[clang] [Wunsafe-buffer-usage] Turn off unsafe-buffer warning for methods annotated with clang::unsafe_buffer_usage attribute (PR #125671)

[Malavika Samak via cfe-commits]

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@@ -245,3 +243,40 @@ struct AggregateViaDefaultInit {
 void testAggregateViaDefaultInit() {
     AggregateViaDefaultInit A;
 };
+
+struct A {
+  int arr[2];
+
+  [[clang::unsafe_buffer_usage]]
+  int *ptr;
+};
+
+namespace std{
+  template <typename T> class span {
+
+   T *elements;
+
+   public:
+
+   constexpr span(T *, unsigned){}
+
+   template<class Begin, class End>
+   constexpr span(Begin first, End last){}
+
+   constexpr T* data() const noexcept {
+     return elements;
+   }
+ };
+}
+
+[[clang::unsafe_buffer_usage]]
+void check_no_warnings(unsigned idx) {
+  int *arr = new int[20];
+
+  int k = arr[idx]; // no-warning
+
+  std::span<int> sp = {arr, 20}; // no-warning
+  A *ptr = reinterpret_cast<A*> (sp.data()); // no-warning
+  A a;
+  a.ptr = arr; // no-warning
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malavikasamak wrote:

@dtarditi  We do not yet support adding the clang::unsafe_buffer_usage attribute to templated functions yet. Can't recall if this was intentional. I can create another PR to add this if we think it is necessary. 

I have added tests for other cases you suggested. Please take a look.

https://github.com/llvm/llvm-project/pull/125671