[Clang] implement -fno-eliminate-unused-debug-types

Fixes pr/11710.
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>

Reviewed By: dblaikie

Differential Revision: https://reviews.llvm.org/D80242

clang/docs/ClangCommandLineReference.rst

@@ -2154,6 +2154,10 @@ Emit section containing metadata on function stack sizes
 
 Emit full debug info for all types used by the program
 
+.. option:: -feliminate-unused-debug-types, -fno-eliminate-unused-debug-types
+
+Suppress (or emit) debug info for types that are unused but defined by the program.
+
 .. option:: -fstrict-aliasing, -fno-strict-aliasing
 
 .. option:: -fstrict-enums, -fno-strict-enums

clang/docs/CommandGuide/clang.rst

@@ -433,6 +433,12 @@ Code Generation Options
   never emit type information for types that are not referenced at all by the
   program.
 
+.. option:: -feliminate-unused-debug-types
+
+  By default, Clang does not emit type information for types that are defined
+  but not used in a program. To retain the debug info for these unused types,
+  the negation **-fno-eliminate-unused-debug-types** can be used.
+
 .. option:: -fexceptions
 
   Enable generation of unwind information. This allows exceptions to be thrown

clang/docs/UsersManual.rst

@@ -2352,6 +2352,12 @@ below. If multiple flags are present, the last one is used.
 
   Generate complete debug info.
 
+.. option:: -feliminate-unused-debug-types
+
+  By default, Clang does not emit type information for types that are defined
+  but not used in a program. To retain the debug info for these unused types,
+  the negation **-fno-eliminate-unused-debug-types** can be used.
+
 Controlling Macro Debug Info Generation
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 

clang/include/clang/Basic/CodeGenOptions.def

@@ -288,7 +288,6 @@ CODEGENOPT(DebugFwdTemplateParams, 1, 0) ///< Whether to emit complete
                                          ///< template parameter descriptions in
                                          ///< forward declarations (versus just
                                          ///< including them in the name).
-
 CODEGENOPT(EmitLLVMUseLists, 1, 0) ///< Control whether to serialize use-lists.
 
 CODEGENOPT(WholeProgramVTables, 1, 0) ///< Whether to apply whole-program
@@ -313,7 +312,7 @@ VALUE_CODEGENOPT(SmallDataLimit, 32, 0)
 VALUE_CODEGENOPT(SSPBufferSize, 32, 0)
 
 /// The kind of generated debug info.
-ENUM_CODEGENOPT(DebugInfo, codegenoptions::DebugInfoKind, 3, codegenoptions::NoDebugInfo)
+ENUM_CODEGENOPT(DebugInfo, codegenoptions::DebugInfoKind, 4, codegenoptions::NoDebugInfo)
 
 /// Whether to generate macro debug info.
 CODEGENOPT(MacroDebugInfo, 1, 0)

clang/include/clang/Basic/CodeGenOptions.h

@@ -388,6 +388,11 @@ public:
   bool hasReducedDebugInfo() const {
     return getDebugInfo() >= codegenoptions::DebugInfoConstructor;
   }
+
+  /// Check if maybe unused type info should be emitted.
+  bool hasMaybeUnusedDebugInfo() const {
+    return getDebugInfo() >= codegenoptions::UnusedTypeInfo;
+  }
 };
 
 }  // end namespace clang

clang/include/clang/Basic/DebugInfoOptions.h

@@ -46,7 +46,11 @@ enum DebugInfoKind {
   LimitedDebugInfo,
 
   /// Generate complete debug info.
-  FullDebugInfo
+  FullDebugInfo,
+
+  /// Generate debug info for types that may be unused in the source
+  /// (-fno-eliminate-unused-debug-types).
+  UnusedTypeInfo,
 };
 
