strength reduce or eliminate range checks for power-of-two sized arrays

Integer expressions which perform bitwise and can be proven to be less than or equal to either operand, as long as the compared operand is non-negative. In other words:
  (x & m) <= m, if and only if (m >= 0)

This means the left-hand test can be replaced by the simpler right-hand test.

There are also off-by-one versions, such as:
  (x & (m-1)) < m, if and only if (m > 0)

There are also unsigned versions:
  (x & m) u<= m, always
  (x & (m-1)) u< m, if and only if (m > 0)

The optimizer should recognize these patterns. They are common in implicitly generated range checks for power-of-two sized arrays:

  int hash = ...;
  int bucket = hash & (array.length-1);
  Entry e = array[bucket];

The range check is:
  (hash & (array.length-1)) u< array.length

This check can be strength reduced to:
  array.length != 0

If the array is constant, or if user code has a dominating check for an empty array, this check will go away completely.