Fully handle globals and functions in CGDebugInfo::getDeclarationOrDefinition()

[friss]

Summary

Currently this function would return nothing for functions or globals that
haven't seen a definition yet. Make it return a forward declaration that will
get RAUWed with the definition if one is seen at a later point. The strategy
used to implement this is similar to what's done for types: the forward
declarations are stored in a vector and post processed upon finilization to
perform the required RAUWs.

For now the only user of getDeclarationOrDefinition() is EmitUsingDecl(), thus
this patch allows to emit correct imported declarations even in the absence of
an actual definition of the imported entity.

(Another user will be the debug info generation for argument default values
that I need to resurect).

This clang patch actually requires another trivial patch to LLVM before it can
go in (to handle forward declared globals). However, the test I'd like to commit
for the LLVM part contains the IR generated by this patch, thus I would have
found it a bit strange to commit it before this one is approved.

[friss]

ping

[dblaikie]

Looks pretty reasonable. Some optional and/or follow-up patch comments.

Have you considered if/how some of this could be unified with the type decl-or-def handling?

lib/CodeGen/CGDebugInfo.cpp

2310 ↗

(On Diff #15933)

If you want to submit these refactorings separately, feel free (& do that sort of thing without precommit review - just pulling out a bit of functionality and giving it a name is usually goodness even before the second user exists (we tend to have long functions that are hard to read - pulling out parts of them and giving them names usually makes them a bit easier to follow) - and it makes the code reviews more palatable (I can easily glance at a single function refactor like this, and mostly just assume you did the obvious thing of copy/paste the code and give it a name))

2310 ↗

(On Diff #15933)

Though the name 'collect' might be different from the existing similar functions we have for subprograms - could you check if we can have a more consistent naming one way or the other? (I think I named the subprogram ones 'apply' rather than 'collect')

Oh... I was confused, thought this was an LLVM patch (since it was sent to llvm-commits) so I was talking about LLVM codegen/asmprinter stuff...

Nevermind.

2406 ↗

(On Diff #15933)

Might be worth splitting the body of the if into its own function (& for symmetry, though it's shorter, the body of the else separately as well) so this function just immediately defers to variable or function handlers.

lib/CodeGen/CGDebugInfo.h

418 ↗

(On Diff #15933)

Typo of 'Fucntion'

[friss]

In D6173#5, @dblaikie wrote:

Looks pretty reasonable. Some optional and/or follow-up patch comments.

I'll commit that with your feedback addressed.

Have you considered if/how some of this could be unified with the type decl-or-def handling?

I kinda did, but there were some unclear points that made me chose the separate handling approach. Maybe you can shed some light on those:

• The TypeCache is keyed on the TagType itself. Unifying the map would mean keying on the canonical decl. I /think/ this should be fine, but I couldn't convince myself that I'm not missing something.
• In the finalize phase, the type replacement logic asserts that there always is a replacement type registered in the TypeCache, while for decls there might not be one. I'm not actually sure where the guarantee comes from on the type side.

lib/CodeGen/CGDebugInfo.cpp

2310 ↗

(On Diff #15933)

C'mon I did this mailing list mistake again... Sorry for the confusion.

[dblaikie]

In D6173#8, @friss wrote:

In D6173#5, @dblaikie wrote:

Looks pretty reasonable. Some optional and/or follow-up patch comments.

I'll commit that with your feedback addressed.

Have you considered if/how some of this could be unified with the type decl-or-def handling?

I kinda did, but there were some unclear points that made me chose the separate handling approach. Maybe you can shed some light on those:

• The TypeCache is keyed on the TagType itself. Unifying the map would mean keying on the canonical decl. I /think/ this should be fine, but I couldn't convince myself that I'm not missing something.

I think that should be fine - I forget how it all works, but I believe it's possible to go back & forth between the type and its canonical declaration... (ASTContext probably provides the help there)

• In the finalize phase, the type replacement logic asserts that there always is a replacement type registered in the TypeCache, while for decls there might not be one. I'm not actually sure where the guarantee comes from on the type side.

Yeah, we'd have to understand where that guarantee comes from. I think it might be because we (might) be creating stub metadata nodes before we even create the declaration (because we might end up with a definition and circular references, etc) - so the thing we're replacing is actually a stub, not even a declaration. That's only my wildest stab in the dark.

lib/CodeGen/CGDebugInfo.cpp

2310 ↗

(On Diff #15933)

No worries, I'm sure I've done it once or twice.

