Add an explicit API to read the Xcode SDK DWARF attribute from compile units

[aprantl]

Summary

When debugging from a SymbolMap the creation of CompileUnits for the
individual object files is so lazy that RegisterXcodeSDK() is not invoked at all
before the Swift TypeSystem wants to read it. This patch fixes this by
introducing an explicit SymbolFile::ParseXcodeSDK() call that can be
invoked deterministically before the result is required.

rdar://problem/62532151

[aprantl]

Delete more code that is made obsolete by the new API.

[aprantl]

ping.

[friss]

This looks good to me. If a similar API made sense on Module, I guess it can live on SymboleFile.

[teemperor]

lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp

786

I think we can early-exit here?

[aprantl]

This comment was removed by aprantl.

[aprantl]

Updated the wrong review...

[aprantl]

5935227e11f5b8e7111ee4a076c10a62d0648689

lldb/include/lldb/Core/Module.h

 
   /// This callback will be called by SymbolFile implementations when
   /// parsing a compile unit that contains SDK information.
-  /// \param sdk will be merged with \p m_sdk.
   /// \param sysroot will be added to the path remapping dictionary.
   void RegisterXcodeSDK(llvm::StringRef sdk, llvm::StringRef sysroot);
 

   bool RemapSourceFile(llvm::StringRef path, std::string &new_path) const;
   bool RemapSourceFile(const char *, std::string &) const = delete;
 
-  /// Return the Xcode SDK this module was compiled against.  This
-  /// is computed by merging the SDKs from each compilation unit in
-  /// the module.
-  XcodeSDK GetXcodeSDK() const { return m_xcode_sdk; }
-
   /// Update the ArchSpec to a more specific variant.
   bool MergeArchitecture(const ArchSpec &arch_spec);
 

   PathMappingList m_source_mappings =
       ModuleList::GetGlobalModuleListProperties().GetSymlinkMappings();
 
-  /// The (Xcode) SDK this module was compiled with.
-  XcodeSDK m_xcode_sdk;
-  
   lldb::SectionListUP m_sections_up; ///< Unified section list for module that
                                      /// is used by the ObjectFile and and
                                      /// ObjectFile instances for the debug info

lldb/include/lldb/Symbol/SymbolFile.h

 #include "lldb/Symbol/Type.h"
 #include "lldb/Symbol/TypeList.h"
 #include "lldb/Symbol/TypeSystem.h"
+#include "lldb/Utility/XcodeSDK.h"
 #include "lldb/lldb-private.h"
 #include "llvm/ADT/DenseSet.h"
 #include "llvm/Support/Errc.h"

   Symtab *GetSymtab();
 
   virtual lldb::LanguageType ParseLanguage(CompileUnit &comp_unit) = 0;
+  /// Return the Xcode SDK comp_unit was compiled against.
+  virtual XcodeSDK ParseXcodeSDK(CompileUnit &comp_unit) { return {}; }
   virtual size_t ParseFunctions(CompileUnit &comp_unit) = 0;
   virtual bool ParseLineTable(CompileUnit &comp_unit) = 0;
   virtual bool ParseDebugMacros(CompileUnit &comp_unit) = 0;

lldb/source/Core/Module.cpp

 
 void Module::RegisterXcodeSDK(llvm::StringRef sdk_name, llvm::StringRef sysroot) {
   XcodeSDK sdk(sdk_name.str());
-  if (m_xcode_sdk == sdk)
-    return;
-  m_xcode_sdk.Merge(sdk);
   PlatformSP module_platform =
       Platform::GetPlatformForArchitecture(GetArchitecture(), nullptr);
   ConstString sdk_path(module_platform->GetSDKPath(sdk));

lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.h

   lldb::LanguageType
   ParseLanguage(lldb_private::CompileUnit &comp_unit) override;
 
