Fix for DWARF parsing to better handle auto return type for member functions

[shafik]

Summary

Currently when we have a member function that has an auto return type and the definition is out of line we generate two DWARF DIE.
One for the declaration and a second one for the definition. We don't currently lookup the definition in order to replace the auto return type with a real one.

This modifies DWARFASTParserClang to detect we have a function with deduced return type and lookup the
definition to obtain the correct return type and adjust the FunctionDecl to reflect this.

[aprantl]

I think it would be best to split out the Clang change into a separately tested patch.

clang/lib/CodeGen/CGDebugInfo.cpp

1694 ↗

(On Diff #356843)

typo: definition (2x)

[aprantl]

I think it would be best to split out the Clang change into a separately tested patch.

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

2783

This block looks like it's more complicated than it needs to be. Could you just say

if (other_die != die)
      if (other_die.Tag()) != DW_TAG_subprogram)
       return false;

or am I missing something?

[aprantl]

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

2783

Definitely missed something :-)

if (other_die == die || (other_die.Tag()) != DW_TAG_subprogram))
    return false;

[aprantl]

Could LLDB find the linkage name on the declaration, look that name up in the symbol table, and find the DW_TAG_subprogram DIE for the symbol's start address?

[shafik]

Changing approach based on Adrian's comments.

[shafik]

@aprantl after your comments and discussion offline I changed my approach to do this lookup using the symbol table and it worked out.

The main issue with the first approach was that gcc would also have to be updated in order for them to change their approach to generating debug info as well and that felt a lot harder to justify.

This is also a simpler approach, it requires fewer changes.

[probinson]

Currently when we have a member function that has an auto return type and the definition is out of line we generate two DWARF DIE.
One for the declaration and a second one for the definition, the definition holds the deduced type but does not contain a DW_AT_name nor
a DW_AT_linkage_name so there was not way to look up the definition DIE.

Regarding the DWARF, the definition DIE should have a DW_AT_specification that points back to the declaration; is that missing here?
I'm not familiar with LLDB so it's likely I'm misunderstanding the problem.

[shafik]

In D105564#2867717, @probinson wrote:

Currently when we have a member function that has an auto return type and the definition is out of line we generate two DWARF DIE.
One for the declaration and a second one for the definition, the definition holds the deduced type but does not contain a DW_AT_name nor
a DW_AT_linkage_name so there was not way to look up the definition DIE.

Regarding the DWARF, the definition DIE should have a DW_AT_specification that points back to the declaration; is that missing here?
I'm not familiar with LLDB so it's likely I'm misunderstanding the problem.

Apologies, I should have updated the description as well, portions of that description are out of date with the new approach I just updated to.

[teemperor]

I think this looks good, thanks for fixing this! I believe there should be a few more tests for all the corner cases we can run into here (those tests can all be just Python API tests, no need for having them all in assembly format). Also I think lambdas where triggering the original issue, so that would also be nice to have in a test.

I started writing some example tests but this is crashing for me with:

