[clang][Interp] Avoid calling invalid functions

Check if the non-null function pointer is even valid before calling
the function.

Author: tbaederr

clang/lib/AST/Interp/FunctionPointer.h

@@ -32,6 +32,7 @@ class FunctionPointer final {
 
   const Function *getFunction() const { return Func; }
   bool isZero() const { return !Func; }
+  bool isValid() const { return Valid; }
   bool isWeak() const {
     if (!Func || !Valid)
       return false;

clang/lib/AST/Interp/Interp.h

@@ -2236,6 +2236,10 @@ inline bool CallPtr(InterpState &S, CodePtr OpPC, uint32_t ArgSize,
         << const_cast<Expr *>(E) << E->getSourceRange();
     return false;
   }
+
+  if (!FuncPtr.isValid())
+    return false;
+
   assert(F);
 
   // Check argument nullability state.

clang/test/AST/Interp/functions.cpp

@@ -584,9 +584,20 @@ namespace VariadicOperator {
 namespace WeakCompare {
   [[gnu::weak]]void weak_method();
   static_assert(weak_method != nullptr, ""); // both-error {{not an integral constant expression}} \
-                                         // both-note {{comparison against address of weak declaration '&weak_method' can only be performed at runtim}}
+                                             // both-note {{comparison against address of weak declaration '&weak_method' can only be performed at runtim}}
 
   constexpr auto A = &weak_method;
   static_assert(A != nullptr, ""); // both-error {{not an integral constant expression}} \
-                               // both-note {{comparison against address of weak declaration '&weak_method' can only be performed at runtim}}
+                                   // both-note {{comparison against address of weak declaration '&weak_method' can only be performed at runtim}}
+}
+
+namespace FromIntegral {
+#if __cplusplus >= 202002L
+  typedef double (*DoubleFn)();
+  int a[(int)DoubleFn((void*)-1)()]; // both-error {{not allowed at file scope}} \
+                                    // both-warning {{variable length arrays}}
+  int b[(int)DoubleFn((void*)(-1 + 1))()]; // both-error {{not allowed at file scope}} \
+                                           // expected-note {{evaluates to a null function pointer}} \
+                                           // both-warning {{variable length arrays}}
+#endif
 }