+  lldb_private::XcodeSDK
+  ParseXcodeSDK(lldb_private::CompileUnit &comp_unit) override;
+
   size_t ParseFunctions(lldb_private::CompileUnit &comp_unit) override;
 
   bool ParseLineTable(lldb_private::CompileUnit &comp_unit) override;

lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp

         const DWARFBaseDIE cu_die =
             dwarf_cu.GetNonSkeletonUnit().GetUnitDIEOnly();
         if (cu_die) {
-          if (const char *sdk =
-                  cu_die.GetAttributeValueAsString(DW_AT_APPLE_sdk, nullptr)) {
-            const char *sysroot =
-                cu_die.GetAttributeValueAsString(DW_AT_LLVM_sysroot, "");
-            module_sp->RegisterXcodeSDK(sdk, sysroot);
-          }
           FileSpec cu_file_spec(cu_die.GetName(), dwarf_cu.GetPathStyle());
           MakeAbsoluteAndRemap(cu_file_spec, dwarf_cu, module_sp);
 

     return eLanguageTypeUnknown;
 }
 
+XcodeSDK SymbolFileDWARF::ParseXcodeSDK(CompileUnit &comp_unit) {
+  std::lock_guard<std::recursive_mutex> guard(GetModuleMutex());
+  if (DWARFUnit *dwarf_cu = GetDWARFCompileUnit(&comp_unit))
+    if (ModuleSP module_sp = m_objfile_sp->GetModule())
+      if (const DWARFBaseDIE cu_die =
+              dwarf_cu->GetNonSkeletonUnit().GetUnitDIEOnly())
+        if (const char *sdk =
+                cu_die.GetAttributeValueAsString(DW_AT_APPLE_sdk, nullptr)) {
+          const char *sysroot =
+              cu_die.GetAttributeValueAsString(DW_AT_LLVM_sysroot, "");
+          module_sp->RegisterXcodeSDK(sdk, sysroot);
+          return {sdk};
+        }
+  return {};
+}
+
 size_t SymbolFileDWARF::ParseFunctions(CompileUnit &comp_unit) {
   static Timer::Category func_cat(LLVM_PRETTY_FUNCTION);
   Timer scoped_timer(func_cat, "SymbolFileDWARF::ParseFunctions");

lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARFDebugMap.h

   lldb::LanguageType
   ParseLanguage(lldb_private::CompileUnit &comp_unit) override;
 
+  lldb_private::XcodeSDK
+  ParseXcodeSDK(lldb_private::CompileUnit &comp_unit) override;
+
   size_t ParseFunctions(lldb_private::CompileUnit &comp_unit) override;
 
   bool ParseLineTable(lldb_private::CompileUnit &comp_unit) override;

lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARFDebugMap.cpp

   return eLanguageTypeUnknown;
 }
 
+XcodeSDK
+SymbolFileDWARFDebugMap::ParseXcodeSDK(CompileUnit &comp_unit) {
+  std::lock_guard<std::recursive_mutex> guard(GetModuleMutex());
+  SymbolFileDWARF *oso_dwarf = GetSymbolFile(comp_unit);
+  if (oso_dwarf)
+    return oso_dwarf->ParseXcodeSDK(comp_unit);
+  return {};
+}
+
 size_t SymbolFileDWARFDebugMap::ParseFunctions(CompileUnit &comp_unit) {
   std::lock_guard<std::recursive_mutex> guard(GetModuleMutex());
   SymbolFileDWARF *oso_dwarf = GetSymbolFile(comp_unit);

lldb/unittests/SymbolFile/DWARF/XcodeSDKModuleTests.cpp

 
   auto triple = "x86_64-apple-macosx";
   YAMLModuleTester t(yamldata, triple);
-  auto module = t.GetModule();
   auto dwarf_unit_sp = t.GetDwarfUnit();
   auto *dwarf_cu = llvm::cast<DWARFCompileUnit>(dwarf_unit_sp.get());
   ASSERT_TRUE((bool)dwarf_cu);
-  ASSERT_TRUE((bool)dwarf_cu->GetSymbolFileDWARF().GetCompUnitForDWARFCompUnit(
-      *dwarf_cu));
-  XcodeSDK sdk = module->GetXcodeSDK();
+  SymbolFileDWARF &sym_file = dwarf_cu->GetSymbolFileDWARF();
+  CompUnitSP comp_unit = sym_file.GetCompileUnitAtIndex(0);
+  ASSERT_TRUE((bool)comp_unit.get());
+  XcodeSDK sdk = sym_file.ParseXcodeSDK(*comp_unit);
   ASSERT_EQ(sdk.GetType(), XcodeSDK::Type::MacOSX);
 }
 #endif