Unexpected undeduced type!
UNREACHABLE executed at /home/teemperor/work/ci/llvm-project/clang/lib/CodeGen/CodeGenTypes.cpp:624!
PLEASE submit a bug report to https://bugs.llvm.org/ and include the crash backtrace.
Stack dump:
0.	Program arguments: ./bin/lldb ././lldb-test-build.noindex/lang/cpp/auto_return/TestCppAutoReturn.test_dwarf/a.out
 #0 0x000055f540b5e611 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (./bin/lldb+0x34611)
 #1 0x000055f540b5c6b0 llvm::sys::RunSignalHandlers() (./bin/lldb+0x326b0)
 #2 0x000055f540b5efb6 SignalHandler(int) (./bin/lldb+0x34fb6)
 #3 0x00007fe3c3484870 __restore_rt (/usr/lib/libpthread.so.0+0x13870)
 #4 0x00007fe3bd2e3d22 raise (/usr/lib/libc.so.6+0x3cd22)
 #5 0x00007fe3bd2cd862 abort (/usr/lib/libc.so.6+0x26862)
 #6 0x00007fe3becf0df1 (/home/teemperor/work/ci/build/bin/../lib/liblldb.so.13git+0x146adf1)
 #7 0x00007fe3bf7cbdda clang::CodeGen::CodeGenTypes::ConvertType(clang::QualType) (/home/teemperor/work/ci/build/bin/../lib/liblldb.so.13git+0x1f45dda)
 #8 0x00007fe3bf7caf7e clang::CodeGen::CodeGenTypes::ConvertTypeForMem(clang::QualType, bool) (/home/teemperor/work/ci/build/bin/../lib/liblldb.so.13git+0x1f44f7e)
 #9 0x00007fe3bf951dd8 clang::CodeGen::CodeGenModule::getOrCreateStaticVarDecl(clang::VarDecl const&, llvm::GlobalValue::LinkageTypes) (/home/teemperor/work/ci/build/bin/../lib/liblldb.so.13git+0x20cbdd8)
#10 0x00007fe3bf950b10 clang::CodeGen::CodeGenFunction::EmitStaticVarDecl(clang::VarDecl const&, llvm::GlobalValue::LinkageTypes) (/home/teemperor/work/ci/build/bin/../lib/liblldb.so.13git+0x20cab10)
#11 0x00007fe3bf9508f3 clang::CodeGen::CodeGenFunction::EmitVarDecl(clang::VarDecl const&) (/home/teemperor/work/ci/build/bin/../lib/liblldb.so.13git+0x20ca8f3)
#12 0x00007fe3bf950458 clang::CodeGen::CodeGenFunction::EmitDecl(clang::Decl const&) (/home/teemperor/work/ci/build/bin/../lib/liblldb.so.13git+0x20ca458)
#13 0x00007fe3bf6f887c clang::CodeGen::CodeGenFunction::EmitDeclStmt(clang::DeclStmt const&) (/home/teemperor/work/ci/build/bin/../lib/liblldb.so.13git+0x1e7287c)
#14 0x00007fe3bf6ee2d8 clang::CodeGen::CodeGenFunction::EmitSimpleStmt(clang::Stmt const*, llvm::ArrayRef<clang::Attr const*>) (/home/teemperor/work/ci/build/bin/../lib/liblldb.so.13git+0x1e682d8)
#15 0x00007fe3bf6eda89 clang::CodeGen::CodeGenFunction::EmitStmt(clang::Stmt const*, llvm::ArrayRef<clang::Attr const*>) (/home/teemperor/work/ci/build/bin/../lib/liblldb.so.13git+0x1e67a89)
#16 0x00007fe3bf6f96b0 clang::CodeGen::CodeGenFunction::EmitCompoundStmtWithoutScope(clang::CompoundStmt const&, bool, clang::CodeGen::AggValueSlot) (/home/teemperor/work/ci/build/bin/../lib/liblldb.so.13git+0x1e736b0)
#17 0x00007fe3bf7585b4 clang::CodeGen::CodeGenFunction::EmitFunctionBody(clang::Stmt const*) (/home/teemperor/work/ci/build/bin/../lib/liblldb.so.13git+0x1ed25b4)
#18 0x00007fe3bf7591de clang::CodeGen::CodeGenFunction::GenerateCode(clang::GlobalDecl, llvm::Function*, clang::CodeGen::CGFunctionInfo const&) (/home/teemperor/work/ci/build/bin/../lib/liblldb.so.13git+0x1ed31de)
#19 0x00007fe3bf77a51f clang::CodeGen::CodeGenModule::EmitGlobalFunctionDefinition(clang::GlobalDecl, llvm::GlobalValue*) (/home/teemperor/work/ci/build/bin/../lib/liblldb.so.13git+0x1ef451f)
#20 0x00007fe3bf77222d clang::CodeGen::CodeGenModule::EmitGlobalDefinition(clang::GlobalDecl, llvm::GlobalValue*) (/home/teemperor/work/ci/build/bin/../lib/liblldb.so.13git+0x1eec22d)
#21 0x00007fe3bf7773bb clang::CodeGen::CodeGenModule::EmitGlobal(clang::GlobalDecl) (/home/teemperor/work/ci/build/bin/../lib/liblldb.so.13git+0x1ef13bb)
#22 0x00007fe3bf77e039 clang::CodeGen::CodeGenModule::EmitTopLevelDecl(clang::Decl*) (/home/teemperor/work/ci/build/bin/../lib/liblldb.so.13git+0x1ef8039)
#23 0x00007fe3bf6ab280 (anonymous namespace)::CodeGeneratorImpl::HandleTopLevelDecl(clang::DeclGroupRef) (/home/teemperor/work/ci/build/bin/../lib/liblldb.so.13git+0x1e25280)
#24 0x00007fe3bf549632 lldb_private::ASTResultSynthesizer::HandleTopLevelDecl(clang::DeclGroupRef) (/home/teemperor/work/ci/build/bin/../lib/liblldb.so.13git+0x1cc3632)
#25 0x00007fe3c018a558 clang::ParseAST(clang::Sema&, bool, bool) (/home/teemperor/work/ci/build/bin/../lib/liblldb.so.13git+0x2904558)
#26 0x00007fe3bf55d493 lldb_private::ClangExpressionParser::ParseInternal(lldb_private::DiagnosticManager&, clang::CodeCompleteConsumer*, unsigned int, unsigned int) (/home/teemperor/work/ci/build/bin/../lib/liblldb.so.13git+0x1cd7493)
#27 0x00007fe3bf540c11 lldb_private::ClangUserExpression::TryParse(lldb_private::DiagnosticManager&, lldb_private::ExecutionContextScope*, lldb_private::ExecutionContext&, lldb_private::ExecutionPolicy, bool, bool) (/home/teemperor/work/ci/build/bin/../lib/liblldb.so.13git+0x1cbac11)
#28 0x00007fe3bf541346 lldb_private::ClangUserExpression::Parse(lldb_private::DiagnosticManager&, lldb_private::ExecutionContext&, lldb_private::ExecutionPolicy, bool, bool) (/home/teemperor/work/ci/build/bin/../lib/liblldb.so.13git+0x1cbb346)
#29 0x00007fe3be8013d6 lldb_private::UserExpression::Evaluate(lldb_private::ExecutionContext&, lldb_private::EvaluateExpressionOptions const&, llvm::StringRef, llvm::StringRef, std::shared_ptr<lldb_private::ValueObject>&, lldb_private::Status&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >*, lldb_private::ValueObject*) (/home/teemperor/work/ci/build/bin/../lib/liblldb.so.13git+0xf7b3d6)
#30 0x00007fe3be927184 lldb_private::Target::EvaluateExpression(llvm::StringRef, lldb_private::ExecutionContextScope*, std::shared_ptr<lldb_private::ValueObject>&, lldb_private::EvaluateExpressionOptions const&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >*, lldb_private::ValueObject*) (/home/teemperor/work/ci/build/bin/../lib/liblldb.so.13git+0x10a1184)
#31 0x00007fe3bf473723 lldb_private::CommandObjectExpression::EvaluateExpression(llvm::StringRef, lldb_private::Stream&, lldb_private::Stream&, lldb_private::CommandReturnObject&) (/home/teemperor/work/ci/build/bin/../lib/liblldb.so.13git+0x1bed723)
#32 0x00007fe3bf4746ae lldb_private::CommandObjectExpression::DoExecute(llvm::StringRef, lldb_private::CommandReturnObject&) (/home/teemperor/work/ci/build/bin/../lib/liblldb.so.13git+0x1bee6ae)
#33 0x00007fe3be848635 lldb_private::CommandObjectRaw::Execute(char const*, lldb_private::CommandReturnObject&) (/home/teemperor/work/ci/build/bin/../lib/liblldb.so.13git+0xfc2635)
#34 0x00007fe3be83d0a8 lldb_private::CommandInterpreter::HandleCommand(char const*, lldb_private::LazyBool, lldb_private::CommandReturnObject&) (/home/teemperor/work/ci/build/bin/../lib/liblldb.so.13git+0xfb70a8)
#35 0x00007fe3be840f58 lldb_private::CommandInterpreter::IOHandlerInputComplete(lldb_private::IOHandler&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >&) (/home/teemperor/work/ci/build/bin/../lib/liblldb.so.13git+0xfbaf58)
#36 0x00007fe3be781f18 lldb_private::IOHandlerEditline::Run() (/home/teemperor/work/ci/build/bin/../lib/liblldb.so.13git+0xefbf18)
#37 0x00007fe3be762cc4 lldb_private::Debugger::RunIOHandlers() (/home/teemperor/work/ci/build/bin/../lib/liblldb.so.13git+0xedccc4)
#38 0x00007fe3be842c19 lldb_private::CommandInterpreter::RunCommandInterpreter(lldb_private::CommandInterpreterRunOptions&) (/home/teemperor/work/ci/build/bin/../lib/liblldb.so.13git+0xfbcc19)
#39 0x00007fe3be2a16bd lldb::SBDebugger::RunCommandInterpreter(bool, bool) (/home/teemperor/work/ci/build/bin/../lib/liblldb.so.13git+0xa1b6bd)
#40 0x000055f540b39d0c Driver::MainLoop() (./bin/lldb+0xfd0c)

