[aarch64-port-dev ] RFR: JDK-8185786: AArch64: disable some address reshapings.

[Zhongwei Yao]

Hi, all,

Thanks for your review and information!

Patch is updated: http://cr.openjdk.java.net/~njian/8185786/webrev.01/

On 5 August 2017 at 01:53, Pinski, Andrew <Andrew.Pinski at cavium.com> wrote:
> FYI. Some future ones cause the shift to be splitted off while others will
> not split it and still be free.
>
>
>
> Sent via the Samsung Galaxy S7 edge, an AT&T 4G LTE smartphone
>
>
> -------- Original message --------
> From: "White, Derek" <Derek.White at cavium.com>
> Date: 8/4/17 8:33 AM (GMT-08:00)
> To: Andrew Haley <aph at redhat.com>, Zhongwei Yao <zhongwei.yao at linaro.org>,
> aarch64-port-dev at openjdk.java.net
> Subject: Re: [aarch64-port-dev ] RFR: JDK-8185786: AArch64: disable some
> address reshapings.
>
> FYI,
>
> The Cavium T88 CPU doesn't have this scaling penalty, but future CPUs may.
>
>  - Derek
>
>> -----Original Message-----
>> From: aarch64-port-dev [mailto:aarch64-port-dev-
>> bounces at openjdk.java.net] On Behalf Of Andrew Haley
>> Sent: Friday, August 04, 2017 9:33 AM
>> To: Zhongwei Yao <zhongwei.yao at linaro.org>; aarch64-port-
>> dev at openjdk.java.net
>> Subject: Re: [aarch64-port-dev ] RFR: JDK-8185786: AArch64: disable some
>> address reshapings.
>>
>> On 04/08/17 10:48, Zhongwei Yao wrote:
>> > Hi, all,
>> >
>> > Bug:
>> > https://bugs.openjdk.java.net/browse/JDK-8185786/
>> >
>> > Webrev:
>> > http://cr.openjdk.java.net/~njian/8185786/webrev.00/
>> >
>> > According to [1-2], ldrh/ldrsh scale by 2 is a bit slower than the
>> > non-scale version on modern Cortex-A cores.
>>
>> Yes, I see.  But from what I remember, without this reshape_address()
>> change there was some nasty code generated elsewhere.  Still, I suppose
>> it's
>> only for short.
>>
>> Is it possible to take this logic and push it into a suitable class,
>> VM_Version,
>> perhaps?  GCC uses a table, indexed by the mode of the operand.  We could
>> have
>>
>> +        if (!u->is_Mem() || u->is_LoadVector() || u->is_StoreVector() ||
>> u-
>> >Opcode() == Op_StoreCM ||
>> +            (VM_Version::expensive_access(u->Opcode()->type()),
>> + Op_LShiftL)) {
>>
>> ... or something.
>>
>> --
>> Andrew Haley
>> Java Platform Lead Engineer
>> Red Hat UK Ltd. <https://www.redhat.com>
>> EAC8 43EB D3EF DB98 CC77 2FAD A5CD 6035 332F A671



-- 
Best regards,
Zhongwei