[friss]

Closed by commit rL222220 (authored by @friss).

cfe/trunk/lib/CodeGen/CGDebugInfo.h

class CGDebugInfo {
 
   /// RetainedTypes - list of interfaces we want to keep even if orphaned.
   std::vector<void *> RetainedTypes;
 
   /// ReplaceMap - Cache of forward declared types to RAUW at the end of
   /// compilation.
   std::vector<std::pair<const TagType *, llvm::WeakVH>> ReplaceMap;
 
+  /// \brief Cache of replaceable forward declarartions (functions and
+  /// variables) to RAUW at the end of compilation.
+  std::vector<std::pair<const DeclaratorDecl *, llvm::WeakVH>> FwdDeclReplaceMap;
+
   // LexicalBlockStack - Keep track of our current nested lexical block.
   std::vector<llvm::TrackingVH<llvm::MDNode> > LexicalBlockStack;
   llvm::DenseMap<const Decl *, llvm::WeakVH> RegionMap;
   // FnBeginRegionCount - Keep track of LexicalBlockStack counter at the
   // beginning of a function. This is used to pop unbalanced regions at
   // the end of a function.
   std::vector<unsigned> FnBeginRegionCount;
 
private:
   /// declaration for the given method definition.
   llvm::DISubprogram getFunctionDeclaration(const Decl *D);
 
   /// Return debug info descriptor to describe in-class static data member
   /// declaration for the given out-of-class definition.
   llvm::DIDerivedType
   getOrCreateStaticDataMemberDeclarationOrNull(const VarDecl *D);
 
+  /// \brief Create a DISubprogram describing the forward
+  /// decalration represented in the given FunctionDecl.
+  llvm::DISubprogram getFunctionForwardDeclaration(const FunctionDecl *FD);
+
+  /// \brief Create a DIGlobalVariable describing the forward
+  /// decalration represented in the given VarDecl.
+  llvm::DIGlobalVariable getGlobalVariableForwardDeclaration(const VarDecl *VD);
+
   /// Return a global variable that represents one of the collection of
   /// global variables created for an anonmyous union.
   llvm::DIGlobalVariable
   CollectAnonRecordDecls(const RecordDecl *RD, llvm::DIFile Unit, unsigned LineNo,
                          StringRef LinkageName, llvm::GlobalVariable *Var,
                          llvm::DIDescriptor DContext);
 
   /// getFunctionName - Get function name for the given FunctionDecl. If the

cfe/trunk/lib/CodeGen/CGDebugInfo.cpp

void CGDebugInfo::collectVarDeclProps(const VarDecl *VD, llvm::DIFile &Unit,
   // FIXME: Generalize this for even non-member global variables where the
   // declaration and definition may have different lexical decl contexts, once
   // we have support for emitting declarations of (non-member) global variables.
   VDContext = getContextDescriptor(
       dyn_cast<Decl>(VD->isStaticDataMember() ? VD->getLexicalDeclContext()
                                               : VD->getDeclContext()));
 }
 