This is the diff for the test:

diff --git a/lldb/test/API/lang/cpp/auto_return/Makefile b/lldb/test/API/lang/cpp/auto_return/Makefile
new file mode 100644
index 000000000000..a43ca68df298
--- /dev/null
+++ b/lldb/test/API/lang/cpp/auto_return/Makefile
@@ -0,0 +1,4 @@
+CXX_SOURCES := main.cpp other.cpp
+CXXFLAGS_EXTRAS := -std=c++17
+
+include Makefile.rules
diff --git a/lldb/test/API/lang/cpp/auto_return/TestCppAutoReturn.py b/lldb/test/API/lang/cpp/auto_return/TestCppAutoReturn.py
new file mode 100644
index 000000000000..49ff5a9460dd
--- /dev/null
+++ b/lldb/test/API/lang/cpp/auto_return/TestCppAutoReturn.py
@@ -0,0 +1,18 @@
+import lldb
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+
+class TestCase(TestBase):
+
+    mydir = TestBase.compute_mydir(__file__)
+
+    def test(self):
+        self.build()
+        lldbutil.run_to_source_breakpoint(self, "// break here", lldb.SBFileSpec("main.cpp"))
+
+        # Member access
+        self.expect_expr("C.ret()", result_type="int", result_value="1")
+
+        lldbutil.run_to_source_breakpoint(self, "// break also here", lldb.SBFileSpec("other.cpp"))
+        self.expect_expr("b.ret()", result_type="int", result_value="1")
diff --git a/lldb/test/API/lang/cpp/auto_return/main.cpp b/lldb/test/API/lang/cpp/auto_return/main.cpp
new file mode 100644
index 000000000000..3629c7b0c8f4
--- /dev/null
+++ b/lldb/test/API/lang/cpp/auto_return/main.cpp
@@ -0,0 +1,18 @@
+void other();
+
+namespace {
+struct Bla {
+  auto ret();
+};
+
+auto Bla::ret() {
+  auto x = [](int bla){ return bla; };
+  return x(1);
+}
+}
+
+int main() {
+  Bla C;
+  other();
+  return C.ret(); // break here
+}
diff --git a/lldb/test/API/lang/cpp/auto_return/other.cpp b/lldb/test/API/lang/cpp/auto_return/other.cpp
new file mode 100644
index 000000000000..315049e16ff0
--- /dev/null
+++ b/lldb/test/API/lang/cpp/auto_return/other.cpp
@@ -0,0 +1,15 @@
+namespace {
+struct Bla {
+  auto ret();
+};
+
+auto Bla::ret() {
+  auto x = [](int bla){ return bla; };
+  return x(2);
+}
+}
+
+void other() {
+  Bla b;
+  b.ret(); // // break also here
+}

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

435

If this is virtual then I guess SymbolFileDWARFDwo should overload it?

[clayborg]

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

1359

s/defintion/definition/

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

2767

type

2779

check dcu to ensure it isn't NULL

[shafik]

• Modified FindTypeForAutoReturnForDIE to take into account if we have multiple symbols with the same name.
• Modified ParseSubroutine to take into account that case we get the definition first, this can happen when we set a breakpoint inside the definition.
• Added new tests suggested by Raphael.

[shafik]

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

435

I am actually not sure if this has to be virtual or not, let me dig into this and see if there would be any difference for SymbolFileDWARFDwo or not.

[teemperor]

I guess Phabricator just sent this back to review automatically when you updated the diff? Just mark this as 'needs review' again when this is ready for review. I'll send this back in the meantime to clear my review queue.

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

897

unused variable

946

unrelated change?

[JDevlieghere]

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

403–405

What's the purpose of this? Do we expect to see the type attribute more than once?

898–899

You're doing dyn_cast_or_null but then below you're dereferencing ts unconditionally?

1363–1365

LLVM likes to put these variables in the if-clause, which I personally really like because it conveys the scope without hurting readability.

1367–1370

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

2762–2765

I know this pattern is common in LLDB, but I really dislike it because you have to backtrack all the way to the beginning of the function to know if type_sp has been modified in any way. When I write code like, this I tend to use return {}; to make it clear I'm returning a default constructed instance of the return type. That also makes it clear where we're actually returning a non-default instance by just looking at the returns.

2808

[shafik]

• Removed virtual from FindTypeForAutoReturnForDIE
• Added missing nullptr checks
• Modernized the code

[shafik]

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

403–405

Good question, the first iteration was done by @teemperor and then I modified it heavily but I did not dig into this change to deeply but I was pretty sure when we first talked about there was a good reason for it.

1363–1365

Good catch, I was changing this code around a lot and forgot to go back and clean this up.

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

2762–2765

Good catch, I originally based this on FindCompleteObjCDefinitionTypeForDIE and stuck with the idiom w/o thinking about it.

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

435

Since this is based on the same approach in GetObjCClassSymbol and that is not virtual I am going to drop it.

[teemperor]

This comment was removed by teemperor.

