RFR(M): 8248188: [PATCH] Add HotSpotIntrinsicCandidate and API for Base64 decoding

[Corey Ashford]

Due to the switchover to Git from Mercurial, this patch set got a new 
thread on the mailing lists on 9/24, but it has the same title. as this 
thread.

- Corey

On 9/7/20 3:08 AM, Doerr, Martin wrote:
> Hi Corey,
> 
> thanks for investigating.
> 
> Note that we use xlclang++ on AIX. It may possibly understand the directives as gcc on linux.
> Gcc 7.3.1 is the minimum for BE linux.
> But if you protect your code by #ifdef VM_LITTLE_ENDIAN no compiler except gcc >= 7.4.0 should ever look at it.
> 
> Best regards,
> Martin
> 
> 
>> -----Original Message-----
>> From: Corey Ashford <cjashfor at linux.ibm.com>
>> Sent: Dienstag, 1. September 2020 02:17
>> To: Doerr, Martin <martin.doerr at sap.com>
>> Cc: Michihiro Horie <HORIE at jp.ibm.com>; hotspot-compiler-
>> dev at openjdk.java.net; core-libs-dev <core-libs-dev at openjdk.java.net>;
>> Kazunori Ogata <OGATAK at jp.ibm.com>; joserz at br.ibm.com
>> Subject: Re: RFR(M): 8248188: [PATCH] Add HotSpotIntrinsicCandidate and
>> API for Base64 decoding
>>
>> On 8/27/20 8:07 AM, Doerr, Martin wrote:
>>>>> I will use __attribute__ ((align(16))) instead of __vector, and make
>>>> them arrays of 16 unsigned char.
>>> Maybe __vectors works as expected, too, now. Whatever we use, I'd
>> appreciate to double-check the alignment e.g. by using gdb.
>>> I don't remember what we had tried and why it didn't work as desired.
>>
>>
>> I just now tried on gcc-7.5.0, declaring a __vector at 1, 2, 3, 8, 9,
>> and 15 byte offsets in a struct, trying to force a misalignment, but the
>> compiler realigned all of them on 16-byte boundaries.
>>
>> If someone decides to make the intrinsic work on AIX (big endian), and
>> compiles with 7.3.1, I don't know what will happen w.r.t. alignment, so
>> to be on the safe side, I will make the declarations 16-byte unsigned
>> char arrays with an align attribute.
>>
>> Looking a bit deeper, I see that the __vector type comes out of the C
>> preprocessor as: __attribute__((altivec(vector__))). It's part of the
>> compiler's basic set of predefined macros, and can be seen using this
>> command:
>>
>> %  gcc -dM -E - < /dev/null | grep __vector
>>
>> #define __vector __attribute__((altivec(vector__)))
>>
>> Some information here:
>> https://gcc.gnu.org/onlinedocs/gcc/PowerPC-Type-Attributes.html
>>
>> I don't know if this is helpful or not, but it might answer part of your
>> question about the meaning of __vector.
>>
>> Regards,
>>
>> - Corey