The test case for codegen-4634 has both a va_list declaration and a use of va_start. If the two are placed together, by moving the va_list declaration into the scope with the va_start, the problem does not occur. The general workaround is to ensure an expression appears before the first nested scope. Exactly how to do that will depend on the situation.

A function with a nested scope that declares local variables and appears before any expressions in the function, and also declares top-level locals after that, may mishandle the local variables in a way that acts as though some share a location though they're supposed to be distinct. I.e.,   int test(int arg, ...)   {     { int a = 0; }     int b; may mishandle a, b, arg, or any extra arguments. Known cases all involve the ellipsis (...) parameter, but it is not known if that is also a necessary prerequisite.