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

403–405

ParsedDWARFTypeAttributes iterates not just over the attributes in the current DIE, but also follows DW_AT_specification and then iterates the attributes there. But the DW_AT_specification of the definition points to the declaration with the auto type, so without this change we would first assign type to the real type from the definition and then when we iterate over the attributes of the declaration we would overwrite the real type with the auto type.

In short: without this change ParsedDWARFTypeAttributes(definition_die).type would be auto instead of the real type.

[aprantl]

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

2783

should there be an early exit if we found other_die?

[shafik]

• Expanded test
• applied clang-format

[aprantl]

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

403

Could you add a comment explaining why this is necessary? (see conversation below)

lldb/source/Plugins/ExpressionParser/Clang/ASTResultSynthesizer.cpp

if (is_lvalue) {
 
     QualType ptr_qual_type;
 
     if (expr_qual_type->getAs<ObjCObjectType>() != nullptr)
       ptr_qual_type = Ctx.getObjCObjectPointerType(expr_qual_type);
     else
       ptr_qual_type = Ctx.getPointerType(expr_qual_type);
 
-    result_decl =
-        VarDecl::Create(Ctx, DC, SourceLocation(), SourceLocation(),
-                        result_ptr_id, ptr_qual_type, nullptr, SC_Static);
+    TypeSourceInfo *tsi = Ctx.getTrivialTypeSourceInfo(
+        ptr_qual_type, last_expr->getSourceRange().getBegin());
+
+    result_decl = VarDecl::Create(Ctx, DC, SourceLocation(), SourceLocation(),
+                                  result_ptr_id, ptr_qual_type, tsi, SC_Static);
 
     if (!result_decl)
       return false;
 
     ExprResult address_of_expr =
         m_sema->CreateBuiltinUnaryOp(SourceLocation(), UO_AddrOf, last_expr);
     if (address_of_expr.get())
       m_sema->AddInitializerToDecl(result_decl, address_of_expr.get(), true);
     else
       return false;
   } else {
     IdentifierInfo &result_id = Ctx.Idents.get("$__lldb_expr_result");
 
-    result_decl =
-        VarDecl::Create(Ctx, DC, SourceLocation(), SourceLocation(), &result_id,
-                        expr_qual_type, nullptr, SC_Static);
+    TypeSourceInfo *tsi = Ctx.getTrivialTypeSourceInfo(
+        expr_qual_type, last_expr->getSourceRange().getBegin());
+    result_decl = VarDecl::Create(Ctx, DC, SourceLocation(), SourceLocation(),
+                                  &result_id, expr_qual_type, tsi, SC_Static);
 
     if (!result_decl)
       return false;
 
     m_sema->AddInitializerToDecl(result_decl, last_expr, true);
   }
 
   DC->addDecl(result_decl);

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

case DW_AT_signature:
       signature = form_value;
       break;
 
     case DW_AT_specification:
       specification = form_value;
       break;
 
     case DW_AT_type:
+      if (!type.IsValid())
         type = form_value;
       break;
 
     case DW_AT_virtuality:
       is_virtual = form_value.Boolean();
       break;
 
     case DW_AT_APPLE_objc_complete_type:
       is_complete_objc_class = form_value.Signed();
       break;
default:
     break;
 
   case DW_TAG_unspecified_type:
     if (attrs.name == "nullptr_t" || attrs.name == "decltype(nullptr)") {
       resolve_state = Type::ResolveState::Full;
       clang_type = m_ast.GetBasicType(eBasicTypeNullPtr);
       break;
     }
+    if (attrs.name == "auto") {
+      resolve_state = Type::ResolveState::Full;
+      clang::QualType t = m_ast.getASTContext().getAutoDeductType();
+      clang_type = m_ast.GetType(t);
+      break;
+    }
     // Fall through to base type below in case we can handle the type
     // there...
     LLVM_FALLTHROUGH;
 
   case DW_TAG_base_type:
     resolve_state = Type::ResolveState::Full;
     clang_type = m_ast.GetBuiltinTypeForDWARFEncodingAndBitSize(
         attrs.name.GetStringRef(), attrs.encoding,
case llvm::dwarf::DW_CC_normal:
     return clang::CC_C;
   case llvm::dwarf::DW_CC_BORLAND_stdcall:
     return clang::CC_X86StdCall;
   case llvm::dwarf::DW_CC_BORLAND_msfastcall:
     return clang::CC_X86FastCall;
   case llvm::dwarf::DW_CC_LLVM_vectorcall:
     return clang::CC_X86VectorCall;
   case llvm::dwarf::DW_CC_BORLAND_pascal:
     return clang::CC_X86Pascal;
   case llvm::dwarf::DW_CC_LLVM_Win64:
     return clang::CC_Win64;
   case llvm::dwarf::DW_CC_LLVM_X86_64SysV:
     return clang::CC_X86_64SysV;
   case llvm::dwarf::DW_CC_LLVM_X86RegCall:
     return clang::CC_X86RegCall;
   default:
     break;
   }
 
   Log *log = GetLog(DWARFLog::TypeCompletion | DWARFLog::Lookups);
   LLDB_LOG(log, "Unsupported DW_AT_calling_convention value: {0}",
            attrs.calling_convention);
   // Use the default calling convention as a fallback.
   return clang::CC_C;
 }
 
+static void maybePropagateDeducedReturnType(clang::DeclContext *decl_ctx,
+                                            clang::ASTContext &ast,
+                                            CompilerType function_type) {
+  auto *function_decl = llvm::dyn_cast_or_null<clang::FunctionDecl>(decl_ctx);
+
+  if (!function_decl)
+    return;
+
+  if (!function_decl->getReturnType()->isUndeducedAutoType())
+    return;
+
+  if (TypeSystemClang *ts = llvm::dyn_cast_or_null<TypeSystemClang>(
+          function_type.GetTypeSystem()))
+    ast.adjustDeducedFunctionResultType(
+        function_decl, ClangUtil::GetQualType(ts->GetFunctionReturnType(
+                           function_type.GetOpaqueQualType())));
+}
+
 TypeSP DWARFASTParserClang::ParseSubroutine(const DWARFDIE &die,
                            ParsedDWARFTypeAttributes &attrs) {
   Log *log = GetLog(DWARFLog::TypeCompletion | DWARFLog::Lookups);
 
