[lldb/DWARF] Refactor DWARFDIE::Get{Decl,TypeLookup}Context (#93291)

After a bug (the bug is that the functions don't handle DW_AT_signature,
aka type units) led me to one of these similar-but-different functions,
I started to realize that most of the differences between these two
functions are actually bugs.

As a first step towards merging them, this patch rewrites both of them
to follow the same pattern, while preserving all of their differences.
The main change is that GetTypeLookupContext now also uses a `seen` list
to avoid reference loops (currently that's not necessary because the
function strictly follows parent links, but that will change with
DW_AT_signatures).

I've also optimized both functions to avoid recursion by starting contruction
with the deepest scope first (and then reversing it).

4 files changed, 184 insertions, 93 deletions

diff --git a/lldb/include/lldb/Symbol/Type.h b/lldb/include/lldb/Symbol/Type.h
index 7aa0852..c6f30cd 100644
--- a/lldb/include/lldb/Symbol/Type.h
+++ b/lldb/include/lldb/Symbol/Type.h
@@ -62,6 +62,8 @@ struct CompilerContext {
   CompilerContextKind kind;
   ConstString name;
 };
+llvm::raw_ostream &operator<<(llvm::raw_ostream &os,
+                              const CompilerContext &rhs);
 
 /// Match \p context_chain against \p pattern, which may contain "Any"
 /// kinds. The \p context_chain should *not* contain any "Any" kinds.
diff --git a/lldb/source/Plugins/SymbolFile/DWARF/DWARFDIE.cpp b/lldb/source/Plugins/SymbolFile/DWARF/DWARFDIE.cpp
index 4884374..03e289b 100644
--- a/lldb/source/Plugins/SymbolFile/DWARF/DWARFDIE.cpp
+++ b/lldb/source/Plugins/SymbolFile/DWARF/DWARFDIE.cpp
@@ -13,6 +13,7 @@
 #include "DWARFDebugInfoEntry.h"
 #include "DWARFDeclContext.h"
 #include "DWARFUnit.h"
+#include "lldb/Symbol/Type.h"
 
 #include "llvm/ADT/iterator.h"
 
@@ -379,108 +380,118 @@ std::vector<DWARFDIE> DWARFDIE::GetDeclContextDIEs() const {
   return result;
 }
 
-static std::vector<lldb_private::CompilerContext>
-GetDeclContextImpl(llvm::SmallSet<lldb::user_id_t, 4> &seen, DWARFDIE die) {
-  std::vector<lldb_private::CompilerContext> context;
+static void GetDeclContextImpl(DWARFDIE die,
+                               llvm::SmallSet<lldb::user_id_t, 4> &seen,
+                               std::vector<CompilerContext> &context) {
   // Stop if we hit a cycle.
-  if (!die || !seen.insert(die.GetID()).second)
-    return context;
-
-  // Handle outline member function DIEs by following the specification.
-  if (DWARFDIE spec = die.GetReferencedDIE(DW_AT_specification))
-    return GetDeclContextImpl(seen, spec);
-
-  // Get the parent context chain.
-  context = GetDeclContextImpl(seen, die.GetParent());
+  while (die && seen.insert(die.GetID()).second) {
+    // Handle outline member function DIEs by following the specification.
+    if (DWARFDIE spec = die.GetReferencedDIE(DW_AT_specification)) {
+      die = spec;
+      continue;
+    }
 
-  // Add this DIE's contribution at the end of the chain.
-  auto push_ctx = [&](CompilerContextKind kind, llvm::StringRef name) {
-    context.push_back({kind, ConstString(name)});
-  };
-  switch (die.Tag()) {
-  case DW_TAG_module:
-    push_ctx(CompilerContextKind::Module, die.GetName());
-    break;
-  case DW_TAG_namespace:
-    push_ctx(CompilerContextKind::Namespace, die.GetName());
-    break;
-  case DW_TAG_structure_type:
-    push_ctx(CompilerContextKind::Struct, die.GetName());
-    break;
-  case DW_TAG_union_type:
-    push_ctx(CompilerContextKind::Union, die.GetName());
-    break;
-  case DW_TAG_class_type:
-    push_ctx(CompilerContextKind::Class, die.GetName());
-    break;
-  case DW_TAG_enumeration_type:
-    push_ctx(CompilerContextKind::Enum, die.GetName());
-    break;
-  case DW_TAG_subprogram:
-    push_ctx(CompilerContextKind::Function, die.GetName());
-    break;
-  case DW_TAG_variable:
-    push_ctx(CompilerContextKind::Variable, die.GetPubname());
-    break;
-  case DW_TAG_typedef:
-    push_ctx(CompilerContextKind::Typedef, die.GetName());
-    break;
-  default:
-    break;
+    // Add this DIE's contribution at the end of the chain.
+    auto push_ctx = [&](CompilerContextKind kind, llvm::StringRef name) {
+      context.push_back({kind, ConstString(name)});
+    };
+    switch (die.Tag()) {
+    case DW_TAG_module:
+      push_ctx(CompilerContextKind::Module, die.GetName());
+      break;
+    case DW_TAG_namespace:
+      push_ctx(CompilerContextKind::Namespace, die.GetName());
+      break;
+    case DW_TAG_structure_type:
+      push_ctx(CompilerContextKind::Struct, die.GetName());
+      break;
+    case DW_TAG_union_type:
+      push_ctx(CompilerContextKind::Union, die.GetName());
+      break;
+    case DW_TAG_class_type:
+      push_ctx(CompilerContextKind::Class, die.GetName());
+      break;
+    case DW_TAG_enumeration_type:
+      push_ctx(CompilerContextKind::Enum, die.GetName());
+      break;
+    case DW_TAG_subprogram:
+      push_ctx(CompilerContextKind::Function, die.GetName());
+      break;
+    case DW_TAG_variable:
+      push_ctx(CompilerContextKind::Variable, die.GetPubname());
+      break;
+    case DW_TAG_typedef:
+      push_ctx(CompilerContextKind::Typedef, die.GetName());
+      break;
+    default:
+      break;
+    }
+    // Now process the parent.
+    die = die.GetParent();
   }
-  return context;
 }
 
