RFR: 8073093: AARCH64: C2 generates poor code for ByteBuffer accesses

[Andrew Haley]

On 02/17/2015 10:49 AM, Florian Weimer wrote:
> On 02/17/2015 11:22 AM, Andrew Haley wrote:
>>> You'll still have to allocate a wrapping ByteBuffer object to use them.
>>>  I expect that makes them unattractive in many cases.
>>
>> Hmm.  I'm having a hard time trying to understand why.  If you need to
>> do a lot of accesses the allocation of the ByteBuffer won't be
>> significant; if you don't need to do a lot of accesses it won't
>> matter either.
> 
> The typical use case I have in mind is exemplified by
> com.sun.crypto.provider.GHASH(processBlock(byte[] data, int ofs):
> 
>  174     private void processBlock(byte[] data, int ofs) {
>  175         if (data.length - ofs < AES_BLOCK_SIZE) {
>  176             throw new RuntimeException("need complete block");
>  177         }
>  178         state0 ^= getLong(data, ofs);
>  179         state1 ^= getLong(data, ofs + 8);
>  180         blockMult(subkeyH0, subkeyH1);
>  181     }
> 
> That is, the byte array is supplied by the caller, and if we wanted to
> use a ByteBuffer, we would have to allocate a fresh one on every
> iteration.  In this case, neither of the two alternatives you list apply.

I see.  So the question could also be whether escape analysis would
notice that a ByteBuffer does not escape.  I hope to know that soon.

Andrew.