://problem/55685132

[aprantl]

clang/lib/CodeGen/CGDebugInfo.cpp

2488

Is this legal?

remapDIPath takes a StringRef to Path. Is the sret value going to be a temporary or are we modifying the contents of the string while reading from it in remapDIPath?

[JDevlieghere]

clang/lib/CodeGen/CGDebugInfo.cpp

2488

No, this returns a std::string so you're returning a StringRef to a stack-allocated temporary. The lambda should return a std::string too.

[aprantl]

Don't try to be too clever.

[shafik]

clang/lib/CodeGen/CGDebugInfo.cpp

2487

& -> &TheCU

We should try to explicitly capture what we use, this will avoid potential bugs where we accidentally modify something we did not mean to capture later on when modifying the code.

[aprantl]

Rebased and addressed review comments.

[aprantl]

I had to revert this because it unexpectedly broke the "expr -- @import Module" test in LLDB.

[aprantl]

I'll update this with either a fix in clang or a patch to lldb once I figured out what happened.

http://green.lab.llvm.org/green/view/LLDB/job/lldb-cmake/13054/testReport/junit/lldb-api/lang_cpp_modules-import/TestCXXModulesImport_py/

[aprantl]

LLDB didn't apply DW_AT_comp_dir to DW_AT_LLVM_include_path. I fixed that now.

clang/lib/CodeGen/CGDebugInfo.cpp

   bool IsRootModule = M ? !M->Parent : true;
   // When a module name is specified as -fmodule-name, that module gets a
   // clang::Module object, but it won't actually be built or imported; it will
   // be textual.
   if (CreateSkeletonCU && IsRootModule && Mod.getASTFile().empty() && M)
     assert(StringRef(M->Name).startswith(CGM.getLangOpts().ModuleName) &&
            "clang module without ASTFile must be specified by -fmodule-name");
 
+  // Return a StringRef to the remapped Path. Modifies the input!
+  auto RemapPath = [&](std::string &Path) {
+    Path = remapDIPath(Path);
+    StringRef Relative(Path);
+    Relative.consume_front(TheCU->getDirectory());
+    return Relative;
+  };
+
   if (CreateSkeletonCU && IsRootModule && !Mod.getASTFile().empty()) {
     // PCH files don't have a signature field in the control block,
     // but LLVM detects skeleton CUs by looking for a non-zero DWO id.
     // We use the lower 64 bits for debug info.
     uint64_t Signature =
         Mod.getSignature()
             ? (uint64_t)Mod.getSignature()[1] << 32 | Mod.getSignature()[0]
             : ~1ULL;
     llvm::DIBuilder DIB(CGM.getModule());
-    std::string PCM = remapDIPath(Mod.getASTFile());
-    StringRef RelativePCM(PCM);
-    RelativePCM.consume_front(TheCU->getDirectory());
+    std::string PCM = Mod.getASTFile().str();
     DIB.createCompileUnit(
         TheCU->getSourceLanguage(),
         // TODO: Support "Source" from external AST providers?
         DIB.createFile(Mod.getModuleName(), TheCU->getDirectory()),
-        TheCU->getProducer(), false, StringRef(), 0, RelativePCM,
+        TheCU->getProducer(), false, StringRef(), 0, RemapPath(PCM),
         llvm::DICompileUnit::FullDebug, Signature);
     DIB.finalize();
   }
 
   llvm::DIModule *Parent =
       IsRootModule ? nullptr
                    : getOrCreateModuleRef(ASTSourceDescriptor(*M->Parent),
                                           CreateSkeletonCU);
+  std::string IncludePath = Mod.getPath().str();
   llvm::DIModule *DIMod =
       DBuilder.createModule(Parent, Mod.getModuleName(), ConfigMacros,
-                            Mod.getPath());
+                            RemapPath(IncludePath));
   ModuleCache[M].reset(DIMod);
   return DIMod;
 }
 
 llvm::DIType *CGDebugInfo::CreateTypeDefinition(const ObjCInterfaceType *Ty,
                                                 llvm::DIFile *Unit) {
   ObjCInterfaceDecl *ID = Ty->getDecl();
   llvm::DIFile *DefUnit = getOrCreateFile(ID->getLocation());

clang/test/Modules/debug-info-moduleimport.m

 // RUN: %clang_cc1 -debug-info-kind=limited -fmodules -fimplicit-module-maps \
 // RUN:   -fmodules-cache-path=%t %s -I %S/Inputs -isysroot /tmp/.. -I %t \
 // RUN:   -emit-llvm -o - | FileCheck %s --check-prefix=NO-SKEL-CHECK
 // NO-SKEL-CHECK: distinct !DICompileUnit
 // NO-SKEL-CHECK-NOT: distinct !DICompileUnit
 
 // RUN: %clang_cc1 -debug-info-kind=limited -fmodules -fimplicit-module-maps \
 // RUN:   -fmodules-cache-path=%t -fdebug-prefix-map=%t=/MODULE-CACHE \
+// RUN:   -fdebug-prefix-map=%S=/SRCDIR \
 // RUN:   -fmodule-format=obj -dwarf-ext-refs \
 // RUN:   %s -I %S/Inputs -isysroot /tmp/.. -I %t -emit-llvm -o - \
 // RUN:     | FileCheck %s --check-prefix=SKEL-CHECK
+// SKEL-CHECK: includePath: "/SRCDIR/Inputs"
 // SKEL-CHECK: distinct !DICompileUnit({{.*}}file: ![[CUFILE:[0-9]+]]
 // SKEL-CHECK: ![[CUFILE]] = !DIFile({{.*}}directory: "[[COMP_DIR:.*]]"
 // SKEL-CHECK: distinct !DICompileUnit({{.*}}file: ![[DWOFILE:[0-9]+]]{{.*}}splitDebugFilename: "/MODULE-CACHE{{.*}}dwoId
 // SKEL-CHECK: ![[DWOFILE]] = !DIFile({{.*}}directory: "[[COMP_DIR]]"