(original) (raw)

It's totally reasonable, and is already filed as an RFE (please comment on it!):

  https://bugs.openjdk.java.net/browse/JDK-8003585

� John

On Feb 12, 2014, at 9:40 AM, Martin Grajcar <maaartinus@gmail.com> wrote:

Most hash tables are power-of-two sized so that they can use masking for the access. It looks like the bounds check doesn't get eliminated, although it could be.

Based on the equivalence a\[x & (a.length - 1)\] throws if and only if a.length == 0, I'm proposing this simple algorithm:

  • For each array access, check if the index has been computed via a bitwise and.
  • If so, check if either of the operands was computed as length minus one.
  • If so, replace the bounds check by a zero-length check.
This zero-length check can then be easily moved out of the loop by the existing optimizations.

I hope I'm not talking non-sense. For more details see 

Regards,
Martin.