 } // end namespace codegenoptions

clang/include/clang/Driver/Options.td

@@ -943,6 +943,8 @@ def fno_elide_type : Flag<["-"], "fno-elide-type">, Group<f_Group>,
     Flags<[CC1Option]>,
     HelpText<"Do not elide types when printing diagnostics">;
 def feliminate_unused_debug_symbols : Flag<["-"], "feliminate-unused-debug-symbols">, Group<f_Group>;
+defm eliminate_unused_debug_types : OptOutFFlag<"eliminate-unused-debug-types",
+  "Do not emit ", "Emit ", " debug info for defined but unused types">;
 def femit_all_decls : Flag<["-"], "femit-all-decls">, Group<f_Group>, Flags<[CC1Option]>,
   HelpText<"Emit all declarations, even if unused">;
 def femulated_tls : Flag<["-"], "femulated-tls">, Group<f_Group>, Flags<[CC1Option]>,
@@ -3321,7 +3323,6 @@ def fdiagnostics_show_location_EQ : Joined<["-"], "fdiagnostics-show-location=">
 defm fcheck_new : BooleanFFlag<"check-new">, Group<clang_ignored_f_Group>;
 defm caller_saves : BooleanFFlag<"caller-saves">, Group<clang_ignored_gcc_optimization_f_Group>;
 defm reorder_blocks : BooleanFFlag<"reorder-blocks">, Group<clang_ignored_gcc_optimization_f_Group>;
-defm eliminate_unused_debug_types : BooleanFFlag<"eliminate-unused-debug-types">, Group<clang_ignored_f_Group>;
 defm branch_count_reg : BooleanFFlag<"branch-count-reg">, Group<clang_ignored_gcc_optimization_f_Group>;
 defm default_inline : BooleanFFlag<"default-inline">, Group<clang_ignored_gcc_optimization_f_Group>;
 defm fat_lto_objects : BooleanFFlag<"fat-lto-objects">, Group<clang_ignored_gcc_optimization_f_Group>;

clang/lib/CodeGen/CGDebugInfo.cpp

@@ -606,6 +606,7 @@ void CGDebugInfo::CreateCompileUnit() {
   case codegenoptions::DebugInfoConstructor:
   case codegenoptions::LimitedDebugInfo:
   case codegenoptions::FullDebugInfo:
+  case codegenoptions::UnusedTypeInfo:
     EmissionKind = llvm::DICompileUnit::FullDebug;
     break;
   }
@@ -4960,12 +4961,16 @@ void CGDebugInfo::finalize() {
   DBuilder.finalize();
 }
 
+// Don't ignore in case of explicit cast where it is referenced indirectly.
 void CGDebugInfo::EmitExplicitCastType(QualType Ty) {
-  if (!CGM.getCodeGenOpts().hasReducedDebugInfo())
-    return;
-
+  if (CGM.getCodeGenOpts().hasReducedDebugInfo())
+    if (auto *DieTy = getOrCreateType(Ty, TheCU->getFile()))
+      DBuilder.retainType(DieTy);
+}
+
+void CGDebugInfo::EmitAndRetainType(QualType Ty) {
+  if (CGM.getCodeGenOpts().hasMaybeUnusedDebugInfo())
     if (auto *DieTy = getOrCreateType(Ty, TheCU->getFile()))
-    // Don't ignore in case of explicit cast where it is referenced indirectly.
       DBuilder.retainType(DieTy);
 }
 

clang/lib/CodeGen/CGDebugInfo.h

@@ -490,6 +490,9 @@ public:
   /// Emit the type explicitly casted to.
   void EmitExplicitCastType(QualType Ty);
 
+  /// Emit the type even if it might not be used.
+  void EmitAndRetainType(QualType Ty);
+
   /// Emit C++ using declaration.
   void EmitUsingDecl(const UsingDecl &UD);
 

clang/lib/CodeGen/CGDecl.cpp

@@ -100,11 +100,19 @@ void CodeGenFunction::EmitDecl(const Decl &D) {
   case Decl::ObjCTypeParam:
   case Decl::Binding:
     llvm_unreachable("Declaration should not be in declstmts!");
-  case Decl::Function:  // void X();
   case Decl::Record:    // struct/union/class X;
-  case Decl::Enum:      // enum X;
-  case Decl::EnumConstant: // enum ? { X = ? }
   case Decl::CXXRecord: // struct/union/class X; [C++]
+    if (CGDebugInfo *DI = getDebugInfo())
+      if (cast<RecordDecl>(D).getDefinition())
+        DI->EmitAndRetainType(getContext().getRecordType(cast<RecordDecl>(&D)));
+    return;
+  case Decl::Enum:      // enum X;
+    if (CGDebugInfo *DI = getDebugInfo())
+      if (cast<EnumDecl>(D).getDefinition())
+        DI->EmitAndRetainType(getContext().getEnumType(cast<EnumDecl>(&D)));
+    return;
+  case Decl::Function:     // void X();
+  case Decl::EnumConstant: // enum ? { X = ? }
   case Decl::StaticAssert: // static_assert(X, ""); [C++0x]
   case Decl::Label:        // __label__ x;
   case Decl::Import:
@@ -157,12 +165,11 @@ void CodeGenFunction::EmitDecl(const Decl &D) {
 
