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

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+62326862>

https://reviews.llvm.org/D79273

lldb/include/lldb/Core/Module.h

@@ -512,7 +512,6 @@ public:
 
   /// 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);
 
@@ -864,11 +863,6 @@ public:
   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);
 
@@ -984,9 +978,6 @@ protected:
   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

@@ -18,6 +18,7 @@
 #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"
@@ -128,6 +129,8 @@ public:
   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

@@ -1598,9 +1598,6 @@ bool Module::RemapSourceFile(llvm::StringRef path,
 
 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.cpp

@@ -664,12 +664,6 @@ lldb::CompUnitSP SymbolFileDWARF::ParseCompileUnit(DWARFCompileUnit &dwarf_cu) {
         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);
 
@@ -778,6 +772,26 @@ lldb::LanguageType SymbolFileDWARF::ParseLanguage(CompileUnit &comp_unit) {
     return eLanguageTypeUnknown;
 }
 
+XcodeSDK SymbolFileDWARF::ParseXcodeSDK(CompileUnit &comp_unit) {
+  std::lock_guard<std::recursive_mutex> guard(GetModuleMutex());
+  DWARFUnit *dwarf_cu = GetDWARFCompileUnit(&comp_unit);
+  if (!dwarf_cu)
+    return {};
+  ModuleSP module_sp = m_objfile_sp->GetModule();
+  if (!module_sp)
+    return {};
+  const DWARFBaseDIE cu_die = dwarf_cu->GetNonSkeletonUnit().GetUnitDIEOnly();
+  if (!cu_die)
+    return {};
+  const char *sdk = cu_die.GetAttributeValueAsString(DW_AT_APPLE_sdk, nullptr);
+  if (!sdk)
+    return {};
+  const char *sysroot =
+      cu_die.GetAttributeValueAsString(DW_AT_LLVM_sysroot, "");
+  module_sp->RegisterXcodeSDK(sdk, sysroot);
+  return {sdk};
+}
+
 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/SymbolFileDWARF.h

@@ -106,6 +106,9 @@ public:
   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

@@ -628,6 +628,15 @@ SymbolFileDWARFDebugMap::ParseLanguage(CompileUnit &comp_unit) {
   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/source/Plugins/SymbolFile/DWARF/SymbolFileDWARFDebugMap.h

@@ -58,6 +58,9 @@ public:
   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/unittests/SymbolFile/DWARF/XcodeSDKModuleTests.cpp

@@ -64,13 +64,13 @@ debug_info:
 
   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