[clang] nonblocking/nonallocating attributes: 2nd pass caller/callee analysis (PR #99656)

[Doug Wyatt via cfe-commits]

================
@@ -0,0 +1,256 @@
+// RUN: %clang_cc1 -fsyntax-only -fblocks -fcxx-exceptions -std=c++20 -verify %s
+// These are in a separate file because errors (e.g. incompatible attributes) currently prevent
+// the FXAnalysis pass from running at all.
+
+// This diagnostic is re-enabled and exercised in isolation later in this file.
+#pragma clang diagnostic ignored "-Wperf-constraint-implies-noexcept"
+
+// --- CONSTRAINTS ---
+
+void nb1() [[clang::nonblocking]]
+{
+	int *pInt = new int; // expected-warning {{'nonblocking' function must not allocate or deallocate memory}}
+	delete pInt; // expected-warning {{'nonblocking' function must not allocate or deallocate memory}}
+}
+
+void nb2() [[clang::nonblocking]]
+{
+	static int global; // expected-warning {{'nonblocking' function must not have static locals}}
+}
+
+void nb3() [[clang::nonblocking]]
+{
+	try {
+		throw 42; // expected-warning {{'nonblocking' function must not throw or catch exceptions}}
+	}
+	catch (...) { // expected-warning {{'nonblocking' function must not throw or catch exceptions}}
+	}
+}
+
----------------
dougsonos wrote:

Tracking whether the violation originated from a member initializer, and changing "function" to "member initializer" in the diagnostic is a bunch of busywork but straightforward:

```
warning: 'nonblocking' member initializer must not allocate or deallocate memory [-Wfunction-effects]
   12 |         int *x = new int(42);

note: member initializer cannot be inferred 'nonblocking' because it allocates or deallocates memory
   28 |         int *x = new int(42);
```

In both cases this could be followed by a note "invoked by constructor here"...

https://github.com/llvm/llvm-project/pull/99656