Consider reference, pointer, and pointer-to-member TemplateArguments …

…to be different if they have different types.

For the Itanium ABI, this implements the mangling rule suggested in
itanium-cxx-abi/cxx-abi#47, namely mangling
such template arguments as being cast to the parameter type in the case
where the template name is overloadable. This can cause a mangling
change for rare cases, where

 * the template argument declaration is converted from its declared type
   to the type of the template parameter, and
 * the template parameter either has a deduced type or is a parameter of
   a function template.

However, such changes are necessary to avoid mangling collisions. The
ABI changes can be reversed with -fclang-abi-compat=11 or earlier.

Re-commit with a fix for a couple of regressions.

Differential Revision: https://reviews.llvm.org/D91488

clang/include/clang/Basic/LangOptions.h

@@ -158,8 +158,10 @@ class LangOptions : public LangOptionsBase {
 
     /// Attempt to be ABI-compatible with code generated by Clang 11.0.x
     /// (git  2e10b7a39b93). This causes clang to pass unions with a 256-bit
-    /// vector member on the stack instead of using registers, and to not
-    /// properly mangle substitutions for template names in some cases.
+    /// vector member on the stack instead of using registers, to not properly
+    /// mangle substitutions for template names in some cases, and to mangle
+    /// declaration template arguments without a cast to the parameter type
+    /// even when that can lead to mangling collisions.
     Ver11,
 
     /// Conform to the underlying platform's C and C++ ABIs as closely

clang/lib/AST/StmtProfile.cpp

@@ -2193,6 +2193,8 @@ void StmtProfiler::VisitTemplateArgument(const TemplateArgument &Arg) {
     break;
 
   case TemplateArgument::Declaration:
+    VisitType(Arg.getParamTypeForDecl());
+    // FIXME: Do we need to recursively decompose template parameter objects?
     VisitDecl(Arg.getAsDecl());
     break;
 
@@ -2201,8 +2203,8 @@ void StmtProfiler::VisitTemplateArgument(const TemplateArgument &Arg) {
     break;
 
   case TemplateArgument::Integral:
-    Arg.getAsIntegral().Profile(ID);
     VisitType(Arg.getIntegralType());
+    Arg.getAsIntegral().Profile(ID);
     break;
 
   case TemplateArgument::Expression:

clang/lib/AST/TemplateBase.cpp

@@ -244,6 +244,7 @@ void TemplateArgument::Profile(llvm::FoldingSetNodeID &ID,
     break;
 
   case Declaration:
+    getParamTypeForDecl().Profile(ID);
     ID.AddPointer(getAsDecl()? getAsDecl()->getCanonicalDecl() : nullptr);
     break;
 

clang/lib/Sema/SemaTemplate.cpp

@@ -6631,8 +6631,8 @@ CheckTemplateArgumentAddressOfObjectOrFunction(Sema &S,
     return true;
 
   // Create the template argument.
-  Converted =
-      TemplateArgument(cast<ValueDecl>(Entity->getCanonicalDecl()), ParamType);
+  Converted = TemplateArgument(cast<ValueDecl>(Entity->getCanonicalDecl()),
+                               S.Context.getCanonicalType(ParamType));
   S.MarkAnyDeclReferenced(Arg->getBeginLoc(), Entity, false);
   return false;
 }
@@ -6753,7 +6753,7 @@ static bool CheckTemplateArgumentPointerToMember(Sema &S,
       Converted = TemplateArgument(Arg);
     } else {
       ValueDecl *D = cast<ValueDecl>(DRE->getDecl()->getCanonicalDecl());
-      Converted = TemplateArgument(D, ParamType);
+      Converted = TemplateArgument(D, S.Context.getCanonicalType(ParamType));
     }
     return Invalid;
   }

