Intel i960 - Page 75

gcc960 Compiler Driver
2-57
2
There may be no warning about a variable that is
used only to compute a value that itself is never
used, because such computations can be deleted
by data flow analysis before the warnings are
printed.
These warnings are optional because gcc960
cannot foresee all the reasons why the code
might be correct despite appearing to have an
error. Here is one example of how this can
happen:
{
int x;
switch (y)
{
case 1: x = 1;
break;
case 2: x = 4;
break;
case 3: x = 5;
}
foo (x);
}
When the value of y is always 1, 2 or 3, then x is
always initialized, but gcc960 doesn’t know this.
Here is another common case:
{
int save_y;
if (change_y) save_y = y, y = new_y;
...
if (change_y) y = save_y;
}