Re: [PATCH v4 02/12] tcg/riscv: Add basic support for vector

[Richard Henderson <richard.henderson@linaro.org>]

On 9/18/24 07:17, LIU Zhiwei wrote:
> 
> On 2024/9/12 2:41, Richard Henderson wrote:
>> On 9/11/24 06:26, LIU Zhiwei wrote:
>>> From: Swung0x48<swung0x48@outlook.com>
>>>
>>> The RISC-V vector instruction set utilizes the LMUL field to group
>>> multiple registers, enabling variable-length vector registers. This
>>> implementation uses only the first register number of each group while
>>> reserving the other register numbers within the group.
>>>
>>> In TCG, each VEC_IR can have 3 types (TCG_TYPE_V64/128/256), and the
>>> host runtime needs to adjust LMUL based on the type to use different
>>> register groups.
>>>
>>> This presents challenges for TCG's register allocation. Currently, we
>>> avoid modifying the register allocation part of TCG and only expose the
>>> minimum number of vector registers.
>>>
>>> For example, when the host vlen is 64 bits and type is TCG_TYPE_V256, with
>>> LMUL equal to 4, we use 4 vector registers as one register group. We can
>>> use a maximum of 8 register groups, but the V0 register number is reserved
>>> as a mask register, so we can effectively use at most 7 register groups.
>>> Moreover, when type is smaller than TCG_TYPE_V256, only 7 registers are
>>> forced to be used. This is because TCG cannot yet dynamically constrain
>>> registers with type; likewise, when the host vlen is 128 bits and
>>> TCG_TYPE_V256, we can use at most 15 registers.
>>>
>>> There is not much pressure on vector register allocation in TCG now, so
>>> using 7 registers is feasible and will not have a major impact on code
>>> generation.
>>>
>>> This patch:
>>> 1. Reserves vector register 0 for use as a mask register.
>>> 2. When using register groups, reserves the additional registers within
>>>     each group.
>>>
>>> Signed-off-by: TANG Tiancheng<tangtiancheng.ttc@alibaba-inc.com>
>>> Co-authored-by: TANG Tiancheng<tangtiancheng.ttc@alibaba-inc.com>
>>
>> If there is a co-author, there should be another Signed-off-by.
> 
> This patch has added a tag:
> 
> Signed-off-by: TANG Tiancheng<tangtiancheng.ttc@alibaba-inc.com>
> 
> 
> Do you mean we should add the same tag twice?

The from line is "Swung0x48 <swung0x48@outlook.com>".
If this is an alternate email for TANG Tiancheng, then please fix the patch --author.


r~