PR47792: 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. We're still missing the type from the mangling, so we continue
to be able to see collisions at link time; that's an open ABI issue.

clang/lib/AST/ASTContext.cpp

@@ -5890,7 +5890,7 @@ 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

@@ -244,7 +244,8 @@ void TemplateArgument::Profile(llvm::FoldingSetNodeID &ID,
     break;
 
   case Declaration:
-    ID.AddPointer(getAsDecl()? getAsDecl()->getCanonicalDecl() : nullptr);
+    ID.AddPointer(getAsDecl() ? getAsDecl()->getCanonicalDecl() : nullptr);
+    getParamTypeForDecl().Profile(ID);
     break;
 
   case Template:
@@ -294,7 +295,8 @@ bool TemplateArgument::structurallyEquals(const TemplateArgument &Other) const {
     return TypeOrValue.V == Other.TypeOrValue.V;
 
   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

@@ -459,3 +459,23 @@ namespace PR46637 {
   X<f> y;
   int n = y.call(); // expected-error {{cannot initialize a variable of type 'int' with an rvalue of type 'void *'}}
 }
+
+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'");
+
+  // FIXME: We will need to mangle these cases differently too!
+  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");
+}