[clang][bytecode] Fix a crash in overflow builtins

Only initialize pointers that can be initialized.

Author: tbaederr

clang/lib/AST/ByteCode/InterpBuiltin.cpp

@@ -861,7 +861,9 @@ static bool interp__builtin_overflowop(InterpState &S, CodePtr OpPC,
 
   // Write Result to ResultPtr and put Overflow on the stack.
   assignInteger(S, ResultPtr, ResultT, Result);
-  ResultPtr.initialize();
+  if (ResultPtr.canBeInitialized())
+    ResultPtr.initialize();
+
   assert(Call->getDirectCallee()->getReturnType()->isBooleanType());
   S.Stk.push<Boolean>(Overflow);
   return true;

clang/test/AST/ByteCode/builtin-functions.cpp

@@ -1753,4 +1753,12 @@ namespace I128Mul {
 }
 #endif
 
+namespace InitParam {
+  constexpr int foo(int a) {
+      __builtin_mul_overflow(20, 10, &a);
+      return a;
+  }
+  static_assert(foo(10) == 200);
+}
+
 #endif