+llvm::DISubprogram
+CGDebugInfo::getFunctionForwardDeclaration(const FunctionDecl *FD) {
+  llvm::DIArray TParamsArray;
+  StringRef Name, LinkageName;
+  unsigned Flags = 0;
+  SourceLocation Loc = FD->getLocation();
+  llvm::DIFile Unit = getOrCreateFile(Loc);
+  llvm::DIDescriptor DContext(Unit);
+  unsigned Line = getLineNumber(Loc);
+
+  collectFunctionDeclProps(FD, Unit, Name, LinkageName, DContext,
+                           TParamsArray, Flags);
+  // Build function type.
+  SmallVector<QualType, 16> ArgTypes;
+  for (const ParmVarDecl *Parm: FD->parameters())
+    ArgTypes.push_back(Parm->getType());
+  QualType FnType =
+    CGM.getContext().getFunctionType(FD->getReturnType(), ArgTypes,
+                                     FunctionProtoType::ExtProtoInfo());
+  llvm::DISubprogram SP =
+    DBuilder.createTempFunctionFwdDecl(DContext, Name, LinkageName, Unit, Line,
+                                       getOrCreateFunctionType(FD, FnType, Unit),
+                                       !FD->isExternallyVisible(),
+                                       false /*declaration*/, 0, Flags,
+                                       CGM.getLangOpts().Optimize, nullptr,
+                                       TParamsArray, getFunctionDeclaration(FD));
+  const FunctionDecl *CanonDecl = cast<FunctionDecl>(FD->getCanonicalDecl());
+  FwdDeclReplaceMap.push_back(std::make_pair(CanonDecl,
+                                             static_cast<llvm::Value *>(SP)));
+  return SP;
+}
+
+llvm::DIGlobalVariable
+CGDebugInfo::getGlobalVariableForwardDeclaration(const VarDecl *VD) {
+  QualType T;
+  StringRef Name, LinkageName;
+  SourceLocation Loc = VD->getLocation();
+  llvm::DIFile Unit = getOrCreateFile(Loc);
+  llvm::DIDescriptor DContext(Unit);
+  unsigned Line = getLineNumber(Loc);
+
+  collectVarDeclProps(VD, Unit, Line, T, Name, LinkageName, DContext);
+  llvm::DIGlobalVariable GV =
+    DBuilder.createTempGlobalVariableFwdDecl(DContext, Name, LinkageName, Unit,
+                                             Line, getOrCreateType(T, Unit),
+                                             !VD->isExternallyVisible(),
+                                             nullptr, nullptr);
+  FwdDeclReplaceMap.push_back(std::make_pair(cast<VarDecl>(VD->getCanonicalDecl()),
+                                             static_cast<llvm::Value *>(GV)));
+  return GV;
+}
+
 llvm::DIDescriptor CGDebugInfo::getDeclarationOrDefinition(const Decl *D) {
   // We only need a declaration (not a definition) of the type - so use whatever
   // we would otherwise do to get a type for a pointee. (forward declarations in
   // limited debug info, full definitions (if the type definition is available)
   // in unlimited debug info)
   if (const TypeDecl *TD = dyn_cast<TypeDecl>(D))
     return getOrCreateType(CGM.getContext().getTypeDeclType(TD),
                            getOrCreateFile(TD->getLocation()));
-  // Otherwise fall back to a fairly rudimentary cache of existing declarations.
-  // This doesn't handle providing declarations (for functions or variables) for
-  // entities without definitions in this TU, nor when the definition proceeds
-  // the call to this function.
-  // FIXME: This should be split out into more specific maps with support for
-  // emitting forward declarations and merging definitions with declarations,
-  // the same way as we do for types.
   llvm::DenseMap<const Decl *, llvm::WeakVH>::iterator I =
       DeclCache.find(D->getCanonicalDecl());
-  if (I == DeclCache.end())
-    return llvm::DIScope();
+
+  if (I != DeclCache.end()) {
     llvm::Value *V = I->second;
     return llvm::DIDescriptor(dyn_cast_or_null<llvm::MDNode>(V));
   }
 
+  // No definition for now. Emit a forward definition that might be
+  // merged with a potential upcoming definition.
+  if (const FunctionDecl *FD = dyn_cast_or_null<FunctionDecl>(D))
+    return getFunctionForwardDeclaration(FD);
+  else if (const auto *VD = dyn_cast<VarDecl>(D))
+    return getGlobalVariableForwardDeclaration(VD);
+
+  return llvm::DIDescriptor();
+}
+
 /// getFunctionDeclaration - Return debug info descriptor to describe method
 /// declaration for the given method definition.
 llvm::DISubprogram CGDebugInfo::getFunctionDeclaration(const Decl *D) {
   if (!D || DebugKind <= CodeGenOptions::DebugLineTablesOnly)
     return llvm::DISubprogram();
 
   const FunctionDecl *FD = dyn_cast<FunctionDecl>(D);
   if (!FD)
for (auto p : ReplaceMap) {
     auto it = TypeCache.find(p.first);
     assert(it != TypeCache.end());
     assert(it->second);
 
     llvm::DIType RepTy(cast<llvm::MDNode>(it->second));
     Ty.replaceAllUsesWith(CGM.getLLVMContext(), RepTy);
   }
 
