[clang] Include the type of a pointer or reference non-type template …

…parameter in its notion of template argument identity.

We already did this for all the other kinds of non-type template
argument.

Note: Based on earlier reverted patch from zygoloid.

Differential Revision: https://reviews.llvm.org/D136803

clang/docs/ReleaseNotes.rst

@@ -255,6 +255,9 @@ Bug Fixes
 - Reject non-type template arguments formed by casting a non-zero integer
   to a pointer in pre-C++17 modes, instead of treating them as null
   pointers.
+- Fix template arguments of pointer and reference not taking the type as
+  part of their identity.
+  `Issue 47136 <https://github.com/llvm/llvm-project/issues/47136>`_
 
 Improvements to Clang's diagnostics
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

clang/lib/AST/ASTContext.cpp

@@ -6771,7 +6771,7 @@ ASTContext::getCanonicalTemplateArgument(const TemplateArgument &Arg) const {
 
     case TemplateArgument::Declaration: {
       auto *D = cast<ValueDecl>(Arg.getAsDecl()->getCanonicalDecl());
-      return TemplateArgument(D, Arg.getParamTypeForDecl());
+      return TemplateArgument(D, getCanonicalType(Arg.getParamTypeForDecl()));
     }
 
     case TemplateArgument::NullPtr:

clang/lib/AST/TemplateBase.cpp

@@ -363,7 +363,8 @@ bool TemplateArgument::structurallyEquals(const TemplateArgument &Other) const {
            TemplateArg.NumExpansions == Other.TemplateArg.NumExpansions;
 
   case Declaration:
-    return getAsDecl() == Other.getAsDecl();
+    return getAsDecl() == Other.getAsDecl() &&
+           getParamTypeForDecl() == Other.getParamTypeForDecl();
 
   case Integral:
     return getIntegralType() == Other.getIntegralType() &&

clang/test/SemaTemplate/temp_arg_nontype_cxx1z.cpp

@@ -579,3 +579,22 @@ class Derived : Base<Derived>{
   }
 };
 } // no_crash
+
+namespace PR47792 {
+  using I = int;
+
+  template<decltype(auto)> int a;
+  const int n = 0;
+  const I n2 = 0;
+  static_assert(&a<n> == &a<0>, "both should have type 'int'");
+  static_assert(&a<n2> == &a<0>, "both should have type 'int'");
+
+  int m;
+  const int &r1 = m;
+  int &r2 = m;
+  static_assert(&a<r1> != &a<r2>, "should have different types");
+
+  const I &r3 = m;
+  static_assert(&a<r1> == &a<r3>, "should have different types");
+  static_assert(&a<r2> != &a<r3>, "should have different types");
+}