[PATCH v2 2/2] gas, aarch64: Add SVE2 lut extension

[Saurabh Jha]

On 5/20/2024 2:34 PM, Richard Earnshaw (lists) wrote:
> On 16/05/2024 11:37, Saurabh Jha wrote:
>> Introduces instructions for the SVE2 lut extension for AArch64. They are documented in the following links:
>> * luti2: https://developer.arm.com/documentation/ddi0602/2024-03/SVE-Instructions/LUTI2--Lookup-table-read-with-2-bit-indices-?lang=en
>> * luti4: https://developer.arm.com/documentation/ddi0602/2024-03/SVE-Instructions/LUTI4--Lookup-table-read-with-4-bit-indices-?lang=en
>>
>> These instructions use new SVE2 vector operands. They are called
>> SVE_Zm1_23_INDEX, SVE_Zm2_22_INDEX, and Zm3_12_INDEX and they have
>> 1 bit, 2 bit, and 3 bit indices respectively.
>>
>> For these new operands, we defined a new inserter and a new extractor.
>>
>> The lsb and width of these new operands are the same as many existing
>> operands but the convention is to give different names to fields that
>> serve different purpose so we introduced new fields in aarch64-opc.c
>> and aarch64-opc.h.
>>
>> We made a design choice for the second operand of the halfword variant of
>> luti4 with two register tables. We could have either defined a new operand,
>> like SVE_Znx2, or we could have use the existing operand SVE_ZnxN. With
>> the new operand, we would need to implement constraints on register
>> lists based on either operand or opcode flag. With existing operand, we
>> could just existing constraint checks using opcode flag. We chose
>> the second approach and went with SVE_ZnxN and added opcode flag to
>> enforce lengths of vector register list operands. This way, we can reuse
>> the existing constraint check logic.
>> ---
>> Hi,
>>
>> Regression tested for aarch64-none-elf and found no regressions.
>>
>> Ok for binutils-master? I don't have commit access so can someone please commit on my behalf?
>>
>> Regards,
>> Saurabh
> 
> Similar comments as for patch 1/2, but additionally:
> 
> +  28:	45e0b800 	luti2	z0.h, \{z0.h\}, z0\[7\]
> 
> The immediate field for the '[7]' index is split over two locations in the encoded pattern, so I think it's worth some additional checks here that the field is encoded in the right way.  I'd suggest adding '[1]' and '[4]' variants.
> 
> +  68:	4520b7c0 	luti4	z0.h, \{z30.h-z31.h\}, z0\[0\]
> 
> We should probably also check the wrap-around case of '{z31.h, z0.h}'
> 
> Otherwise this looks OK.
> 
> R.

Thanks for the review Richard.

I have addressed the comments here and also applied the suggestions from 
the previous email of the patch list to this patch. I have sent a new 
patch series and the email corresponding to this patch is here 
https://sourceware.org/pipermail/binutils/2024-May/134195.html