[clang] [PAC] Add support for __ptrauth type qualifier (PR #100830)

[Oliver Hunt via cfe-commits]

================
@@ -0,0 +1,21 @@
+// RUN: %clang_cc1 -triple arm64-apple-ios -fsyntax-only -verify -fptrauth-intrinsics -std=c++11 %s
+// RUN: %clang_cc1 -triple aarch64-linux-gnu -fsyntax-only -verify -fptrauth-intrinsics -std=c++11 %s
+
+template <typename T> struct G {
+  T __ptrauth(0,0,1234) test;
+  // expected-error at -1 2 {{type '__ptrauth(0,0,1234) T' is already __ptrauth-qualified}}
+};
+
+template <typename T> struct Indirect {
+  G<T> layers;
+  // expected-note at -1{{in instantiation of template class 'G<void *__ptrauth(0,0,1235)>' requested here}}
+  // expected-note at -2{{in instantiation of template class 'G<void *__ptrauth(0,0,1234)>' requested here}}
+};
+
+void f3() {
+  Indirect<void* __ptrauth(0,0,1234)> one;
+  // expected-note at -1{{in instantiation of template class 'Indirect<void *__ptrauth(0,0,1234)>' requested here}}
+  Indirect<void* __ptrauth(0,0,1235)> two;
+  // expected-note at -1{{in instantiation of template class 'Indirect<void *__ptrauth(0,0,1235)>' requested here}}
+  Indirect<void*> three;
+}
----------------
ojhunt wrote:

@AaronBallman 

__ptrauth qualified pointers can be template parameters, and can be deduced, however the qualifier itself cannot be dependent, e.g.

```cpp
template <class T> struct Foo {
  T v;
  T *__ptrauth(1,1,1000) ptr;
};

```

Is valid, and can be instantiated as you would expect with `Foo<int>`, `Foo<int *>`, or `Foo<int *__ptrauth(1,1,1)>`.

However you can't use template parameters in the qualifier itself, e.g.

```cpp
template <unsigned u> struct Foo {
   void * __ptrauth(1,1,u) ptr;
}
```

is not valid, but that's just because supporting such has never been high enough on the priority list.

Because functions can't take __ptrauth qualified parameters something like

```
template <class T> void f(T);
...
void *__ptrauth (1,1,1) ptr;
f(ptr)
```

results in the type decaying during deduction so the deduced parameter type is just `void*`.


https://github.com/llvm/llvm-project/pull/100830