-std::vector<lldb_private::CompilerContext> DWARFDIE::GetDeclContext() const {
+std::vector<CompilerContext> DWARFDIE::GetDeclContext() const {
   llvm::SmallSet<lldb::user_id_t, 4> seen;
-  return GetDeclContextImpl(seen, *this);
+  std::vector<CompilerContext> context;
+  GetDeclContextImpl(*this, seen, context);
+  std::reverse(context.begin(), context.end());
+  return context;
 }
 
-std::vector<lldb_private::CompilerContext>
-DWARFDIE::GetTypeLookupContext() const {
-  std::vector<lldb_private::CompilerContext> context;
-  // If there is no name, then there is no need to look anything up for this
-  // DIE.
-  const char *name = GetName();
-  if (!name || !name[0])
-    return context;
-  const dw_tag_t tag = Tag();
-  if (tag == DW_TAG_compile_unit || tag == DW_TAG_partial_unit)
-    return context;
-  DWARFDIE parent = GetParent();
-  if (parent)
-    context = parent.GetTypeLookupContext();
-  auto push_ctx = [&](CompilerContextKind kind, llvm::StringRef name) {
-    context.push_back({kind, ConstString(name)});
-  };
-  switch (tag) {
-  case DW_TAG_namespace:
-    push_ctx(CompilerContextKind::Namespace, name);
-    break;
-  case DW_TAG_structure_type:
-    push_ctx(CompilerContextKind::Struct, name);
-    break;
-  case DW_TAG_union_type:
-    push_ctx(CompilerContextKind::Union, name);
-    break;
-  case DW_TAG_class_type:
-    push_ctx(CompilerContextKind::Class, name);
-    break;
-  case DW_TAG_enumeration_type:
-    push_ctx(CompilerContextKind::Enum, name);
-    break;
-  case DW_TAG_variable:
-    push_ctx(CompilerContextKind::Variable, GetPubname());
-    break;
-  case DW_TAG_typedef:
-    push_ctx(CompilerContextKind::Typedef, name);
-    break;
-  case DW_TAG_base_type:
-    push_ctx(CompilerContextKind::Builtin, name);
-    break;
-  default:
-    break;
+static void GetTypeLookupContextImpl(DWARFDIE die,
+                                     llvm::SmallSet<lldb::user_id_t, 4> &seen,
+                                     std::vector<CompilerContext> &context) {
+  // Stop if we hit a cycle.
+  while (die && seen.insert(die.GetID()).second) {
+    // If there is no name, then there is no need to look anything up for this
+    // DIE.
+    const char *name = die.GetName();
+    if (!name || !name[0])
+      return;
+
+    // Add this DIE's contribution at the end of the chain.
+    auto push_ctx = [&](CompilerContextKind kind, llvm::StringRef name) {
+      context.push_back({kind, ConstString(name)});
+    };
+    switch (die.Tag()) {
+    case DW_TAG_namespace:
+      push_ctx(CompilerContextKind::Namespace, die.GetName());
+      break;
+    case DW_TAG_structure_type:
+      push_ctx(CompilerContextKind::Struct, die.GetName());
+      break;
+    case DW_TAG_union_type:
+      push_ctx(CompilerContextKind::Union, die.GetName());
+      break;
+    case DW_TAG_class_type:
+      push_ctx(CompilerContextKind::Class, die.GetName());
+      break;
+    case DW_TAG_enumeration_type:
+      push_ctx(CompilerContextKind::Enum, die.GetName());
+      break;
+    case DW_TAG_variable:
+      push_ctx(CompilerContextKind::Variable, die.GetPubname());
+      break;
+    case DW_TAG_typedef:
+      push_ctx(CompilerContextKind::Typedef, die.GetName());
+      break;
+    case DW_TAG_base_type:
+      push_ctx(CompilerContextKind::Builtin, name);
+      break;
+    default:
+      break;
+    }
+    // Now process the parent.
+    die = die.GetParent();
   }
+}
+
+std::vector<CompilerContext> DWARFDIE::GetTypeLookupContext() const {
+  llvm::SmallSet<lldb::user_id_t, 4> seen;
+  std::vector<CompilerContext> context;
+  GetTypeLookupContextImpl(*this, seen, context);
+  std::reverse(context.begin(), context.end());
   return context;
 }
 
