Correctly initialize the DW_AT_comp_dir attribute of Clang module skeleton CUs

[aprantl]

Summary

Before this patch a Clang module skeleton CU would have a DW_AT_comp_dir pointing to the directory of the module map file, and this information was not used by anyone. Even worse, LLDB actually resolves relative DWO paths by appending it to DW_AT_comp_dir. This patch sets it to the same directory that is used as the main CU's compilation directory, which would make the LLDB code work.

[probinson]

clang/lib/CodeGen/CGDebugInfo.cpp

2499

The isOptimized parameter changed from true to false?

[aprantl]

clang/lib/CodeGen/CGDebugInfo.cpp

2499

Good catch, that was a drive-by fix. It has no meaning in the skeleton CU so we might as well not set it. Should be a separate commit though.

clang/lib/CodeGen/CGDebugInfo.cpp

     // 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());
-    DIB.createCompileUnit(TheCU->getSourceLanguage(),
-                          // TODO: Support "Source" from external AST providers?
-                          DIB.createFile(Mod.getModuleName(), Mod.getPath()),
-                          TheCU->getProducer(), true, StringRef(), 0,
-                          Mod.getASTFile(), llvm::DICompileUnit::FullDebug,
-                          Signature);
+    DIB.createCompileUnit(
+        TheCU->getSourceLanguage(),
+        // TODO: Support "Source" from external AST providers?
+        DIB.createFile(Mod.getModuleName(), TheCU->getDirectory()),
+        TheCU->getProducer(), false, StringRef(), 0, Mod.getASTFile(),
+        llvm::DICompileUnit::FullDebug, Signature);
     DIB.finalize();
   }
 
   llvm::DIModule *Parent =
       IsRootModule ? nullptr
                    : getOrCreateModuleRef(ASTSourceDescriptor(*M->Parent),
                                           CreateSkeletonCU);
   llvm::DIModule *DIMod =

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

 // RUN:     | 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 -fmodules-cache-path=%t \
 // 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: distinct !DICompileUnit
-// SKEL-CHECK: distinct !DICompileUnit{{.*}}dwoId
+// SKEL-CHECK: distinct !DICompileUnit({{.*}}file: ![[CUFILE:[0-9]+]]
+// SKEL-CHECK: ![[CUFILE]] = !DIFile({{.*}}directory: "[[COMP_DIR:.*]]"
+// SKEL-CHECK: distinct !DICompileUnit({{.*}}file: ![[DWOFILE:[0-9]+]]{{.*}}dwoId
+// SKEL-CHECK: ![[DWOFILE]] = !DIFile({{.*}}directory: "[[COMP_DIR]]"