[mangle] Fix mangling where an extra mangle context is required.

[hliao]

Summary

• [Itanium C++ ABI][1], for certain contexts like default parameter and etc., mangling numbering will be local to the particular argument in which it appears.
• However, for these cases, the mangle numbering context is allocated per expression evaluation stack entry. That causes, for example, two lambdas defined/used understand the same default parameter are numbered as the same value and, in turn, one of them is not generated at all.
• In this patch, an extra mangle numbering context map is maintained in the AST context to map taht extra declaration context to its numbering context. So that, 2 different lambdas defined/used in the same default parameter are numbered differently.
• Minor coding change to perfer using tuple for multiple return values.

[1]: https://itanium-cxx-abi.github.io/cxx-abi/abi.html

[efriedma]

The refactoring of the getCurrentMangleNumberContext API mixed with functional changes makes this much harder to review quickly. Please separate it out.

clang/lib/Sema/SemaLambda.cpp

358

If I'm following correctly, the core of the change is right here? Instead of grabbing a context from the ExpressionEvaluationContextRecord directly, we instead grab the current decl from it, and look up the context from that? That makes sense.

[hliao]

remove refactoring code

[hliao]

clang/lib/Sema/SemaLambda.cpp

358

yeah, that's the code fix. Lots of changes are due to removing unused code due to this change.

[hliao]

s/code/core/ in last comment

[efriedma]

LGTM

[hliao]

In D68715#1701986, @efriedma wrote:

LGTM

Thanks. BTW, shall I commit the refactoring code directly. That change just replaces the code returning multiple values from pointer/reference argument with a tuple.

clang/include/clang/AST/ASTContext.h

private:
   using CXXMethodVector = llvm::TinyPtrVector<const CXXMethodDecl *>;
   llvm::DenseMap<const CXXMethodDecl *, CXXMethodVector> OverriddenMethods;
 
   /// Mapping from each declaration context to its corresponding
   /// mangling numbering context (used for constructs like lambdas which
   /// need to be consistently numbered for the mangler).
   llvm::DenseMap<const DeclContext *, std::unique_ptr<MangleNumberingContext>>
       MangleNumberingContexts;
+  llvm::DenseMap<const Decl *, std::unique_ptr<MangleNumberingContext>>
+      ExtraMangleNumberingContexts;
 
   /// Side-table of mangling numbers for declarations which rarely
   /// need them (like static local vars).
   llvm::MapVector<const NamedDecl *, unsigned> MangleNumbers;
   llvm::MapVector<const VarDecl *, unsigned> StaticLocalNumbers;
 
   /// Mapping that stores parameterIndex values for ParmVarDecls when
   /// that value exceeds the bitfield size of ParmVarDeclBits.ParameterIndex.
public:
   unsigned getManglingNumber(const NamedDecl *ND) const;
 
   void setStaticLocalNumber(const VarDecl *VD, unsigned Number);
   unsigned getStaticLocalNumber(const VarDecl *VD) const;
 
   /// Retrieve the context for computing mangling numbers in the given
   /// DeclContext.
   MangleNumberingContext &getManglingNumberContext(const DeclContext *DC);
+  enum NeedExtraManglingDecl_t { NeedExtraManglingDecl };
+  MangleNumberingContext &getManglingNumberContext(NeedExtraManglingDecl_t,
+                                                   const Decl *D);
 
   std::unique_ptr<MangleNumberingContext> createMangleNumberingContext() const;
 
   /// Used by ParmVarDecl to store on the side the
   /// index of the parameter when it exceeds the size of the normal bitfield.
   void setParameterIndex(const ParmVarDecl *D, unsigned index);
 
   /// Used by ParmVarDecl to retrieve on the side the

clang/include/clang/Sema/Sema.h

struct ExpressionEvaluationContextRecord {
     /// is indeed an unevaluated context.
     SmallVector<LambdaExpr *, 2> Lambdas;
 
     /// The declaration that provides context for lambda expressions
     /// and block literals if the normal declaration context does not
     /// suffice, e.g., in a default function argument.
     Decl *ManglingContextDecl;
 
-    /// The context information used to mangle lambda expressions
-    /// and block literals within this context.
-    ///
-    /// This mangling information is allocated lazily, since most contexts
-    /// do not have lambda expressions or block literals.
-    std::unique_ptr<MangleNumberingContext> MangleNumbering;
-
     /// If we are processing a decltype type, a set of call expressions
     /// for which we have deferred checking the completeness of the return type.
     SmallVector<CallExpr *, 8> DelayedDecltypeCalls;
 
     /// If we are processing a decltype type, a set of temporary binding
     /// expressions for which we have deferred checking the destructor.
     SmallVector<CXXBindTemporaryExpr *, 8> DelayedDecltypeBinds;
 
struct ExpressionEvaluationContextRecord {
 
     ExpressionEvaluationContextRecord(ExpressionEvaluationContext Context,
                                       unsigned NumCleanupObjects,
                                       CleanupInfo ParentCleanup,
                                       Decl *ManglingContextDecl,
                                       ExpressionKind ExprContext)
         : Context(Context), ParentCleanup(ParentCleanup),
           NumCleanupObjects(NumCleanupObjects), NumTypos(0),
-          ManglingContextDecl(ManglingContextDecl), MangleNumbering(),
-          ExprContext(ExprContext) {}
-
-    /// Retrieve the mangling numbering context, used to consistently
-    /// number constructs like lambdas for mangling.
-    MangleNumberingContext &getMangleNumberingContext(ASTContext &Ctx);
+          ManglingContextDecl(ManglingContextDecl), ExprContext(ExprContext) {}
 