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

@@ -1,10 +1,12 @@
-// RUN: %clang_cc1 -std=c++17 -triple x86_64-linux-gnu -fclang-abi-compat=3.0 %s -emit-llvm -o - | FileCheck --check-prefixes=PRE39,PRE5,PRE12 %s
-// RUN: %clang_cc1 -std=c++17 -triple x86_64-linux-gnu -fclang-abi-compat=3.8 %s -emit-llvm -o - | FileCheck --check-prefixes=PRE39,PRE5,PRE12 %s
-// RUN: %clang_cc1 -std=c++17 -triple x86_64-linux-gnu -fclang-abi-compat=3.9 %s -emit-llvm -o - | FileCheck --check-prefixes=V39,PRE5,PRE12 %s
-// RUN: %clang_cc1 -std=c++17 -triple x86_64-linux-gnu -fclang-abi-compat=4.0 %s -emit-llvm -o - | FileCheck --check-prefixes=V39,PRE5,PRE12 %s
-// RUN: %clang_cc1 -std=c++17 -triple x86_64-linux-gnu -fclang-abi-compat=5 %s -emit-llvm -o - | FileCheck --check-prefixes=V39,V5,PRE12 %s
-// RUN: %clang_cc1 -std=c++17 -triple x86_64-linux-gnu -fclang-abi-compat=11 %s -emit-llvm -o - | FileCheck --check-prefixes=V11,V5,PRE12 %s
-// RUN: %clang_cc1 -std=c++17 -triple x86_64-linux-gnu -fclang-abi-compat=latest %s -emit-llvm -o - | FileCheck --check-prefixes=V39,V5,V12 %s
+// RUN: %clang_cc1 -std=c++98 -triple x86_64-linux-gnu -fclang-abi-compat=3.0 %s -emit-llvm -o -    | FileCheck --check-prefixes=CHECK,PRE39,PRE5,PRE12 %s
+// RUN: %clang_cc1 -std=c++17 -triple x86_64-linux-gnu -fclang-abi-compat=3.0 %s -emit-llvm -o -    | FileCheck --check-prefixes=CHECK,PRE39,PRE5,PRE12 %s
+// RUN: %clang_cc1 -std=c++17 -triple x86_64-linux-gnu -fclang-abi-compat=3.8 %s -emit-llvm -o -    | FileCheck --check-prefixes=CHECK,PRE39,PRE5,PRE12 %s
+// RUN: %clang_cc1 -std=c++17 -triple x86_64-linux-gnu -fclang-abi-compat=3.9 %s -emit-llvm -o -    | FileCheck --check-prefixes=CHECK,V39,PRE5,PRE12 %s
+// RUN: %clang_cc1 -std=c++17 -triple x86_64-linux-gnu -fclang-abi-compat=4.0 %s -emit-llvm -o -    | FileCheck --check-prefixes=CHECK,V39,PRE5,PRE12 %s
+// RUN: %clang_cc1 -std=c++17 -triple x86_64-linux-gnu -fclang-abi-compat=5 %s -emit-llvm -o -      | FileCheck --check-prefixes=CHECK,V39,V5,PRE12,PRE12-CXX17 %s
+// RUN: %clang_cc1 -std=c++17 -triple x86_64-linux-gnu -fclang-abi-compat=11 %s -emit-llvm -o -     | FileCheck --check-prefixes=CHECK,V39,V5,PRE12,PRE12-CXX17 %s
+// RUN: %clang_cc1 -std=c++98 -triple x86_64-linux-gnu -fclang-abi-compat=latest %s -emit-llvm -o - | FileCheck --check-prefixes=CHECK,V39,V5,V12 %s
+// RUN: %clang_cc1 -std=c++20 -triple x86_64-linux-gnu -fclang-abi-compat=latest %s -emit-llvm -o - | FileCheck --check-prefixes=CHECK,V39,V5,V12,V12-CXX17 %s
 
 typedef __attribute__((vector_size(8))) long long v1xi64;
 void clang39(v1xi64) {}
@@ -27,3 +29,29 @@ namespace mangle_template_prefix {
   void g() { f<T>(1, 2); }
 }
 
