As of clang 3.3, at least, you get warnings in both cases without even trying:
/* main.c */
short x = 2000000000;
int y = 1000000000 * 1000000000;
int main()
{
return 0;
}
Compile:
$ clang -c main.c
main.c:1:11: warning: implicit conversion from 'int' to 'short' changes value
from 2000000000 to -27648 [-Wconstant-conversion]
short x = 2000000000;
~ ^~~~~~~~~~
main.c:2:20: warning: overflow in expression; result is -1486618624 with type
'int' [-Winteger-overflow]
int y = 1000000000 * 1000000000;
^
2 warnings generated.