     bool isUnevaluated() const {
       return Context == ExpressionEvaluationContext::Unevaluated ||
              Context == ExpressionEvaluationContext::UnevaluatedAbstract ||
              Context == ExpressionEvaluationContext::UnevaluatedList;
     }
     bool isConstantEvaluated() const {
       return Context == ExpressionEvaluationContext::ConstantEvaluated;

clang/lib/AST/ASTContext.cpp

 ASTContext::getManglingNumberContext(const DeclContext *DC) {
   assert(LangOpts.CPlusPlus);  // We don't need mangling numbers for plain C.
   std::unique_ptr<MangleNumberingContext> &MCtx = MangleNumberingContexts[DC];
   if (!MCtx)
     MCtx = createMangleNumberingContext();
   return *MCtx;
 }
 
+MangleNumberingContext &
+ASTContext::getManglingNumberContext(NeedExtraManglingDecl_t, const Decl *D) {
+  assert(LangOpts.CPlusPlus); // We don't need mangling numbers for plain C.
+  std::unique_ptr<MangleNumberingContext> &MCtx =
+      ExtraMangleNumberingContexts[D];
+  if (!MCtx)
+    MCtx = createMangleNumberingContext();
+  return *MCtx;
+}
+
 std::unique_ptr<MangleNumberingContext>
 ASTContext::createMangleNumberingContext() const {
   return ABI->createMangleNumberingContext();
 }
 
 const CXXConstructorDecl *
 ASTContext::getCopyConstructorForExceptionObject(CXXRecordDecl *RD) {
   return ABI->getCopyConstructorForExceptionObject(

clang/lib/Sema/SemaLambda.cpp

Sema::getCurrentMangleNumberContext(const DeclContext *DC,
   case DataMember:
     //  -- the in-class initializers of class members
   case DefaultArgument:
     //  -- default arguments appearing in class definitions
   case InlineVariable:
     //  -- the initializers of inline variables
   case VariableTemplate:
     //  -- the initializers of templated variables
-    return &ExprEvalContexts.back().getMangleNumberingContext(Context);
+    return &Context.getManglingNumberContext(ASTContext::NeedExtraManglingDecl,
+                                             ManglingContextDecl);
   }
 
   llvm_unreachable("unexpected context");
 }
 
-MangleNumberingContext &
-Sema::ExpressionEvaluationContextRecord::getMangleNumberingContext(
-    ASTContext &Ctx) {
-  assert(ManglingContextDecl && "Need to have a context declaration");
-  if (!MangleNumbering)
-    MangleNumbering = Ctx.createMangleNumberingContext();
-  return *MangleNumbering;
-}
-
 CXXMethodDecl *Sema::startLambdaDefinition(
     CXXRecordDecl *Class, SourceRange IntroducerRange,
     TypeSourceInfo *MethodTypeInfo, SourceLocation EndLoc,
     ArrayRef<ParmVarDecl *> Params, ConstexprSpecKind ConstexprKind,
     Optional<std::pair<unsigned, Decl *>> Mangling) {
   QualType MethodType = MethodTypeInfo->getType();
   TemplateParameterList *TemplateParams =
             getGenericLambdaTemplateParameterList(getCurLambda(), *this);

clang/test/CodeGenCXX/mangle-lambdas.cpp

 
 // CHECK-LABEL: define void @_Z17use_func_templatev()
 void use_func_template() {
   // CHECK: call i32 @"_ZZ13func_templateIiEvT_ENK3$_3clEv"
   func_template<int>();
 }
 
 namespace std {
-  struct type_info;
+  struct type_info {
+    bool before(const type_info &) const noexcept;
+  };
 }
 namespace PR12123 {
   struct A { virtual ~A(); } g;
+  struct C { virtual ~C(); } k;
   struct B {
     void f(const std::type_info& x = typeid([]()->A& { return g; }()));
     void h();
+    void j(bool cond = typeid([]() -> A & { return g; }()).before(typeid([]() -> C & { return k; }())));
   };
-  void B::h() { f(); }
+  void B::h() { f(); j(); }
 }
 
 // CHECK-LABEL: define linkonce_odr dereferenceable({{[0-9]+}}) %"struct.PR12123::A"* @_ZZN7PR121231B1fERKSt9type_infoEd_NKUlvE_clEv
+// CHECK-LABEL: define linkonce_odr dereferenceable({{[0-9]+}}) %"struct.PR12123::A"* @_ZZN7PR121231B1jEbEd_NKUlvE_clEv
+// CHECK-LABEL: define linkonce_odr dereferenceable({{[0-9]+}}) %"struct.PR12123::C"* @_ZZN7PR121231B1jEbEd_NKUlvE0_clEv
 
 // CHECK-LABEL: define {{.*}} @_Z{{[0-9]*}}testVarargsLambdaNumberingv(
 inline int testVarargsLambdaNumbering() {
   // CHECK: testVarargsLambdaNumberingvE{{.*}}UlzE_
   auto a = [](...) { static int n; return ++n; };
   // CHECK: testVarargsLambdaNumberingvE{{.*}}UlvE_
   auto b = []() { static int n; return ++n; };
   return a() + b();