+int arg;
+template<const int *> struct clang12_unchanged {};
+// CHECK: @_Z4test17clang12_unchangedIXadL_Z3argEEE
+void test(clang12_unchanged<&arg>) {}
+
+#if __cplusplus >= 201703L
+// PRE12-CXX17: @_Z4test15clang12_changedIXadL_Z3argEEE
+// V12-CXX17: @_Z4test15clang12_changedIXcvPKiadL_Z3argEEE
+template<auto> struct clang12_changed {};
+void test(clang12_changed<(const int*)&arg>) {}
+#endif
+
+// PRE12: @_Z9clang12_aIXadL_Z3argEEEvv
+// V12: @_Z9clang12_aIXcvPKiadL_Z3argEEEvv
+template<const int *> void clang12_a() {}
+template void clang12_a<&arg>();
+
+// PRE12: @_Z9clang12_bIXadL_Z3arrEEEvv
+// V12: @_Z9clang12_bIXadsoKcL_Z3arrEEEEvv
+extern const char arr[6] = "hello";
+template<const char *> void clang12_b() {}
+template void clang12_b<arr>();
+
+// CHECK: @_Z9clang12_cIXadL_Z3arrEEEvv
+template<const char (*)[6]> void clang12_c() {}
+template void clang12_c<&arr>();

clang/test/CodeGenCXX/mangle-class-nttp.cpp

@@ -124,7 +124,7 @@ union E {
 template<E> void f() {}
 
 // Union members.
-// CHECK: define weak_odr void @_Z1fIXL1EEEEvv(
+// CHECK: define weak_odr void @_Z1fIL1EEEvv(
 // MSABI: define {{.*}} @"??$f@$7TE@@@@@YAXXZ"
 template void f<E{}>();
 // CHECK: define weak_odr void @_Z1fIXtl1EEEEvv(
@@ -214,10 +214,10 @@ template<H1> void f() {}
 template<H2> void f() {}
 template<H3> void f() {}
 template<H4> void f() {}
-// CHECK: define weak_odr void @_Z1fIXL2H1EEEvv
+// CHECK: define weak_odr void @_Z1fIL2H1EEvv
 // MSABI: define {{.*}} @"??$f@$7TH1@@@@@YAXXZ"
 template void f<H1{}>();
-// CHECK: define weak_odr void @_Z1fIXL2H2EEEvv
+// CHECK: define weak_odr void @_Z1fIL2H2EEvv
 // MSABI: define {{.*}} @"??$f@$7TH2@@@@@YAXXZ"
 template void f<H2{}>();
 // CHECK: define weak_odr void @_Z1fIXtl2H3EEEvv

clang/test/CodeGenCXX/mangle-template.cpp

@@ -1,4 +1,5 @@
 // RUN: %clang_cc1 -verify -Wno-return-type -Wno-main -std=c++11 -emit-llvm -triple %itanium_abi_triple -o - %s | FileCheck %s
+// RUN: %clang_cc1 -verify -Wno-return-type -Wno-main -std=c++20 -emit-llvm -triple x86_64-linux-gnu -o - %s | FileCheck %s --check-prefixes=CHECK,CXX20
 // expected-no-diagnostics
 
 namespace test1 {
@@ -221,3 +222,123 @@ namespace test16 {
   void g() { f<T>(1, 2); }
 }
 
