Mark identifier prefixes as substitutable

The Itanium C++ ABI says prefixes are substitutable. For most prefixes
we already handle this: the manglePrefix(const DeclContext *, bool) and
manglePrefix(QualType) overloads explicitly handles substitutions or
defer to functions that handle substitutions on their behalf. The
manglePrefix(NestedNameSpecifier *) overload, however, is different and
handles some cases implicitly, but not all. The Identifier case was not
handled; this change adds handling for it, as well as a test case.

Reviewed By: erichkeane

Differential Revision: https://reviews.llvm.org/D122663

clang/docs/ReleaseNotes.rst

@@ -265,6 +265,10 @@ C++ Language Changes in Clang
   ``std::move_if_noexcept``, ``std::addressof``, and ``std::as_const``. These
   are now treated as compiler builtins and implemented directly, rather than
   instantiating the definition from the standard library.
+- Fixed mangling of nested dependent names such as ``T::a::b``, where ``T`` is a
+  template parameter, to conform to the Itanium C++ ABI and be compatible with
+  GCC. This breaks binary compatibility with code compiled with earlier versions
+  of clang; use the ``-fclang-abi-compat=14`` option to get the old mangling.
 
 C++20 Feature Support
 ^^^^^^^^^^^^^^^^^^^^^

clang/include/clang/Basic/LangOptions.h

@@ -218,6 +218,10 @@ public:
     /// This causes clang to not pack non-POD members of packed structs.
     Ver13,
 
+    /// Attempt to be ABI-compatible with code generated by Clang 14.0.x.
+    /// This causes clang to mangle dependent nested names incorrectly.
+    Ver14,
+
     /// Conform to the underlying platform's C and C++ ABIs as closely
     /// as we can.
     Latest

clang/lib/AST/ItaniumMangle.cpp

@@ -443,6 +443,7 @@ public:
 private:
 
   bool mangleSubstitution(const NamedDecl *ND);
+  bool mangleSubstitution(NestedNameSpecifier *NNS);
   bool mangleSubstitution(QualType T);
   bool mangleSubstitution(TemplateName Template);
   bool mangleSubstitution(uintptr_t Ptr);
@@ -456,6 +457,11 @@ private:
 
     addSubstitution(reinterpret_cast<uintptr_t>(ND));
   }
+  void addSubstitution(NestedNameSpecifier *NNS) {
+    NNS = Context.getASTContext().getCanonicalNestedNameSpecifier(NNS);
+
+    addSubstitution(reinterpret_cast<uintptr_t>(NNS));
+  }
   void addSubstitution(QualType T);
   void addSubstitution(TemplateName Template);
   void addSubstitution(uintptr_t Ptr);
@@ -2036,12 +2042,21 @@ void CXXNameMangler::manglePrefix(NestedNameSpecifier *qualifier) {
     return;
 
   case NestedNameSpecifier::Identifier:
+    // Clang 14 and before did not consider this substitutable.
+    bool Clang14Compat = getASTContext().getLangOpts().getClangABICompat() <=
+                         LangOptions::ClangABI::Ver14;
+    if (!Clang14Compat && mangleSubstitution(qualifier))
+      return;
+
     // Member expressions can have these without prefixes, but that
     // should end up in mangleUnresolvedPrefix instead.
     assert(qualifier->getPrefix());
     manglePrefix(qualifier->getPrefix());
 
     mangleSourceName(qualifier->getAsIdentifier());
+
+    if (!Clang14Compat)
+      addSubstitution(qualifier);
     return;
   }
 
@@ -6009,6 +6024,14 @@ bool CXXNameMangler::mangleSubstitution(const NamedDecl *ND) {
   return mangleSubstitution(reinterpret_cast<uintptr_t>(ND));
 }
 
