[clang] nonblocking/nonallocating attributes (was: nolock/noalloc) (PR #84983)

[Aaron Ballman via cfe-commits]

================
@@ -1870,6 +1870,28 @@ bool Sema::IsFunctionConversion(QualType FromType, QualType ToType,
       FromFn = QT->getAs<FunctionType>();
       Changed = true;
     }
+
+    // For C, when called from checkPointerTypesForAssignment,
+    // we need not to alter FromFn, or else even an innocuous cast
+    // like dropping effects will fail. In C++ however we do want to
+    // alter FromFn. TODO: Is this correct?
----------------
AaronBallman wrote:

I think I'm a bit surprised that `IsFunctionConversion()` would need this logic as opposed to `MergeFunctionDecl()` handling it.  Testing whether something is a function conversion doesn't seem like a time when we know we need to add or drop effects, it's only after we've decided to do something about the function conversion that would need that, right?

https://github.com/llvm/llvm-project/pull/84983