   SymbolFileDWARF *dwarf = die.GetDWARF();
   const dw_tag_t tag = die.Tag();
 
   bool is_variadic = false;
if (func_type)
     return_clang_type = func_type->GetForwardCompilerType();
   else
     return_clang_type = m_ast.GetBasicType(eBasicTypeVoid);
 
   std::vector<CompilerType> function_param_types;
   std::vector<clang::ParmVarDecl *> function_param_decls;
 
   // Parse the function children for the parameters
 
   DWARFDIE decl_ctx_die;
   clang::DeclContext *containing_decl_ctx =
       GetClangDeclContextContainingDIE(die, &decl_ctx_die);
   const clang::Decl::Kind containing_decl_kind =
       containing_decl_ctx->getDeclKind();
 
   bool is_cxx_method = DeclKindIsCXXClass(containing_decl_kind);
   // Start off static. This will be set to false in
clang::CallingConv calling_convention =
       ConvertDWARFCallingConventionToClang(attrs);
 
   // clang_type will get the function prototype clang type after this
   // call
   CompilerType clang_type = m_ast.CreateFunctionType(
       return_clang_type, function_param_types.data(),
       function_param_types.size(), is_variadic, type_quals, calling_convention);
 
+  if (attrs.specification.IsValid()) {
+    DWARFDIE abs_die = attrs.specification.Reference();
+    if (dwarf->ResolveType(abs_die)) {
+      maybePropagateDeducedReturnType(GetCachedClangDeclContextForDIE(abs_die),
+                                      m_ast.getASTContext(), clang_type);
+    }
+  }
+
   if (attrs.name) {
     bool type_handled = false;
     if (tag == DW_TAG_subprogram || tag == DW_TAG_inlined_subroutine) {
       ObjCLanguage::MethodName objc_method(attrs.name.GetStringRef(), true);
       if (objc_method.IsValid(true)) {
         CompilerType class_opaque_type;
         ConstString class_name(objc_method.GetClassName());
         if (class_name) {
if (!type_handled) {
                       object_pointer_name.c_str(),
                       static_cast<void *>(function_decl));
           }
           m_ast.SetMetadata(function_decl, metadata);
         }
       }
     }
   }
+
+  // If a function has an auto return type we need to find the definition since
+  // that will have the deduced return type and adjust the FunctionDecl to
+  // reflect this.
+  if (func_type && func_type->GetName() == "auto") {
+    if (TypeSP ret_type = dwarf->FindTypeForAutoReturnForDIE(
+            die, ConstString(attrs.mangled_name))) {
+      return_clang_type = ret_type->GetForwardCompilerType();
+      if (auto *function_decl = llvm::dyn_cast_or_null<clang::FunctionDecl>(
+              GetCachedClangDeclContextForDIE(die)))
+        m_ast.getASTContext().adjustDeducedFunctionResultType(
+            function_decl, ClangUtil::GetQualType(return_clang_type));
+    }
+  }
+
   return std::make_shared<Type>(
       die.GetID(), dwarf, attrs.name, llvm::None, nullptr, LLDB_INVALID_UID,
       Type::eEncodingIsUID, &attrs.decl, clang_type, Type::ResolveState::Full);
 }
 
 TypeSP DWARFASTParserClang::ParseArrayType(const DWARFDIE &die,
                                            ParsedDWARFTypeAttributes &attrs) {
   SymbolFileDWARF *dwarf = die.GetDWARF();

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

protected:
   virtual lldb::TypeSP
   FindDefinitionTypeForDWARFDeclContext(const DWARFDeclContext &die_decl_ctx);
 
   virtual lldb::TypeSP
   FindCompleteObjCDefinitionTypeForDIE(const DWARFDIE &die,
                                        lldb_private::ConstString type_name,
                                        bool must_be_implementation);
 
+  lldb::TypeSP FindTypeForAutoReturnForDIE(const DWARFDIE &die,
+                                           lldb_private::ConstString name);
+
   lldb_private::Symbol *
   GetObjCClassSymbol(lldb_private::ConstString objc_class_name);
 
   lldb::TypeSP GetTypeForDIE(const DWARFDIE &die,
                              bool resolve_function_context = false);
 
   void SetDebugMapModule(const lldb::ModuleSP &module_sp) {
     m_debug_map_module_wp = module_sp;

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

m_index->GetCompleteObjCClass(
         if (die)
           GetDIEToType()[die.GetDIE()] = resolved_type;
         type_sp = resolved_type->shared_from_this();
         return false;
       });
   return type_sp;
 }
 
+lldb::TypeSP
+SymbolFileDWARF::FindTypeForAutoReturnForDIE(const DWARFDIE &die,
+                                             lldb_private::ConstString name) {
+  if (!name)
+    return {};
+
+  DWARFDIE other_die;
+  if (m_objfile_sp) {
+    Symtab *symtab = m_objfile_sp->GetSymtab();
+    if (symtab) {
+      std::vector<uint32_t> symbol_indexes;
+      symtab->FindAllSymbolsWithNameAndType(
+          name, eSymbolTypeAny, Symtab::eDebugAny, Symtab::eVisibilityAny,
+          symbol_indexes);
+
+      DWARFUnit *unit = die.GetCU();
+      DWARFCompileUnit *dcu = llvm::cast_or_null<DWARFCompileUnit>(unit);
+
+      if (!dcu)
+        return {};
+
+      for (size_t index = 0; index < symbol_indexes.size() && !other_die;
+           ++index) {
+        other_die = dcu->LookupAddress(
+            symtab->SymbolAtIndex(symbol_indexes[index])->GetFileAddress());
+      }
+    }
+  }
+
+  if (!other_die)
+    return {};
+
+  Type *resolved_type = ResolveType(other_die, false, true);
+
+  if (!resolved_type || resolved_type == DIE_IS_BEING_PARSED)
+    return {};
+
+  ParsedDWARFTypeAttributes attrs(other_die);
+  Type *func_type = nullptr;
+
+  if (attrs.specification.IsValid())
+    if (attrs.type.IsValid()) {
+      func_type = ResolveTypeUID(attrs.type.Reference(), true);
+
+      if (!func_type || func_type == DIE_IS_BEING_PARSED)
+        return {};
+
+      return func_type->shared_from_this();
+    }
+
+  return {};
+}
+
 // This function helps to ensure that the declaration contexts match for two
 // different DIEs. Often times debug information will refer to a forward
 // declaration of a type (the equivalent of "struct my_struct;". There will
 // often be a declaration of that type elsewhere that has the full definition.
 // When we go looking for the full type "my_struct", we will find one or more
 // matches in the accelerator tables and we will then need to make sure the
 // type was in the same declaration context as the original DIE. This function
 // can efficiently compare two DIEs and will return true when the declaration

