[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]]
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vogelsgesang wrote:

Can we somehow turn this into a positive test? Negative tests can easily regress, e.g. if something else in the line would change.

Can we use a `$` (or some other mechanism) to check for the end of the line, and there by explicitly check that a call to `_Z10returnSamei(ptr {{.*}}, i32 noundef 3)` does exist, but does not have the ELIDE_SAFE annotation?

```suggestion
  // CHECK: call void @_Z10returnSamei(ptr {{.*}}, i32 noundef 3)$
```

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