+  for (const auto &p : FwdDeclReplaceMap) {
+    assert(p.second);
+    llvm::DIDescriptor FwdDecl(cast<llvm::MDNode>(p.second));
+    llvm::WeakVH VH;
+
+    auto it = DeclCache.find(p.first);
+    // If there has been no definition for the declaration, call RAUV
+    // with ourselves, that will destroy the temporary MDNode and
+    // replace it with a standard one, avoiding leaking memory.
+    if (it == DeclCache.end())
+      VH = p.second;
+    else
+      VH = it->second;
+    FwdDecl.replaceAllUsesWith(CGM.getLLVMContext(),
+                               llvm::DIDescriptor(cast<llvm::MDNode>(VH)));
+  }
+
   // We keep our own list of retained types, because we need to look
   // up the final type in the type cache.
   for (std::vector<void *>::const_iterator RI = RetainedTypes.begin(),
          RE = RetainedTypes.end(); RI != RE; ++RI)
     DBuilder.retainType(llvm::DIType(cast<llvm::MDNode>(TypeCache[*RI])));
 
   DBuilder.finalize();
 }
 
 void CGDebugInfo::EmitExplicitCastType(QualType Ty) {
   if (CGM.getCodeGenOpts().getDebugInfo() < CodeGenOptions::LimitedDebugInfo)
     return;
   llvm::DIType DieTy = getOrCreateType(Ty, getOrCreateMainFile());
   // Don't ignore in case of explicit cast where it is referenced indirectly.
   DBuilder.retainType(DieTy);
 }

cfe/trunk/test/CodeGenCXX/debug-info-namespace.cpp

 // RUN: %clang_cc1 -g -fno-standalone-debug -S -emit-llvm %s -o - | FileCheck %s
 // RUN: %clang_cc1 -g -gline-tables-only    -S -emit-llvm %s -o - | FileCheck -check-prefix=CHECK-GMLT %s
 // RUN: %clang_cc1 -g -fstandalone-debug    -S -emit-llvm %s -o - | FileCheck -check-prefix=CHECK-NOLIMIT %s
 
 namespace A {
 #line 1 "foo.cpp"
 namespace B {
 extern int i;
 int f1() { return 0; }
 void f1(int) { }
 struct foo;
 struct bar { };
 typedef bar baz;
+extern int var_decl;
+void func_decl(void);
+extern int var_fwd;
+void func_fwd(void);
 }
 }
 namespace A {
 using namespace B;
 }
 
 using namespace A;
 namespace E = A;
 int B::i = f1();
 int func(bool b) {
   if (b) {
     using namespace A::B;
     return i;
   }
   using namespace A;
   using B::foo;
   using B::bar;
   using B::f1;
   using B::i;
   using B::baz;
   namespace X = A;
   namespace Y = X;
+  using B::var_decl;
+  using B::func_decl;
+  using B::var_fwd;
+  using B::func_fwd;
   return i + X::B::i + Y::B::i;
 }
 
 namespace A {
 using B::i;
+namespace B {
+int var_fwd = i;
+}
 }
+void B::func_fwd() {}
 
 // This should work even if 'i' and 'func' were declarations & not definitions,
 // but it doesn't yet.
 
