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

Dean Long dean.long at oracle.com
Sat Feb 14 22:10:59 UTC 2015

On 2/14/2015 12:07 AM, Andrew Haley wrote:
> On 02/13/2015 10:52 PM, Dean Long wrote:
>> My understanding is that whether or not aarch64 allows unaligned
>> accesses is based on a system setting, so this change is too
>> simplistic.
> Disabling unaligned access would be a really perverse thing to do, and
> I suspect that GCC and glibc already assume that unaligned accesses
> work so it would require a recompilation of libjvm (and probably the
> whole OS) to make it work.  However, if you really think there's a
> point to making this a runtime flag I won't resist.
> Andrew.

Even if linux-aarch64 always allows unaligned, checking only for 
"aarch64" is not future-proof
because it doesn't take the OS into account.  However, I really don't 
like having to enumerate
all relevant platforms in multiple places in shared code, so I disagree 
with the existing code
and with perpetuating the pattern.  As long as the decision is in 
platform-specific code, a build-time
decision may be entirely appropriate.


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