lldb/test/API/lang/cpp/auto_return/Makefile

+CXX_SOURCES := main.cpp other.cpp
+CXXFLAGS_EXTRAS := -std=c++17
+
+include Makefile.rules

lldb/test/API/lang/cpp/auto_return/TestCppAutoReturn.py

+import lldb
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+
+class TestCppAutoReturn(TestBase):
+
+    mydir = TestBase.compute_mydir(__file__)
+
+    def test(self):
+        self.build()
+        lldbutil.run_to_source_breakpoint(self, "// break here", lldb.SBFileSpec("main.cpp"))
+
+        self.expect_expr("globalAutoRetFun()", result_type="int", result_value="10")
+        self.expect_expr("globalAutoRetFunFwdDecl()", result_type="int", result_value="11")
+
+        self.expect_expr("swumfGlobal.f1()", result_type="float", result_value="1")
+        self.expect_expr("swumfGlobal.f2()", result_type="int", result_value="1212")
+
+        self.expect_expr("swumfLocal.f1()", result_type="float", result_value="1")
+        self.expect_expr("swumfLocal.f2()", result_type="int", result_value="1212")
+
+        self.expect_expr("globalLambda()", result_type="Dummy", result_children=[ValueCheck(type="int", name="x", value="8")])
+
+        self.expect_expr("NS::namespaceFunc()", result_type="unsigned int", result_value="1")
+        self.expect_expr("NS::namespaceLambda()", result_type="unsigned int", result_value="2")
+        self.expect_expr("NS::StructInNamespace{}.f()", result_type="unsigned int", result_value="3")
+
+        self.expect_expr("tsful.f()", result_type="unsigned long", result_value="4")
+
+        self.expect_expr("w.f()", result_type="int", result_value="1")
+
+        lldbutil.run_to_source_breakpoint(self, "// break also here", lldb.SBFileSpec("other.cpp"))
+        self.expect_expr("w.f()", result_type="int", result_value="1")
+
+
+    @skipIf
+    def FailingTest(self):
+      self.build()
+      lldbutil.run_to_source_breakpoint(self, "// break here", lldb.SBFileSpec("main.cpp"))
+
+      ## rdar://92676775
+      self.expect_expr("localLambda()", result_type="int", result_value="100")

lldb/test/API/lang/cpp/auto_return/main.cpp

+auto globalAutoRetFun() { return 10; }
+
+auto globalAutoRetFunFwdDecl();
+auto globalAutoRetFunFwdDecl() { return 11; }
+
+struct StructWithAutoMemFuns {
+  auto f1();                 // Return type deduced out of line
+  auto f2() { return 1212; } // Return deduced inline
+};
+
+StructWithAutoMemFuns swumfGlobal;
+
+auto StructWithAutoMemFuns::f1() { return 1.f; }
+
+struct Dummy {
+  int x = 8;
+};
+
+auto globalLambda = []() { return Dummy{}; };
+
+namespace NS {
+auto namespaceFunc() { return 1u; }
+
+auto namespaceLambda = []() { return 2u; };
+
+struct StructInNamespace {
+  auto f() { return 3u; }
+};
+} // namespace NS
+
+template <typename T> struct TempStruct {
+  auto f() { return static_cast<T>(4); }
+};
+
+template <typename T> using TSF = TempStruct<T>;
+
+using TSFUL = TSF<unsigned long>;
+
+void other();
+
+namespace {
+struct Wrapper {
+  auto f();
+};
+
+auto Wrapper::f() {
+  auto x = [](int y) { return y; };
+  return x(1);
+}
+} // namespace
+
+int main() {
+  StructWithAutoMemFuns swumfLocal;
+  TSFUL tsful;
+
+  auto localLambda = []() { return 100; };
+
+  Wrapper w;
+  other();
+  return globalLambda().x + globalAutoRetFun() + globalAutoRetFunFwdDecl() +
+         w.f() + swumfGlobal.f1() + swumfLocal.f2() + NS::namespaceFunc() +
+         NS::namespaceLambda() + NS::StructInNamespace{}.f() + tsful.f() +
+         localLambda(); // break here
+}

lldb/test/API/lang/cpp/auto_return/other.cpp

+namespace {
+struct Wrapper {
+  auto f();
+};
+
+auto Wrapper::f() {
+  auto x = [](int y) { return y; };
+  return x(2);
+}
+} // namespace
+
+void other() {
+  Wrapper w;
+  w.f(); // // break also here
+}