   case Decl::Typedef:      // typedef int X;
   case Decl::TypeAlias: {  // using X = int; [C++0x]
-    const TypedefNameDecl &TD = cast<TypedefNameDecl>(D);
-    QualType Ty = TD.getUnderlyingType();
-
+    QualType Ty = cast<TypedefNameDecl>(D).getUnderlyingType();
+    if (CGDebugInfo *DI = getDebugInfo())
+      DI->EmitAndRetainType(Ty);
     if (Ty->isVariablyModifiedType())
       EmitVariablyModifiedType(Ty);
-
     return;
   }
   }

clang/lib/CodeGen/CodeGenModule.cpp

@@ -5392,16 +5392,21 @@ void CodeGenModule::EmitTopLevelDecl(Decl *D) {
           Spec->hasDefinition())
         DI->completeTemplateDefinition(*Spec);
   } LLVM_FALLTHROUGH;
-  case Decl::CXXRecord:
-    if (CGDebugInfo *DI = getModuleDebugInfo())
+  case Decl::CXXRecord: {
+    CXXRecordDecl *CRD = cast<CXXRecordDecl>(D);
+    if (CGDebugInfo *DI = getModuleDebugInfo()) {
+      if (CRD->hasDefinition())
+        DI->EmitAndRetainType(getContext().getRecordType(cast<RecordDecl>(D)));
       if (auto *ES = D->getASTContext().getExternalSource())
         if (ES->hasExternalDefinitions(D) == ExternalASTSource::EK_Never)
-          DI->completeUnusedClass(cast<CXXRecordDecl>(*D));
+          DI->completeUnusedClass(*CRD);
+    }
     // Emit any static data members, they may be definitions.
-    for (auto *I : cast<CXXRecordDecl>(D)->decls())
+    for (auto *I : CRD->decls())
       if (isa<VarDecl>(I) || isa<CXXRecordDecl>(I))
         EmitTopLevelDecl(I);
     break;
+  }
     // No code generation needed.
   case Decl::UsingShadow:
   case Decl::ClassTemplate:
@@ -5587,6 +5592,25 @@ void CodeGenModule::EmitTopLevelDecl(Decl *D) {
     EmitOMPRequiresDecl(cast<OMPRequiresDecl>(D));
     break;
 
+  case Decl::Typedef:
+  case Decl::TypeAlias: // using foo = bar; [C++11]
+    if (CGDebugInfo *DI = getModuleDebugInfo())
+      DI->EmitAndRetainType(
+          getContext().getTypedefType(cast<TypedefNameDecl>(D)));
+    break;
+
+  case Decl::Record:
+    if (CGDebugInfo *DI = getModuleDebugInfo())
+      if (cast<RecordDecl>(D)->getDefinition())
+        DI->EmitAndRetainType(getContext().getRecordType(cast<RecordDecl>(D)));
+    break;
+
+  case Decl::Enum:
+    if (CGDebugInfo *DI = getModuleDebugInfo())
+      if (cast<EnumDecl>(D)->getDefinition())
+        DI->EmitAndRetainType(getContext().getEnumType(cast<EnumDecl>(D)));
+    break;
+
   default:
     // Make sure we handled everything we should, every other kind is a
     // non-top-level decl.  FIXME: Would be nice to have an isTopLevelDeclKind