diff --git a/lldb/source/Symbol/Type.cpp b/lldb/source/Symbol/Type.cpp
index 6bf69c2..585808a 100644
--- a/lldb/source/Symbol/Type.cpp
+++ b/lldb/source/Symbol/Type.cpp
@@ -36,6 +36,13 @@
 using namespace lldb;
 using namespace lldb_private;
 
+llvm::raw_ostream &lldb_private::operator<<(llvm::raw_ostream &os,
+                                            const CompilerContext &rhs) {
+  StreamString lldb_stream;
+  rhs.Dump(lldb_stream);
+  return os << lldb_stream.GetString();
+}
+
 bool lldb_private::contextMatches(llvm::ArrayRef<CompilerContext> context_chain,
                                   llvm::ArrayRef<CompilerContext> pattern) {
   auto ctx = context_chain.begin();
diff --git a/lldb/unittests/SymbolFile/DWARF/DWARFDIETest.cpp b/lldb/unittests/SymbolFile/DWARF/DWARFDIETest.cpp
index 20742ea..bea07df 100644
--- a/lldb/unittests/SymbolFile/DWARF/DWARFDIETest.cpp
+++ b/lldb/unittests/SymbolFile/DWARF/DWARFDIETest.cpp
@@ -10,6 +10,8 @@
 #include "Plugins/SymbolFile/DWARF/DWARFDebugInfo.h"
 #include "TestingSupport/Symbol/YAMLModuleTester.h"
 #include "lldb/Core/dwarf.h"
+#include "lldb/Symbol/Type.h"
+#include "lldb/lldb-private-enumerations.h"
 #include "llvm/ADT/STLExtras.h"
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
@@ -187,3 +189,72 @@ DWARF:
   dw_offset_t fifth_die_offset = 26;
   EXPECT_EQ(unit->PeekDIEName(fifth_die_offset), "NameType2");
 }
+
+TEST(DWARFDIETest, GetContext) {
+  const char *yamldata = R"(
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_EXEC
+  Machine: EM_386
+DWARF:
+  debug_abbrev:
+    - ID:              0
+      Table:
+        - Code:            0x1
+          Tag:             DW_TAG_compile_unit
+          Children:        DW_CHILDREN_yes
+          Attributes:
+            - Attribute:       DW_AT_language
+              Form:            DW_FORM_data2
+        - Code:            0x2
+          Tag:             DW_TAG_namespace
+          Children:        DW_CHILDREN_yes
+          Attributes:
+            - Attribute:       DW_AT_name
+              Form:            DW_FORM_string
+        - Code:            0x3
+          Tag:             DW_TAG_structure_type
+          Children:        DW_CHILDREN_no
+          Attributes:
+            - Attribute:       DW_AT_name
+              Form:            DW_FORM_string
+  debug_info:
+    - Version:         4
+      AddrSize:        8
+      Entries:
+        - AbbrCode:        0x1
+          Values:
+            - Value:           0x000000000000000C
+        - AbbrCode:        0x2
+          Values:
+            - CStr:            NAMESPACE
+        - AbbrCode:        0x3
+          Values:
+            - CStr:            STRUCT
+        - AbbrCode:        0x0
+        - AbbrCode:        0x0
+)";
+
+  YAMLModuleTester t(yamldata);
+  auto *symbol_file =
+      llvm::cast<SymbolFileDWARF>(t.GetModule()->GetSymbolFile());
+  DWARFUnit *unit = symbol_file->DebugInfo().GetUnitAtIndex(0);
+  ASSERT_TRUE(unit);
+
+  auto make_namespace = [](llvm::StringRef name) {
+    return CompilerContext(CompilerContextKind::Namespace, ConstString(name));
+  };
+  auto make_struct = [](llvm::StringRef name) {
+    return CompilerContext(CompilerContextKind::Struct, ConstString(name));
+  };
+  DWARFDIE struct_die = unit->DIE().GetFirstChild().GetFirstChild();
+  ASSERT_TRUE(struct_die);
+  EXPECT_THAT(
+      struct_die.GetDeclContext(),
+      testing::ElementsAre(make_namespace("NAMESPACE"), make_struct("STRUCT")));
+  EXPECT_THAT(
+      struct_die.GetTypeLookupContext(),
+      testing::ElementsAre(make_namespace("NAMESPACE"), make_struct("STRUCT")));
+}