RFR: 8234331: Add robust and optimized utility for rounding up to next power of two+

[Ivan Gerasimov]

Hi Claes!

In the code in align.hpp it is assumed that (1U << 32) == 0, which is 
not guaranteed.

In fact, if the right argument of the shift operator is >= 32 (for 
32-bit left argument) then the behavior is undefined, and thus is 
compiler specific.

With kind regards,

Ivan


On 11/26/19 1:44 AM, Claes Redestad wrote:
> Hi,
>
> in various places in the hotspot we have custom code to calculate the
> next power of two, some of which have potential to go into an infinite 
> loop in case of an overflow.
>
> This patch proposes adding next_power_of_two utility methods which
> avoid infinite loops on overflow, while providing slightly more
> efficient code in most cases.
>
> Bug:    https://bugs.openjdk.java.net/browse/JDK-8234331
> Webrev: http://cr.openjdk.java.net/~redestad/8234331/open.01/
>
> Testing: tier1-3
>
> Thanks!
>
> /Claes

-- 
With kind regards,
Ivan Gerasimov