clang/lib/Driver/ToolChains/Clang.cpp

@@ -976,6 +976,9 @@ static void RenderDebugEnablingArgs(const ArgList &Args, ArgStringList &CmdArgs,
   case codegenoptions::FullDebugInfo:
     CmdArgs.push_back("-debug-info-kind=standalone");
     break;
+  case codegenoptions::UnusedTypeInfo:
+    CmdArgs.push_back("-debug-info-kind=unused-types");
+    break;
   default:
     break;
   }
@@ -3781,8 +3784,14 @@ static void RenderDebugOptions(const ToolChain &TC, const Driver &D,
           TC.GetDefaultStandaloneDebug());
   if (const Arg *A = Args.getLastArg(options::OPT_fstandalone_debug))
     (void)checkDebugInfoOption(A, Args, D, TC);
-  if (DebugInfoKind == codegenoptions::LimitedDebugInfo && NeedFullDebug)
+
+  if (DebugInfoKind == codegenoptions::LimitedDebugInfo) {
+    if (Args.hasFlag(options::OPT_fno_eliminate_unused_debug_types,
+                     options::OPT_feliminate_unused_debug_types, false))
+      DebugInfoKind = codegenoptions::UnusedTypeInfo;
+    else if (NeedFullDebug)
       DebugInfoKind = codegenoptions::FullDebugInfo;
+  }
 
   if (Args.hasFlag(options::OPT_gembed_source, options::OPT_gno_embed_source,
                    false)) {

clang/lib/Frontend/CompilerInvocation.cpp

@@ -767,6 +767,7 @@ static bool ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args, InputKind IK,
             .Case("constructor", codegenoptions::DebugInfoConstructor)
             .Case("limited", codegenoptions::LimitedDebugInfo)
             .Case("standalone", codegenoptions::FullDebugInfo)
+            .Case("unused-types", codegenoptions::UnusedTypeInfo)
             .Default(~0U);
     if (Val == ~0U)
       Diags.Report(diag::err_drv_invalid_value) << A->getAsString(Args)

clang/test/CodeGen/debug-info-unused-types.c

@@ -0,0 +1,50 @@
+// RUN: %clang -fno-eliminate-unused-debug-types -g -emit-llvm -S -o - %s | FileCheck %s
+// RUN: %clang -fno-eliminate-unused-debug-types -g1 -emit-llvm -S -o - %s | FileCheck --check-prefix=NODBG %s
+// RUN: %clang -feliminate-unused-debug-types -g -emit-llvm -S -o - %s | FileCheck --check-prefix=NODBG %s
+// RUN: %clang -g -emit-llvm -S -o - %s | FileCheck --check-prefix=NODBG %s
+// RUN: %clang -emit-llvm -S -o - %s | FileCheck --check-prefix=NODBG %s
+typedef int my_int;
+struct foo {};
+enum bar { BAR };
+union baz {};
+
+void quux(void) {
+  typedef int x;
+  struct y {};
+  enum z { Z };
+  union w {};
+}
+
+// Check that debug info is emitted for the typedef, struct, enum, and union
+// when -fno-eliminate-unused-debug-types and -g are set.
+
+// CHECK: !DICompileUnit{{.+}}retainedTypes: [[RETTYPES:![0-9]+]]
+// CHECK: [[TYPE0:![0-9]+]] = !DICompositeType(tag: DW_TAG_enumeration_type, name: "bar"
+// CHECK: [[TYPE1:![0-9]+]] = !DIEnumerator(name: "BAR"
+// CHECK: [[TYPE2:![0-9]+]] = !DICompositeType(tag: DW_TAG_enumeration_type, name: "z"
+// CHECK: [[TYPE3:![0-9]+]] = !DIEnumerator(name: "Z"
+// CHECK: [[RETTYPES]] = !{[[TYPE4:![0-9]+]], [[TYPE5:![0-9]+]], [[TYPE0]], [[TYPE6:![0-9]+]], !17, [[TYPE7:![0-9]+]], [[TYPE2]], [[TYPE8:![0-9]+]]}
+// CHECK: [[TYPE4]] = !DIDerivedType(tag: DW_TAG_typedef, name: "my_int"
+// CHECK: [[TYPE5]] = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "foo"
+// CHECK: [[TYPE6]] = distinct !DICompositeType(tag: DW_TAG_union_type, name: "baz"
+// CHECK: [[TYPE7]] = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "y"
+// CHECK: [[TYPE8]] = distinct !DICompositeType(tag: DW_TAG_union_type, name: "w"
+
+// Check that debug info is not emitted for the typedef, struct, enum, and
+// union when -fno-eliminate-unused-debug-types and -g are not set. These are
+// the same checks as above with `NODBG-NOT` rather than `CHECK`.
+
+// NODBG-NOT: !DI{{CompositeType|Enumerator|DerivedType}}
+
+// Check that debug info is not emitted for declarations. Obnoxious
+// indentifiers are to avoid collisions with the SHA emittied as debug info.
+struct unused_struct;
+enum unused_enum;
+union unused_union;
+void b0(void) {
+  struct unused_local_struct;
+  enum unused_local_enum;
+  union unused_local_union;
+}
+
+// NODBG-NOT: name: "unused_