+bool CXXNameMangler::mangleSubstitution(NestedNameSpecifier *NNS) {
+  assert(NNS->getKind() == NestedNameSpecifier::Identifier &&
+         "mangleSubstitution(NestedNameSpecifier *) is only used for "
+         "identifier nested name specifiers.");
+  NNS = Context.getASTContext().getCanonicalNestedNameSpecifier(NNS);
+  return mangleSubstitution(reinterpret_cast<uintptr_t>(NNS));
+}
+
 /// Determine whether the given type has any qualifiers that are relevant for
 /// substitutions.
 static bool hasMangledSubstitutionQualifiers(QualType T) {

clang/lib/Frontend/CompilerInvocation.cpp

@@ -3518,6 +3518,8 @@ void CompilerInvocation::GenerateLangArgs(const LangOptions &Opts,
     GenerateArg(Args, OPT_fclang_abi_compat_EQ, "12.0", SA);
   else if (Opts.getClangABICompat() == LangOptions::ClangABI::Ver13)
     GenerateArg(Args, OPT_fclang_abi_compat_EQ, "13.0", SA);
+  else if (Opts.getClangABICompat() == LangOptions::ClangABI::Ver14)
+    GenerateArg(Args, OPT_fclang_abi_compat_EQ, "14.0", SA);
 
   if (Opts.getSignReturnAddressScope() ==
       LangOptions::SignReturnAddressScopeKind::All)
@@ -4026,6 +4028,8 @@ bool CompilerInvocation::ParseLangArgs(LangOptions &Opts, ArgList &Args,
         Opts.setClangABICompat(LangOptions::ClangABI::Ver12);
       else if (Major <= 13)
         Opts.setClangABICompat(LangOptions::ClangABI::Ver13);
+      else if (Major <= 14)
+        Opts.setClangABICompat(LangOptions::ClangABI::Ver14);
     } else if (Ver != "latest") {
       Diags.Report(diag::err_drv_invalid_value)
           << A->getAsString(Args) << A->getValue();

