Reduced performance in Java 9.0.1 (vs 8u152)

[Roland Westrelin]

> The decompressor uses Unsafe.copyMemory() for the tail of the data block,
> so it shouldn't be called so frequently that it would affect performance
> that much. Do you think the mere presence of those checks (and, thus, extra
> code in the optimization window) may have some effect on the JIT's ability
> to optimize the rest of the code?

The fast copy loop with getLong/putLong has an extra spill when the
checks are present. So they affect register allocation at least.

Roland.