lldb/test/Shell/SymbolFile/DWARF/x86/auto_return_symtab.s

+# This tests that lldb when using symbol table we are able to find the definition
+# for an auto return function.
+
+# RUN: llvm-mc -triple x86_64-apple-macosx10.15.0 %s -filetype=obj > %t.o
+# RUN: lldb-test symbols --dump-clang-ast %t.o | FileCheck %s
+
+# CHECK: CXXMethodDecl {{.*}} <<invalid sloc>> <invalid sloc> f 'int ()'
+
+# This was compiled from the following code:
+#
+# struct A {
+#     auto f();
+# };
+#
+# auto A::f() {
+#     return 0;
+# }
+#
+# Compiled using:
+#
+#  -target x86_64-apple-macosx10.15.0
+#
+# and edited to remove some uneeded sections.
+
+  .section  __TEXT,__text,regular,pure_instructions
+  .globl  __ZN1A1fEv                      ## -- Begin function _ZN1A1fEv
+  .p2align  4, 0x90
+__ZN1A1fEv:                             ## @_ZN1A1fEv
+Lfunc_begin0:
+  .cfi_startproc
+## %bb.0:                               ## %entry
+  pushq %rbp
+  .cfi_def_cfa_offset 16
+  .cfi_offset %rbp, -16
+  movq  %rsp, %rbp
+  .cfi_def_cfa_register %rbp
+  movq  %rdi, -8(%rbp)
+Ltmp0:
+  xorl  %eax, %eax
+  popq  %rbp
+  retq
+Ltmp1:
+Lfunc_end0:
+  .cfi_endproc
+                                        ## -- End function
+  .section  __DWARF,__debug_abbrev,regular,debug
+Lsection_abbrev:
+  .byte 1                               ## Abbreviation Code
+  .byte 17                              ## DW_TAG_compile_unit
+  .byte 1                               ## DW_CHILDREN_yes
+  .byte 37                              ## DW_AT_producer
+  .byte 14                              ## DW_FORM_strp
+  .byte 19                              ## DW_AT_language
+  .byte 5                               ## DW_FORM_data2
+  .byte 3                               ## DW_AT_name
+  .byte 14                              ## DW_FORM_strp
+  .ascii  "\202|"                         ## DW_AT_LLVM_sysroot
+  .byte 14                              ## DW_FORM_strp
+  .ascii  "\357\177"                      ## DW_AT_APPLE_sdk
+  .byte 14                              ## DW_FORM_strp
+  .byte 16                              ## DW_AT_stmt_list
+  .byte 23                              ## DW_FORM_sec_offset
+  .byte 27                              ## DW_AT_comp_dir
+  .byte 14                              ## DW_FORM_strp
+  .byte 17                              ## DW_AT_low_pc
+  .byte 1                               ## DW_FORM_addr
+  .byte 18                              ## DW_AT_high_pc
+  .byte 6                               ## DW_FORM_data4
+  .byte 0                               ## EOM(1)
+  .byte 0                               ## EOM(2)
+  .byte 2                               ## Abbreviation Code
+  .byte 19                              ## DW_TAG_structure_type
+  .byte 1                               ## DW_CHILDREN_yes
+  .byte 54                              ## DW_AT_calling_convention
+  .byte 11                              ## DW_FORM_data1
+  .byte 3                               ## DW_AT_name
+  .byte 14                              ## DW_FORM_strp
+  .byte 11                              ## DW_AT_byte_size
+  .byte 11                              ## DW_FORM_data1
+  .byte 58                              ## DW_AT_decl_file
+  .byte 11                              ## DW_FORM_data1
+  .byte 59                              ## DW_AT_decl_line
+  .byte 11                              ## DW_FORM_data1
+  .byte 0                               ## EOM(1)
+  .byte 0                               ## EOM(2)
+  .byte 3                               ## Abbreviation Code
+  .byte 46                              ## DW_TAG_subprogram
+  .byte 1                               ## DW_CHILDREN_yes
+  .byte 110                             ## DW_AT_linkage_name
+  .byte 14                              ## DW_FORM_strp
+  .byte 3                               ## DW_AT_name
+  .byte 14                              ## DW_FORM_strp
+  .byte 58                              ## DW_AT_decl_file
+  .byte 11                              ## DW_FORM_data1
+  .byte 59                              ## DW_AT_decl_line
+  .byte 11                              ## DW_FORM_data1
+  .byte 73                              ## DW_AT_type
+  .byte 19                              ## DW_FORM_ref4
+  .byte 60                              ## DW_AT_declaration
+  .byte 25                              ## DW_FORM_flag_present
+  .byte 63                              ## DW_AT_external
+  .byte 25                              ## DW_FORM_flag_present
+  .byte 0                               ## EOM(1)
+  .byte 0                               ## EOM(2)
+  .byte 4                               ## Abbreviation Code
+  .byte 5                               ## DW_TAG_formal_parameter
+  .byte 0                               ## DW_CHILDREN_no
+  .byte 73                              ## DW_AT_type
+  .byte 19                              ## DW_FORM_ref4
+  .byte 52                              ## DW_AT_artificial
+  .byte 25                              ## DW_FORM_flag_present
+  .byte 0                               ## EOM(1)
+  .byte 0                               ## EOM(2)
+  .byte 5                               ## Abbreviation Code
+  .byte 59                              ## DW_TAG_unspecified_type
+  .byte 0                               ## DW_CHILDREN_no
+  .byte 3                               ## DW_AT_name
+  .byte 14                              ## DW_FORM_strp
+  .byte 0                               ## EOM(1)
+  .byte 0                               ## EOM(2)
+  .byte 6                               ## Abbreviation Code
+  .byte 15                              ## DW_TAG_pointer_type
+  .byte 0                               ## DW_CHILDREN_no
+  .byte 73                              ## DW_AT_type
+  .byte 19                              ## DW_FORM_ref4
+  .byte 0                               ## EOM(1)
+  .byte 0                               ## EOM(2)
+  .byte 7                               ## Abbreviation Code
+  .byte 46                              ## DW_TAG_subprogram
+  .byte 1                               ## DW_CHILDREN_yes
+  .byte 17                              ## DW_AT_low_pc
+  .byte 1                               ## DW_FORM_addr
+  .byte 18                              ## DW_AT_high_pc
+  .byte 6                               ## DW_FORM_data4
+  .byte 64                              ## DW_AT_frame_base
+  .byte 24                              ## DW_FORM_exprloc
+  .byte 100                             ## DW_AT_object_pointer
+  .byte 19                              ## DW_FORM_ref4
+  .byte 73                              ## DW_AT_type