clang/test/CodeGen/debug-info-unused-types.cpp

@@ -0,0 +1,31 @@
+// RUN: %clang++ -fno-eliminate-unused-debug-types -g -emit-llvm -S -o - %s | FileCheck %s
+// RUN: %clang++ -fno-eliminate-unused-debug-types -g1 -emit-llvm -S -o - %s | FileCheck --check-prefix=NODBG %s
+// RUN: %clang++ -feliminate-unused-debug-types -g -emit-llvm -S -o - %s | FileCheck --check-prefix=NODBG %s
+// RUN: %clang++ -g -emit-llvm -S -o - %s | FileCheck --check-prefix=NODBG %s
+// RUN: %clang++ -emit-llvm -S -o - %s | FileCheck --check-prefix=NODBG %s
+using foo = int;
+class bar {};
+enum class baz { BAZ };
+
+void quux() {
+  using x = int;
+  class y {};
+  enum class z { Z };
+}
+
+// CHECK: !DICompileUnit{{.+}}retainedTypes: [[RETTYPES:![0-9]+]]
+// CHECK: [[TYPE0:![0-9]+]] = !DICompositeType(tag: DW_TAG_enumeration_type, name: "baz"
+// CHECK: [[TYPE1:![0-9]+]] = !DIEnumerator(name: "BAZ"
+// CHECK: [[TYPE2:![0-9]+]] = !DICompositeType(tag: DW_TAG_enumeration_type, name: "z"
+// CHECK: [[TYPE3:![0-9]+]] = !DIEnumerator(name: "Z"
+// CHECK: [[RETTYPES]] = !{[[TYPE4:![0-9]+]], [[TYPE5:![0-9]+]], [[TYPE0]], !5, [[TYPE6:![0-9]+]], [[TYPE2]]}
+// CHECK: [[TYPE4]] = !DIDerivedType(tag: DW_TAG_typedef, name: "foo"
+// CHECK: [[TYPE5]] = distinct !DICompositeType(tag: DW_TAG_class_type, name: "bar"
+// CHECK: [[TYPE6]] = distinct !DICompositeType(tag: DW_TAG_class_type, name: "y"
+
+// NODBG-NOT: !DI{{CompositeType|Enumerator|DerivedType}}
+
+class unused_class;
+enum class unused_enum_class;
+
+// NODBG-NOT: name: "unused_

clang/test/Driver/debug-options.c

@@ -361,3 +361,12 @@
 // GEMBED_2:  error: invalid argument '-gembed-source' only allowed with '-gdwarf-5'
 // NOGEMBED_5-NOT:  "-gembed-source"
 // NOGEMBED_2-NOT:  error: invalid argument '-gembed-source' only allowed with '-gdwarf-5'
+//
+// RUN: %clang -### -g -fno-eliminate-unused-debug-types -c %s 2>&1 \
+// RUN:        | FileCheck -check-prefix=DEBUG_UNUSED_TYPES %s
+// DEBUG_UNUSED_TYPES: "-debug-info-kind=unused-types"
+// DEBUG_UNUSED_TYPES-NOT: "-debug-info-kind=limited"
+// RUN: %clang -### -g -feliminate-unused-debug-types -c %s 2>&1 \
+// RUN:        | FileCheck -check-prefix=NO_DEBUG_UNUSED_TYPES %s
+// NO_DEBUG_UNUSED_TYPES: "-debug-info-kind=limited"
+// NO_DEBUG_UNUSED_TYPES-NOT: "-debug-info-kind=unused-types"