[clang] [Clang][SPIRV] Add __spirv_event_t builtin type (PR #207077)

[Tom Honermann via cfe-commits]

================
@@ -0,0 +1,26 @@
+// REQUIRES: spirv-registered-target
+// RUN: %clang_cc1 -fsyntax-only -verify -std=gnu++11 -triple spirv64 -Wno-unused-value %s
+
+// __spirv_event_t is an opaque type: it cannot be initialized from, converted
+// to, or cast from other types, nor used in arithmetic. It cannot be used in
+// constant evaluation.
+void foo() {
+  int n = 100;
+  __spirv_event_t v = 0; // expected-error {{cannot initialize a variable of type '__spirv_event_t' with an rvalue of type 'int'}}
+  static_cast<__spirv_event_t>(n); // expected-error {{static_cast from 'int' to '__spirv_event_t' is not allowed}}
+  reinterpret_cast<__spirv_event_t>(n); // expected-error {{reinterpret_cast from 'int' to '__spirv_event_t' is not allowed}}
+  (void)(v + v); // expected-error {{invalid operands to binary expression ('__spirv_event_t' and '__spirv_event_t')}}
+  int x(v); // expected-error {{cannot initialize a variable of type 'int' with an lvalue of type '__spirv_event_t'}}
+  __spirv_event_t k;
+  int *ip = (int *)k; // expected-error {{cannot cast from type '__spirv_event_t' to pointer type 'int *'}}
+  constexpr __spirv_event_t e; // expected-error {{constexpr variable cannot have non-literal type 'const __spirv_event_t'}}
+}
+
+template <__spirv_event_t V> void baz(); // expected-error {{a non-type template parameter cannot have type '__spirv_event_t'}}
+
+// __spirv_event_t can be used as a function parameter, a template argument, and
+// a struct field.
+template <class T> void bar(T);
+void use(__spirv_event_t r) { bar(r); }
+struct S { __spirv_event_t r; int a; };
----------------
tahonermann wrote:

`__spirv_event_t` objects should be copyable and moveable, correct? Tests for copy construction, move construction, copy assignment, and move assignment would all be useful.

SPIR-V event objects are reference counted. Does that imply that `OpRetainEvent` and `OpReleaseEvent` operations should occur on copy/move construction/assignment?

https://github.com/llvm/llvm-project/pull/207077