Array bounds checks

Thu Oct 26 10:52:00 GMT 2000

Per> Some compilers generate code twice:
Per> [ ... ]
Per> I don't particularly care for this idea ...
Another approach is to modify the bounds:
 __upper = min (upper, array.length)
 for (int i = 0; i < __upper; i++)
 ... no bounds checking ...
 for (; i < upper; i++)
 ... bounds checking ...
This gives better performance. I guess you don't even need a second
loop, just a copy of the body with bounds checking enabled.
Per> But as for the questions why the compiler cannot optimize away
Per> the bounds check in your example, I don't know. I thought there
Per> was code in gcc to do some range analysis and bounds check
Per> removal.
My impression is that the value range code only handles constants, not
things like `array.length'. I recommend asking on the gcc list to get
the real answer though.
Tom