[clang] [Clang] Propagate elide safe context through [[clang::coro_must_await]] (PR #108474)

[Adrian Vogelsgesang via cfe-commits]

================
@@ -84,4 +84,35 @@ Task<int> nonelidable() {
   co_return 1;
 }
 
+// CHECK-LABEL: define{{.*}} @_Z8addTasksO4TaskIiES1_{{.*}} {
+Task<int> addTasks([[clang::coro_must_await]] Task<int> &&t1, Task<int> &&t2) {
+  int i1 = co_await t1;
+  int i2 = co_await t2;
+  co_return i1 + i2;
+}
+
+// CHECK-LABEL: define{{.*}} @_Z10returnSamei{{.*}} {
+Task<int> returnSame(int i) {
+  co_return i;
+}
+
+// CHECK-LABEL: define{{.*}} @_Z21elidableWithMustAwaitv{{.*}} {
+Task<int> elidableWithMustAwait() {
+  // CHECK: call void @_Z10returnSamei(ptr {{.*}}, i32 noundef 2) 
#[[ELIDE_SAFE]]
+  // CHECK-NOT: call void @_Z10returnSamei(ptr {{.*}}, i32 noundef 3) 
#[[ELIDE_SAFE]]
+  co_return co_await addTasks(returnSame(2), returnSame(3));
+}
+
+template <typename... Args>
+Task<int> sumAll([[clang::coro_must_await]] Args && ... tasks);
+
+// CHECK-LABEL: define{{.*}} @_Z16elidableWithPackv{{.*}} {
+Task<int> elidableWithPack() {
----------------
vogelsgesang wrote:

maybe also add a test case for recursive elision? I.e. for something like

```
co_await sumAll(addTasks(returnSame(1), returnSame(2)), returnSame(3));
```

https://github.com/llvm/llvm-project/pull/108474
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