+#if __cplusplus >= 202002L
+namespace cxx20 {
+  template<auto> struct A {};
+  template<typename T, T V> struct B {};
+
+  int x;
+  // CXX20: define {{.*}} @_ZN5cxx201fENS_1AIXadL_ZNS_1xEEEEE(
+  void f(A<&x>) {}
+  // CXX20: define {{.*}} @_ZN5cxx201fENS_1BIPiXadL_ZNS_1xEEEEE(
+  void f(B<int*, &x>) {}
+  // CXX20: define {{.*}} @_ZN5cxx201fENS_1AIXcvPKiadL_ZNS_1xEEEEE(
+  void f(A<(const int*)&x>) {}
+  // CXX20: define {{.*}} @_ZN5cxx201fENS_1BIPKiXadL_ZNS_1xEEEEE(
+  void f(B<const int*, &x>) {}
+  // CXX20: define {{.*}} @_ZN5cxx201fENS_1AIXcvPvadL_ZNS_1xEEEEE(
+  void f(A<(void*)&x>) {}
+  // CXX20: define {{.*}} @_ZN5cxx201fENS_1BIPvXadL_ZNS_1xEEEEE(
+  void f(B<void*, (void*)&x>) {}
+  // CXX20: define {{.*}} @_ZN5cxx201fENS_1AIXcvPKvadL_ZNS_1xEEEEE(
+  void f(A<(const void*)&x>) {}
+  // CXX20: define {{.*}} @_ZN5cxx201fENS_1BIPKvXadL_ZNS_1xEEEEE(
+  void f(B<const void*, (const void*)&x>) {}
+
+  struct Q { int x; };
+
+  // CXX20: define {{.*}} @_ZN5cxx201fENS_1AIXadL_ZNS_1Q1xEEEEE(
+  void f(A<&Q::x>) {}
+  // CXX20: define {{.*}} @_ZN5cxx201fENS_1BIMNS_1QEiXadL_ZNS1_1xEEEEE
+  void f(B<int Q::*, &Q::x>) {}
+  // CXX20: define {{.*}} @_ZN5cxx201fENS_1AIXcvMNS_1QEKiadL_ZNS1_1xEEEEE(
+  void f(A<(const int Q::*)&Q::x>) {}
+  // CXX20: define {{.*}} @_ZN5cxx201fENS_1BIMNS_1QEKiXadL_ZNS1_1xEEEEE(
+  void f(B<const int Q::*, (const int Q::*)&Q::x>) {}
+}
+#endif
+
+namespace test17 {
+  // Ensure we mangle the types for non-type template arguments if we've lost
+  // track of argument / parameter correspondence.
+  template<int A, int ...B> struct X {};
+
+  // CHECK: define {{.*}} @_ZN6test171fILi1EJLi2ELi3ELi4EEEEvNS_1XIXT_EJLi5EXspT0_ELi6EEEE
+  template<int D, int ...C> void f(X<D, 5u, C..., 6u>) {}
+  void g() { f<1, 2, 3, 4>({}); }
+
+  // Note: there is no J...E here, because we can't form a pack argument, and
+  // the 5u and 6u are mangled with the original type 'j' (unsigned int) not
+  // with the resolved type 'i' (signed int).
+  // CHECK: define {{.*}} @_ZN6test171hILi4EJLi1ELi2ELi3EEEEvNS_1XIXspT0_EXLj5EEXT_EXLj6EEEE
+  template<int D, int ...C> void h(X<C..., 5u, D, 6u>) {}
+  void i() { h<4, 1, 2, 3>({}); }
+
+#if __cplusplus >= 201402L
+  template<int A, const volatile int*> struct Y {};
+  int n;
+  // Case 1: &n is a resolved template argument, with a known parameter:
+  // mangled with no conversion.
+  // CXX20: define {{.*}} @_ZN6test172j1ILi1EEEvNS_1YIXT_EXadL_ZNS_1nEEEEE
+  template<int N> void j1(Y<N, (const int*)&n>) {}
+  // Case 2: &n is an unresolved template argument, with an unknown
+  // corresopnding parameter: mangled as the source expression.
+  // CXX20: define {{.*}} @_ZN6test172j2IJLi1EEEEvNS_1YIXspT_EXcvPKiadL_ZNS_1nEEEEE
+  template<int ...Ns> void j2(Y<Ns..., (const int*)&n>) {}
+  // Case 3: &n is a resolved template argument, with a known parameter, but
+  // for a template that can be overloaded on type: mangled with the parameter type.
+  // CXX20: define {{.*}} @_ZN6test172j3ILi1EEEvDTplT_clL_ZNS_1yIXcvPVKiadL_ZNS_1nEEEEEivEEE
+  template<const volatile int*> int y();
+  template<int N> void j3(decltype(N + y<(const int*)&n>())) {}
+  void k() {
+    j1<1>(Y<1, &n>());
+    j2<1>(Y<1, &n>());
+    j3<1>(0);
+  }
+#endif
+}
+
+namespace partially_dependent_template_args {
+  namespace test1 {
+    template<bool B> struct enable { using type = int; };
+    template<typename ...> struct and_ { static constexpr bool value = true; };
+    template<typename T> inline typename enable<and_<T, T, T>::value>::type f(T) {}
+    // FIXME: GCC and ICC form a J...E mangling for the pack here. Clang
+    // doesn't do so when mangling an <unresolved-prefix>. It's not clear who's
+    // right. See https://github.com/itanium-cxx-abi/cxx-abi/issues/113.
+    // CHECK: @_ZN33partially_dependent_template_args5test11fIiEENS0_6enableIXsr4and_IT_S3_S3_EE5valueEE4typeES3_
+    void g() { f(0); }
+  }
+
+  namespace test2 {
+    struct X { int n; };
+    template<unsigned> int f(X);
+
+    template<typename T> void g1(decltype(f<0>(T()))) {}
+    template<typename T> void g2(decltype(f<0>({}) + T())) {}
+    template<typename T> void g3(decltype(f<0>(X{}) + T())) {}
+    template<int N> void g4(decltype(f<0>(X{N})));
+
+    // The first of these mangles the unconverted argument Li0E because the
+    // callee is unresolved, the rest mangle the converted argument Lj0E
+    // because the callee is resolved.
+    void h() {
+      // CHECK: @_ZN33partially_dependent_template_args5test22g1INS0_1XEEEvDTcl1fIXLi0EEEcvT__EEE
+      g1<X>({});
+      // CHECK: @_ZN33partially_dependent_template_args5test22g2IiEEvDTplclL_ZNS0_1fILj0EEEiNS0_1XEEilEEcvT__EE
+      g2<int>({});
+      // CHECK: @_ZN33partially_dependent_template_args5test22g3IiEEvDTplclL_ZNS0_1fILj0EEEiNS0_1XEEtlS3_EEcvT__EE
+      g3<int>({});
+      // CHECK: @_ZN33partially_dependent_template_args5test22g4ILi0EEEvDTclL_ZNS0_1fILj0EEEiNS0_1XEEtlS3_T_EEE
+      g4<0>({});
+    }
+  }
+}
+
+namespace fixed_size_parameter_pack {
+  template<typename ...T> struct A {
+    template<T ...> struct B {};
+  };
+  template<int ...Ns> void f(A<unsigned, char, long long>::B<0, Ns...>);
+  void g() { f<1, 2>({}); }
+}

