DWARFContext: Return empty data extractors instead of null pointers

Summary:
There are several reasons for doing this:
- generally, there's no reason to differentiate between a section being
  absent and it being present, but empty
- it matches more closely what llvm DWARF parser is doing (which also
  doesn't differentiate the two cases)
- SymbolFileDWARF also doesn't differentiate the two cases, which makes
  porting the rest of sections easier
- it fixes a bug in how the return-null-if-empty logic was implemented
  (it returned nullptr only the second time we tried to get the
  debug_aranges section), which meant that we hit an assert when trying
  to parse an empty-but-present section

Reviewers: JDevlieghere, clayborg, aprantl

Subscribers: zturner, lldb-commits

Differential Revision: https://reviews.llvm.org/D61942

llvm-svn: 360874

4 files changed, 23 insertions, 27 deletions

diff --git a/lldb/source/Plugins/SymbolFile/DWARF/DWARFContext.cpp b/lldb/source/Plugins/SymbolFile/DWARF/DWARFContext.cpp
index d8a44ccacb9..aba2979383d 100644
--- a/lldb/source/Plugins/SymbolFile/DWARF/DWARFContext.cpp
+++ b/lldb/source/Plugins/SymbolFile/DWARF/DWARFContext.cpp
@@ -13,31 +13,32 @@
 using namespace lldb;
 using namespace lldb_private;
 
-static const DWARFDataExtractor *
-LoadOrGetSection(Module &module, SectionType section_type,
-                 llvm::Optional<DWARFDataExtractor> &extractor) {
-  if (extractor.hasValue())
-    return extractor->GetByteSize() > 0 ? extractor.getPointer() : nullptr;
-
-  // Initialize to an empty extractor so that we always take the fast path going
-  // forward.
-  extractor.emplace();
-
-  const SectionList *section_list = module.GetSectionList();
+static DWARFDataExtractor LoadSection(Module &module,
+                                      SectionType section_type) {
+  SectionList *section_list = module.GetSectionList();
   if (!section_list)
-    return nullptr;
+    return DWARFDataExtractor();
 
   auto section_sp = section_list->FindSectionByType(section_type, true);
   if (!section_sp)
-    return nullptr;
+    return DWARFDataExtractor();
 
-  section_sp->GetSectionData(*extractor);
-  return extractor.getPointer();
+  DWARFDataExtractor data;
+  section_sp->GetSectionData(data);
+  return data;
+}
+
+static const DWARFDataExtractor &
+LoadOrGetSection(Module &module, SectionType section_type,
+                 llvm::Optional<DWARFDataExtractor> &extractor) {
+  if (!extractor)
+    extractor = LoadSection(module, section_type);
+  return *extractor;
 }
 
 DWARFContext::DWARFContext(Module &module) : m_module(module) {}
 
-const DWARFDataExtractor *DWARFContext::getOrLoadArangesData() {
+const DWARFDataExtractor &DWARFContext::getOrLoadArangesData() {
   return LoadOrGetSection(m_module, eSectionTypeDWARFDebugAranges,
                           m_data_debug_aranges);
 }
diff --git a/lldb/source/Plugins/SymbolFile/DWARF/DWARFContext.h b/lldb/source/Plugins/SymbolFile/DWARF/DWARFContext.h
index 02887838705..4059d048aaf 100644
--- a/lldb/source/Plugins/SymbolFile/DWARF/DWARFContext.h
+++ b/lldb/source/Plugins/SymbolFile/DWARF/DWARFContext.h
@@ -23,7 +23,7 @@ private:
 public:
   explicit DWARFContext(Module &module);
 
-  const DWARFDataExtractor *getOrLoadArangesData();
+  const DWARFDataExtractor &getOrLoadArangesData();
 };
 } // namespace lldb_private
 
diff --git a/lldb/source/Plugins/SymbolFile/DWARF/DWARFDebugAranges.cpp b/lldb/source/Plugins/SymbolFile/DWARF/DWARFDebugAranges.cpp
index fcacf59d8b8..4d22c825390 100644
--- a/lldb/source/Plugins/SymbolFile/DWARF/DWARFDebugAranges.cpp
+++ b/lldb/source/Plugins/SymbolFile/DWARF/DWARFDebugAranges.cpp
@@ -42,8 +42,6 @@ public:
 // Extract
 llvm::Error
 DWARFDebugAranges::extract(const DWARFDataExtractor &debug_aranges_data) {
-  assert(debug_aranges_data.ValidOffset(0));
-
   lldb::offset_t offset = 0;
 
   DWARFDebugArangeSet set;
@@ -65,8 +63,8 @@ DWARFDebugAranges::extract(const DWARFDataExtractor &debug_aranges_data) {
       }
     }
     set.Clear();
-    }
-    return llvm::ErrorSuccess();
+  }
+  return llvm::ErrorSuccess();
 }
 
 void DWARFDebugAranges::Dump(Log *log) const {
diff --git a/lldb/source/Plugins/SymbolFile/DWARF/DWARFDebugInfo.cpp b/lldb/source/Plugins/SymbolFile/DWARF/DWARFDebugInfo.cpp
index de4a48a2c06..0daf489f4d5 100644
--- a/lldb/source/Plugins/SymbolFile/DWARF/DWARFDebugInfo.cpp
+++ b/lldb/source/Plugins/SymbolFile/DWARF/DWARFDebugInfo.cpp
@@ -44,13 +44,10 @@ llvm::Expected<DWARFDebugAranges &> DWARFDebugInfo::GetCompileUnitAranges() {
   assert(m_dwarf2Data);
 
   m_cu_aranges_up = llvm::make_unique<DWARFDebugAranges>();
-  const DWARFDataExtractor *debug_aranges_data =
+  const DWARFDataExtractor &debug_aranges_data =
       m_context.getOrLoadArangesData();
-  if (debug_aranges_data) {
-    llvm::Error error = m_cu_aranges_up->extract(*debug_aranges_data);
-    if (error)
-      return std::move(error);
-  }
+  if (llvm::Error error = m_cu_aranges_up->extract(debug_aranges_data))
+    return std::move(error);
 
   // Make a list of all CUs represented by the arange data in the file.
   std::set<dw_offset_t> cus_with_data;