+  .byte 19                              ## DW_FORM_ref4
+  .byte 59                              ## DW_AT_decl_line
+  .byte 11                              ## DW_FORM_data1
+  .byte 71                              ## DW_AT_specification
+  .byte 19                              ## DW_FORM_ref4
+  .byte 0                               ## EOM(1)
+  .byte 0                               ## EOM(2)
+  .byte 8                               ## Abbreviation Code
+  .byte 5                               ## DW_TAG_formal_parameter
+  .byte 0                               ## DW_CHILDREN_no
+  .byte 2                               ## DW_AT_location
+  .byte 24                              ## DW_FORM_exprloc
+  .byte 3                               ## DW_AT_name
+  .byte 14                              ## DW_FORM_strp
+  .byte 73                              ## DW_AT_type
+  .byte 19                              ## DW_FORM_ref4
+  .byte 52                              ## DW_AT_artificial
+  .byte 25                              ## DW_FORM_flag_present
+  .byte 0                               ## EOM(1)
+  .byte 0                               ## EOM(2)
+  .byte 9                               ## Abbreviation Code
+  .byte 36                              ## DW_TAG_base_type
+  .byte 0                               ## DW_CHILDREN_no
+  .byte 3                               ## DW_AT_name
+  .byte 14                              ## DW_FORM_strp
+  .byte 62                              ## DW_AT_encoding
+  .byte 11                              ## DW_FORM_data1
+  .byte 11                              ## DW_AT_byte_size
+  .byte 11                              ## DW_FORM_data1
+  .byte 0                               ## EOM(1)
+  .byte 0                               ## EOM(2)
+  .byte 0                               ## EOM(3)
+  .section  __DWARF,__debug_info,regular,debug
+Lsection_info:
+Lcu_begin0:
+.set Lset0, Ldebug_info_end0-Ldebug_info_start0 ## Length of Unit
+  .long Lset0
+Ldebug_info_start0:
+  .short  4                               ## DWARF version number
+.set Lset1, Lsection_abbrev-Lsection_abbrev ## Offset Into Abbrev. Section
+  .long Lset1
+  .byte 8                               ## Address Size (in bytes)
+  .byte 1                               ## Abbrev [1] 0xb:0x86 DW_TAG_compile_unit
+  .long 0                               ## DW_AT_producer
+  .short  33                              ## DW_AT_language
+  .long 105                             ## DW_AT_name
+  .long 129                             ## DW_AT_LLVM_sysroot
+  .long 185                             ## DW_AT_APPLE_sdk
+.set Lset2, Lline_table_start0-Lsection_line ## DW_AT_stmt_list
+  .long Lset2
+  .long 200                             ## DW_AT_comp_dir
+  .quad Lfunc_begin0                    ## DW_AT_low_pc
+.set Lset3, Lfunc_end0-Lfunc_begin0     ## DW_AT_high_pc
+  .long Lset3
+  .byte 2                               ## Abbrev [2] 0x32:0x1f DW_TAG_structure_type
+  .byte 5                               ## DW_AT_calling_convention
+  .long 219                             ## DW_AT_name
+  .byte 1                               ## DW_AT_byte_size
+  .byte 1                               ## DW_AT_decl_file
+  .byte 1                               ## DW_AT_decl_line
+  .byte 3                               ## Abbrev [3] 0x3b:0x15 DW_TAG_subprogram
+  .long 221                             ## DW_AT_linkage_name
+  .long 231                             ## DW_AT_name
+  .byte 1                               ## DW_AT_decl_file
+  .byte 2                               ## DW_AT_decl_line
+  .long 81                              ## DW_AT_type
+                                        ## DW_AT_declaration
+                                        ## DW_AT_external
+  .byte 4                               ## Abbrev [4] 0x4a:0x5 DW_TAG_formal_parameter
+  .long 86                              ## DW_AT_type
+                                        ## DW_AT_artificial
+  .byte 0                               ## End Of Children Mark
+  .byte 0                               ## End Of Children Mark
+  .byte 5                               ## Abbrev [5] 0x51:0x5 DW_TAG_unspecified_type
+  .long 233                             ## DW_AT_name
+  .byte 6                               ## Abbrev [6] 0x56:0x5 DW_TAG_pointer_type
+  .long 50                              ## DW_AT_type
+  .byte 7                               ## Abbrev [7] 0x5b:0x29 DW_TAG_subprogram
+  .quad Lfunc_begin0                    ## DW_AT_low_pc
+.set Lset4, Lfunc_end0-Lfunc_begin0     ## DW_AT_high_pc
+  .long Lset4
+  .byte 1                               ## DW_AT_frame_base
+  .byte 86
+  .long 119                             ## DW_AT_object_pointer
+  .long 132                             ## DW_AT_type
+  .byte 5                               ## DW_AT_decl_line
+  .long 59                              ## DW_AT_specification
+  .byte 8                               ## Abbrev [8] 0x77:0xc DW_TAG_formal_parameter
+  .byte 2                               ## DW_AT_location
+  .byte 145
+  .byte 120
+  .long 242                             ## DW_AT_name
+  .long 139                             ## DW_AT_type
+                                        ## DW_AT_artificial
+  .byte 0                               ## End Of Children Mark
+  .byte 9                               ## Abbrev [9] 0x84:0x7 DW_TAG_base_type
+  .long 238                             ## DW_AT_name
+  .byte 5                               ## DW_AT_encoding
+  .byte 4                               ## DW_AT_byte_size
+  .byte 6                               ## Abbrev [6] 0x8b:0x5 DW_TAG_pointer_type
+  .long 50                              ## DW_AT_type
+  .byte 0                               ## End Of Children Mark
+Ldebug_info_end0:
+  .section  __DWARF,__debug_str,regular,debug
+Linfo_string:
+  .asciz  "clang version 13.0.0 (https://github.com/llvm/llvm-project.git 18c3c7784975700ae463bb461487d46e74324a66)" ## string offset=0
+  .asciz  "auto_return_minimum.cpp"       ## string offset=105
+  .asciz  "/Library/Developer/CommandLineTools/SDKs/MacOSX11.3.sdk" ## string offset=129
+  .asciz  "MacOSX11.3.sdk"                ## string offset=185
+  .asciz  "/Users/shafik/code"            ## string offset=200
+  .asciz  "A"                             ## string offset=219
+  .asciz  "_ZN1A1fEv"                     ## string offset=221
+  .asciz  "f"                             ## string offset=231
+  .asciz  "auto"                          ## string offset=233
+  .asciz  "int"                           ## string offset=238
+  .asciz  "this"                          ## string offset=242
+Lsection_line:
+Lline_table_start0: