DWARF: Add "dwo_num" field to the DIERef class

Summary:
When dwo support was introduced, it used a trick where debug info
entries were referenced by the offset of the compile unit in the main
file, but the die offset was relative to the dwo file. Although there
was some elegance to it, this representation was starting to reach its
breaking point:
- the fact that the skeleton compile unit owned the DWO file meant that
  it was impossible (or at least hard and unintuitive) to support DWO
  files containing more than one compile unit. These kinds of files are
  produced by LTO for example.
- it made it impossible to reference any DIEs in the skeleton compile
  unit (although the skeleton units are generally empty, clang still
  puts some info into them with -fsplit-dwarf-inlining).
- (current motivation) it made it very hard to support type units placed
  in DWO files, as type units don't have any skeleton units which could
  be referenced in the main file

This patch addresses this problem by introducing an new
"dwo_num" field to the DIERef class, whose purpose is to identify the
dwo file. It's kind of similar to the dwo_id field in DWARF5 unit
headers, but while this is a 64bit hash whose main purpose is to catch
file mismatches, this is just a smaller integer used to indentify a
loaded dwo file. Currently, this is based on the index of the skeleton
compile unit which owns the dwo file, but it is intended to be
eventually independent of that (to support the LTO use case).

Simultaneously the cu_offset is dropped to conserve space, as it is no
longer necessary.  This means we can remove the "BaseObjectOffset" field
from the DWARFUnit class. It also means we can remove some of the
workarounds put in place to support the skeleton-unit+dwo-die combo.
More work is needed to remove all of them, which is out of scope of this
patch.

Reviewers: JDevlieghere, clayborg, aprantl

Subscribers: mehdi_amini, dexonsmith, arphaman, lldb-commits

Differential Revision: https://reviews.llvm.org/D63428

llvm-svn: 364009

1 files changed, 29 insertions, 20 deletions

diff --git a/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp b/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
index cb8ab15ea14..e2ddcfc5d64 100644
--- a/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
+++ b/lldb/source/Plugins/SymbolFile/DWARF/SymbolFileDWARF.cpp
@@ -1199,6 +1199,15 @@ void SymbolFileDWARF::ParseDeclsForContext(CompilerDeclContext decl_ctx) {
       ast_parser->GetDeclForUIDFromDWARF(decl);
 }
 
+user_id_t SymbolFileDWARF::GetUID(DIERef ref) {
+  if (GetDebugMapSymfile())
+    return GetID() | ref.die_offset();
+
+  return user_id_t(GetDwoNum().getValueOr(0x7fffffff)) << 32 |
+         ref.die_offset() |
+         (lldb::user_id_t(ref.section() == DIERef::Section::DebugTypes) << 63);
+}
+
 llvm::Optional<SymbolFileDWARF::DecodedUID>
 SymbolFileDWARF::DecodeUID(lldb::user_id_t uid) {
   // This method can be called without going through the symbol vendor so we
@@ -1215,25 +1224,20 @@ SymbolFileDWARF::DecodeUID(lldb::user_id_t uid) {
     SymbolFileDWARF *dwarf = debug_map->GetSymbolFileByOSOIndex(
         debug_map->GetOSOIndexFromUserID(uid));
     return DecodedUID{
-        *dwarf,
-        {DIERef::Section::DebugInfo, DW_INVALID_OFFSET, dw_offset_t(uid)}};
+        *dwarf, {llvm::None, DIERef::Section::DebugInfo, dw_offset_t(uid)}};
   }
-  DIERef::Section section =
-      uid >> 63 ? DIERef::Section::DebugTypes : DIERef::Section::DebugInfo;
-  uint32_t dwarf_id = uid >> 32 & 0x7fffffff;
   dw_offset_t die_offset = uid;
-
   if (die_offset == DW_INVALID_OFFSET)
     return llvm::None;
 
-  SymbolFileDWARF *dwarf = this;
-  if (DebugInfo()) {
-    if (DWARFUnit *unit = DebugInfo()->GetUnitAtIndex(dwarf_id)) {
-      if (unit->GetDwoSymbolFile())
-        dwarf = unit->GetDwoSymbolFile();
-    }
-  }
-  return DecodedUID{*dwarf, {section, DW_INVALID_OFFSET, die_offset}};
+  DIERef::Section section =
+      uid >> 63 ? DIERef::Section::DebugTypes : DIERef::Section::DebugInfo;
+
+  llvm::Optional<uint32_t> dwo_num = uid >> 32 & 0x7fffffff;
+  if (*dwo_num == 0x7fffffff)
+    dwo_num = llvm::None;
+
+  return DecodedUID{*this, {dwo_num, section, die_offset}};
 }
 
 DWARFDIE
@@ -1493,6 +1497,14 @@ lldb::ModuleSP SymbolFileDWARF::GetDWOModule(ConstString name) {
 
 DWARFDIE
 SymbolFileDWARF::GetDIE(const DIERef &die_ref) {
+  if (die_ref.dwo_num()) {
+    return DebugInfo()
+        ->GetUnitAtIndex(*die_ref.dwo_num())
+        ->GetDwoSymbolFile()
+        ->GetDIE(die_ref);
+  }
+
+
   DWARFDebugInfo *debug_info = DebugInfo();
   if (debug_info)
     return debug_info->GetDIE(die_ref);
@@ -2235,10 +2247,6 @@ uint32_t SymbolFileDWARF::FindFunctions(
 
   const uint32_t original_size = sc_list.GetSize();
 
-  DWARFDebugInfo *info = DebugInfo();
-  if (info == nullptr)
-    return 0;
-
   llvm::DenseSet<const DWARFDebugInfoEntry *> resolved_dies;
   DIEArray offsets;
   CompilerDeclContext empty_decl_ctx;
@@ -2246,7 +2254,7 @@ uint32_t SymbolFileDWARF::FindFunctions(
     parent_decl_ctx = &empty_decl_ctx;
 
   std::vector<DWARFDIE> dies;
-  m_index->GetFunctions(name, *info, *parent_decl_ctx, name_type_mask, dies);
+  m_index->GetFunctions(name, *this, *parent_decl_ctx, name_type_mask, dies);
   for (const DWARFDIE &die: dies) {
     if (resolved_dies.insert(die.GetDIE()).second)
       ResolveFunction(die, include_inlines, sc_list);
@@ -3081,7 +3089,8 @@ size_t SymbolFileDWARF::ParseVariablesForContext(const SymbolContext &sc) {
         sc.comp_unit->SetVariableList(variables);
 
         DIEArray die_offsets;
-        m_index->GetGlobalVariables(*dwarf_cu, die_offsets);
+        m_index->GetGlobalVariables(dwarf_cu->GetNonSkeletonUnit(),
+                                    die_offsets);
         const size_t num_matches = die_offsets.size();
         if (num_matches) {
           for (size_t i = 0; i < num_matches; ++i) {