 // CHECK: [[CU:![0-9]*]] = metadata !{metadata !"0x11\00{{.*}}\001"{{.*}}, metadata [[MODULES:![0-9]*]]} ; [ DW_TAG_compile_unit ]
 // CHECK: [[FOO:![0-9]*]] {{.*}} ; [ DW_TAG_structure_type ] [foo] [line 5, size 0, align 0, offset 0] [decl] [from ]
 // CHECK: [[FOOCPP:![0-9]*]] = metadata !{metadata !"foo.cpp", {{.*}}
 // CHECK: [[NS:![0-9]*]] = metadata !{metadata !"0x39\00B\001", metadata [[FILE2:![0-9]*]], metadata [[CTXT:![0-9]*]]} ; [ DW_TAG_namespace ] [B] [line 1]
 // CHECK: [[CTXT]] = metadata !{metadata !"0x39\00A\005", metadata [[FILE:![0-9]*]], null} ; [ DW_TAG_namespace ] [A] [line 5]
 // CHECK: [[FILE]] {{.*}}debug-info-namespace.cpp"
 // CHECK: [[BAR:![0-9]*]] {{.*}} ; [ DW_TAG_structure_type ] [bar] [line 6, {{.*}}] [decl] [from ]
 // CHECK: [[F1:![0-9]*]] {{.*}} ; [ DW_TAG_subprogram ] [line 4] [def] [f1]
 // CHECK: [[FILE2]]} ; [ DW_TAG_file_type ] [{{.*}}foo.cpp]
 // CHECK: [[FUNC:![0-9]*]] {{.*}} ; [ DW_TAG_subprogram ] {{.*}} [def] [func]
+// CHECK: [[FUNC_FWD:![0-9]*]] {{.*}} [ DW_TAG_subprogram ] [line 47] [def] [func_fwd]
 // CHECK: [[I:![0-9]*]] = metadata !{metadata !"0x34\00i\00{{.*}}", metadata [[NS]], {{.*}} ; [ DW_TAG_variable ] [i]
-// CHECK: [[MODULES]] = metadata !{metadata [[M1:![0-9]*]], metadata [[M2:![0-9]*]], metadata [[M3:![0-9]*]], metadata [[M4:![0-9]*]], metadata [[M5:![0-9]*]], metadata [[M6:![0-9]*]], metadata [[M7:![0-9]*]], metadata [[M8:![0-9]*]], metadata [[M9:![0-9]*]], metadata [[M10:![0-9]*]], metadata [[M11:![0-9]*]], metadata [[M12:![0-9]*]], metadata [[M13:![0-9]*]]}
-// CHECK: [[M1]] = metadata !{metadata !"0x3a\0011\00", metadata [[CTXT]], metadata [[NS]]} ; [ DW_TAG_imported_module ]
+// CHECK: [[VAR_FWD:![0-9]*]] = metadata !{metadata !"0x34\00var_fwd\00{{.*}}", metadata [[NS]], {{.*}}} ; [ DW_TAG_variable ] [var_fwd] [line 44] [def]
+
+// CHECK: [[MODULES]] = metadata !{metadata [[M1:![0-9]*]], metadata [[M2:![0-9]*]], metadata [[M3:![0-9]*]], metadata [[M4:![0-9]*]], metadata [[M5:![0-9]*]], metadata [[M6:![0-9]*]], metadata [[M7:![0-9]*]], metadata [[M8:![0-9]*]], metadata [[M9:![0-9]*]], metadata [[M10:![0-9]*]], metadata [[M11:![0-9]*]], metadata [[M12:![0-9]*]], metadata [[M13:![0-9]*]], metadata [[M14:![0-9]*]], metadata [[M15:![0-9]*]], metadata [[M16:![0-9]*]], metadata [[M17:![0-9]*]]}
+// CHECK: [[M1]] = metadata !{metadata !"0x3a\0015\00", metadata [[CTXT]], metadata [[NS]]} ; [ DW_TAG_imported_module ]
 // CHECK: [[M2]] = metadata !{metadata !"0x3a\00{{[0-9]+}}\00", metadata [[CU]], metadata [[CTXT]]} ; [ DW_TAG_imported_module ]
-// CHECK: [[M3]] = metadata !{metadata !"0x8\0015\00E", metadata [[CU]], metadata [[CTXT]]} ; [ DW_TAG_imported_declaration ]
-// CHECK: [[M4]] = metadata !{metadata !"0x3a\0019\00", metadata [[LEX2:![0-9]*]], metadata [[NS]]} ; [ DW_TAG_imported_module ]
+// CHECK: [[M3]] = metadata !{metadata !"0x8\0019\00E", metadata [[CU]], metadata [[CTXT]]} ; [ DW_TAG_imported_declaration ]
+// CHECK: [[M4]] = metadata !{metadata !"0x3a\0023\00", metadata [[LEX2:![0-9]*]], metadata [[NS]]} ; [ DW_TAG_imported_module ]
 // CHECK: [[LEX2]] = metadata !{metadata !"0xb\00{{[0-9]*}}\000\00{{.*}}", metadata [[FILE2]], metadata [[LEX1:![0-9]+]]} ; [ DW_TAG_lexical_block ]