clang/test/CodeGenCXX/clang-abi-compat.cpp

@@ -1,25 +1,27 @@
 // RUN: %clang_cc1 -no-opaque-pointers -std=c++98 -triple x86_64-linux-gnu -fenable-matrix -fclang-abi-compat=3.0 %s -emit-llvm -o - -Wno-c++11-extensions \
-// RUN:     | FileCheck --check-prefixes=CHECK,PRE39,PRE5,PRE12 %s
+// RUN:     | FileCheck --check-prefixes=CHECK,PRE39,PRE5,PRE12,PRE15 %s
 // RUN: %clang_cc1 -no-opaque-pointers -std=c++17 -triple x86_64-linux-gnu -fenable-matrix -fclang-abi-compat=3.0 %s -emit-llvm -o - \
-// RUN:     | FileCheck --check-prefixes=CHECK,PRE39,PRE5,PRE12 %s
+// RUN:     | FileCheck --check-prefixes=CHECK,PRE39,PRE5,PRE12,PRE15 %s
 // RUN: %clang_cc1 -no-opaque-pointers -std=c++17 -triple x86_64-linux-gnu -fenable-matrix -fclang-abi-compat=3.8 %s -emit-llvm -o - \
-// RUN:     | FileCheck --check-prefixes=CHECK,PRE39,PRE5,PRE12 %s
+// RUN:     | FileCheck --check-prefixes=CHECK,PRE39,PRE5,PRE12,PRE15 %s
 // RUN: %clang_cc1 -no-opaque-pointers -std=c++17 -triple x86_64-linux-gnu -fenable-matrix -fclang-abi-compat=3.9 %s -emit-llvm -o - \
-// RUN:     | FileCheck --check-prefixes=CHECK,V39,PRE5,PRE12 %s
+// RUN:     | FileCheck --check-prefixes=CHECK,V39,PRE5,PRE12,PRE15 %s
 // RUN: %clang_cc1 -no-opaque-pointers -std=c++17 -triple x86_64-linux-gnu -fenable-matrix -fclang-abi-compat=4.0 %s -emit-llvm -o - \
-// RUN:     | FileCheck --check-prefixes=CHECK,V39,PRE5,PRE12 %s
+// RUN:     | FileCheck --check-prefixes=CHECK,V39,PRE5,PRE12,PRE15 %s
 // RUN: %clang_cc1 -no-opaque-pointers -std=c++17 -triple x86_64-linux-gnu -fenable-matrix -fclang-abi-compat=5 %s -emit-llvm -o - \
-// RUN:     | FileCheck --check-prefixes=CHECK,V39,V5,PRE12,PRE12-CXX17 %s
+// RUN:     | FileCheck --check-prefixes=CHECK,V39,V5,PRE12,PRE12-CXX17,PRE15 %s
 // RUN: %clang_cc1 -no-opaque-pointers -std=c++17 -triple x86_64-linux-gnu -fenable-matrix -fclang-abi-compat=11 %s -emit-llvm -o - \
-// RUN:     | FileCheck --check-prefixes=CHECK,V39,V5,PRE12,PRE12-CXX17 %s
+// RUN:     | FileCheck --check-prefixes=CHECK,V39,V5,PRE12,PRE12-CXX17,PRE15 %s
 // RUN: %clang_cc1 -no-opaque-pointers -std=c++20 -triple x86_64-linux-gnu -fenable-matrix -fclang-abi-compat=11 %s -emit-llvm -o - \
-// RUN:     | FileCheck --check-prefixes=CHECK,V39,V5,PRE12,PRE12-CXX17,PRE12-CXX20,PRE13-CXX20 %s
+// RUN:     | FileCheck --check-prefixes=CHECK,V39,V5,PRE12,PRE12-CXX17,PRE12-CXX20,PRE13-CXX20,PRE15 %s
 // RUN: %clang_cc1 -no-opaque-pointers -std=c++20 -triple x86_64-linux-gnu -fenable-matrix -fclang-abi-compat=12 %s -emit-llvm -o - \
-// RUN:     | FileCheck --check-prefixes=CHECK,V39,V5,V12,V12-CXX17,V12-CXX20,PRE13-CXX20 %s
+// RUN:     | FileCheck --check-prefixes=CHECK,V39,V5,V12,V12-CXX17,V12-CXX20,PRE13-CXX20,PRE15 %s
+// RUN: %clang_cc1 -no-opaque-pointers -std=c++20 -triple x86_64-linux-gnu -fenable-matrix -fclang-abi-compat=14 %s -emit-llvm -o - \
+// RUN:     | FileCheck --check-prefixes=CHECK,V39,V5,V12,V12-CXX17,V12-CXX20,V13-CXX20,PRE15 %s
 // RUN: %clang_cc1 -no-opaque-pointers -std=c++98 -triple x86_64-linux-gnu -fenable-matrix -fclang-abi-compat=latest %s -emit-llvm -o - -Wno-c++11-extensions \
-// RUN:     | FileCheck --check-prefixes=CHECK,V39,V5,V12 %s
+// RUN:     | FileCheck --check-prefixes=CHECK,V39,V5,V12,V15 %s
 // RUN: %clang_cc1 -no-opaque-pointers -std=c++20 -triple x86_64-linux-gnu -fenable-matrix -fclang-abi-compat=latest %s -emit-llvm -o - \
-// RUN:     | FileCheck --check-prefixes=CHECK,V39,V5,V12,V12-CXX17,V12-CXX20,V13-CXX20 %s
+// RUN:     | FileCheck --check-prefixes=CHECK,V39,V5,V12,V12-CXX17,V12-CXX20,V13-CXX20,V15 %s
 
 typedef __attribute__((vector_size(8))) long long v1xi64;
 void clang39(v1xi64) {}
@@ -147,3 +149,14 @@ int observe_lambdas(T, U, V, W) { return 0; }
 inline auto inline_var_lambda = observe_lambdas([]{}, []{}, (int*)0, (int*)0);
 int use_inline_var_lambda() { return inline_var_lambda; }
 #endif
+
+struct X {
+  struct Y {
+    using a = int;
+    using b = int;
+  };
+};
+template <typename T> void test10(typename T::Y::a, typename T::Y::b, float*, float*) {}
+// PRE15: @_Z6test10I1XEvNT_1Y1aENS1_1Y1bEPfS4_
+// V15:   @_Z6test10I1XEvNT_1Y1aENS2_1bEPfS5_
+template void test10<X>(int, int, float*, float*);

clang/test/CodeGenCXX/mangle.cpp

@@ -1155,3 +1155,15 @@ namespace test60 {
   // CHECK-LABEL: @_ZN6test601fIiEEvDTplL_ZNS_1aEEcvT__EE
   template void f<int>(int);
 }
+
+namespace test61 {
+  struct X {
+    struct Y {
+      using a = int;
+      using b = int;
+    };
+  };
+  template <typename T> void f(typename T::Y::a, typename T::Y::b) {}
+  // CHECK-LABEL: @_ZN6test611fINS_1XEEEvNT_1Y1aENS3_1bE
+  template void f<X>(int, int);
+}