clang/test/SemaTemplate/temp_arg_nontype.cpp

@@ -514,3 +514,15 @@ namespace type_of_pack {
     }
   };
 }
+
+namespace match_type_after_substitution {
+  template<typename T> struct X {};
+  X<int> y;
+  template<typename T, X<T> &Y> struct B {
+    typedef B<T, Y> Self;
+  };
+
+  // These two formulations should resolve to the same type.
+  typedef B<int, y> Z;
+  typedef Z::Self Z;
+}

clang/test/SemaTemplate/temp_arg_nontype_cxx1z.cpp

@@ -187,6 +187,11 @@ namespace Auto {
     int &r = f(B<&a>());
     float &s = f(B<&b>());
 
+    void type_affects_identity(B<&a>) {}
+    void type_affects_identity(B<(const int*)&a>) {}
+    void type_affects_identity(B<(void*)&a>) {}
+    void type_affects_identity(B<(const void*)&a>) {}
+
     // pointers to members
     template<typename T, auto *T::*p> struct B<p> {};
     template<typename T, auto **T::*p> struct B<p> {};
@@ -198,6 +203,12 @@ namespace Auto {
     char &u = f(B<&X::p>());
     short &v = f(B<&X::pp>());
 
+    struct Y : X {};
+    void type_affects_identity(B<&X::n>) {}
+    void type_affects_identity(B<(int Y::*)&X::n>) {} // FIXME: expected-error {{sorry}}
+    void type_affects_identity(B<(const int X::*)&X::n>) {}
+    void type_affects_identity(B<(const int Y::*)&X::n>) {} // FIXME: expected-error {{sorry}}
+
     // A case where we need to do auto-deduction, and check whether the
     // resulting dependent types match during partial ordering. These
     // templates are not ordered due to the mismatching function parameter.