 // CHECK: [[LEX1]] = metadata !{metadata !"0xb\00{{[0-9]*}}\000\00{{.*}}", metadata [[FILE2]], metadata [[FUNC]]} ; [ DW_TAG_lexical_block ]
 // CHECK: [[M5]] = metadata !{metadata !"0x3a\00{{[0-9]+}}\00", metadata [[FUNC]], metadata [[CTXT]]} ; [ DW_TAG_imported_module ]
-// CHECK: [[M6]] = metadata !{metadata !"0x8\0023\00", metadata [[FUNC]], metadata [[FOO:!"_ZTSN1A1B3fooE"]]} ; [ DW_TAG_imported_declaration ]
+// CHECK: [[M6]] = metadata !{metadata !"0x8\0027\00", metadata [[FUNC]], metadata [[FOO:!"_ZTSN1A1B3fooE"]]} ; [ DW_TAG_imported_declaration ]
 // CHECK: [[M7]] = metadata !{metadata !"0x8\00{{[0-9]+}}\00", metadata [[FUNC]], metadata [[BAR:!"_ZTSN1A1B3barE"]]} ; [ DW_TAG_imported_declaration ]
 // CHECK: [[M8]] = metadata !{metadata !"0x8\00{{[0-9]+}}\00", metadata [[FUNC]], metadata [[F1]]} ; [ DW_TAG_imported_declaration ]
 // CHECK: [[M9]] = metadata !{metadata !"0x8\00{{[0-9]+}}\00", metadata [[FUNC]], metadata [[I]]} ; [ DW_TAG_imported_declaration ]
 // CHECK: [[M10]] = metadata !{metadata !"0x8\00{{[0-9]+}}\00", metadata [[FUNC]], metadata [[BAZ:![0-9]*]]} ; [ DW_TAG_imported_declaration ]
 // CHECK: [[BAZ]] = metadata !{metadata !"0x16\00baz\00{{.*}}", metadata [[FOOCPP]], metadata [[NS]], metadata !"_ZTSN1A1B3barE"} ; [ DW_TAG_typedef ] [baz] {{.*}} [from _ZTSN1A1B3barE]
 // CHECK: [[M11]] = metadata !{metadata !"0x8\00{{[0-9]+}}\00X", metadata [[FUNC]], metadata [[CTXT]]} ; [ DW_TAG_imported_declaration ]
 // CHECK: [[M12]] = metadata !{metadata !"0x8\00{{[0-9]+}}\00Y", metadata [[FUNC]], metadata [[M11]]} ; [ DW_TAG_imported_declaration ]
-// CHECK: [[M13]] = metadata !{metadata !"0x8\00{{[0-9]+}}\00", metadata [[CTXT]], metadata [[I]]} ; [ DW_TAG_imported_declaration ]
-
+// CHECK: [[M13]] = metadata !{metadata !"0x8\00{{[0-9]+}}\00", metadata [[FUNC]], metadata [[VAR_DECL:![0-9]*]]} ; [ DW_TAG_imported_declaration ]
+// CHECK [[VAR_DECL]] = metadata !{metadata !"0x34\00var_decl\00{{.*}}", metadata [[NS]], {{.*}}} ; [ DW_TAG_variable ] [var_decl] [line 8]
+// CHECK: [[M14]] = metadata !{metadata !"0x8\00{{[0-9]+}}\00", metadata [[FUNC]], metadata [[FUNC_DECL:![0-9]*]]} ; [ DW_TAG_imported_declaration ]
+// CHECK: [[FUNC_DECL]] = metadata !{metadata !"0x2e\00func_decl\00{{.*}}", metadata [[FOOCPP]], metadata [[NS]], {{.*}}} ; [ DW_TAG_subprogram ] [line 9] [scope 0] [func_decl]
+// CHECK: [[M15]] = metadata !{metadata !"0x8\00{{[0-9]+}}\00", metadata [[FUNC]], metadata [[VAR_FWD:![0-9]*]]} ; [ DW_TAG_imported_declaration ]
+// CHECK: [[M16]] = metadata !{metadata !"0x8\00{{[0-9]+}}\00", metadata [[FUNC]], metadata [[FUNC_FWD:![0-9]*]]} ; [ DW_TAG_imported_declaration ]
+// CHECK: [[M17]] = metadata !{metadata !"0x8\00{{[0-9]+}}\00", metadata [[CTXT]], metadata [[I]]} ; [ DW_TAG_imported_declaration ]
 // CHECK-GMLT: [[CU:![0-9]*]] = metadata !{metadata !"0x11\00{{.*}}\002"{{.*}}, metadata [[MODULES:![0-9]*]]} ; [ DW_TAG_compile_unit ]
 // CHECK-GMLT: [[MODULES]] = metadata !{}
 
 // CHECK-NOLIMIT: ; [ DW_TAG_structure_type ] [bar] [line 6, {{.*}}] [def] [from ]
 
 // REQUIRES: shell-preserves-root
 // REQUIRES: dw2