Re: [PATCH 1/3] RISC-V: Add auto-vectorization compile option for RVV

[Jeff Law <jeffreyalaw@gmail.com>]

On 4/20/23 05:08, Richard Biener wrote:
> On Wed, Apr 19, 2023 at 6:38 PM <juzhe.zhong@rivai.ai> wrote:
>>
>> From: Ju-Zhe Zhong <juzhe.zhong@rivai.ai>
>>
>> This patch is adding 2 compile option for RVV auto-vectorization.
>> 1. -param=riscv-autovec-preference=
>>     This option is to specify the auto-vectorization approach for RVV.
>>     Currently, we only support scalable and fixed-vlmax.
>>
>>      - scalable means VLA auto-vectorization. The vector-length to compiler is
>>        unknown and runtime invariant. Such approach can allow us compile the code
>>        run on any vector-length RVV CPU.
>>
>>      - fixed-vlmax means the compile known the RVV CPU vector-length, compile option
>>        in fixed-length VLS auto-vectorization. Meaning if we specify vector-length=512.
>>        The execution file can only run on vector-length = 512 RVV CPU.
>>
>>      - TODO: we may need to support min-length VLS auto-vectorization, means the execution
>>        file can run on larger length RVV CPU.
> 
> Just as a generic comment - if the option should be exposed to users
> rather than just used
> for testsuite or development purposes it should eventually become a
> -mautovec-preference=
> flag (no need to prefix with riscv).
I would expect that we don't want users twiddling the autovectorization 
style in the long term.  I do support having the param so that we can 
can do A/B experiments across the styles to identify gaps.

jeff