[15] RFR(S): 8239009: C2: Don't use PSHUF to load scalars from memory on x86

[Vladimir Ivanov]

Thanks for the reviews, Vladimir & Dean.

Best regards,
Vladimir Ivanov

On 05.03.2020 03:48, Vladimir Kozlov wrote:
> On 2/14/20 7:28 AM, Vladimir Ivanov wrote:
>>
>>> How many bytes are we loading from memory after your change?
>>
>> 4 bytes for int & float and 8 bytes for double.
>>
>> Wide memory accesses have both performance and correctness implications:
>>    * the access is not properly aligned (2-/4-/8-byte vs 16-byte)
>>    * can trigger page faults
>>
>> I noticed that the change in ReplS_mem is not enough: movdl loads 4 
>> bytes and there's no m16-to-xmmreg instruction available. So, I 
>> aligned ReplS_mem with ReplB_mem: use VPBROADCASTW when available 
>> (AVX2). Otherwise, it is matched as loadS + ReplS_reg.
> 
> Make sense.
> 
>>
>> Updated webrev:
>>    http://cr.openjdk.java.net/~vlivanov/8239009/webrev.01
> 
> Agree.
> 
> Thanks,
> Vladimir K
> 
>>
>> Best regards,
>> Vladimir Ivanov
>>
>>> On 2/13/20 8:04 AM, Vladimir Ivanov wrote:
>>>> http://cr.openjdk.java.net/~vlivanov/8239009/webrev.00
>>>> https://bugs.openjdk.java.net/browse/JDK-8239009
>>>>
>>>> Mem-to-reg variants of PSHUF instructions load 16 bytes from memory.
>>>>
>>>> Switch to reg-to-reg variants and perform scalar loads of proper 
>>>> size instead.
>>>>
>>>> Testing: hs-precheckin-comp,hs-tier1,hs-tier2
>>>>
>>>> Thanks!
>>>>
>>>> Best regards,
>>>> Vladimir Ivanov
>>>