Re: [PATCH V7] RISC-V: RISC-V: Support gather_load/scatter RVV auto-vectorization

[Palmer Dabbelt]

On Thu, 13 Jul 2023 07:01:26 PDT (-0700), gcc-patches@gcc.gnu.org wrote:
>
>
> On 7/13/23 01:47, Richard Biener wrote:
>> On Thu, Jul 13, 2023 at 1:30 AM 钟居哲 <juzhe.zh...@rivai.ai> wrote:
>>>
>>> I notice vectorizable_call in Loop Vectorizer.
>>> It's vectorizing CALL function for example like fmax/fmin.
>>>  From my understanding, we dont have RVV instruction for fmax/fmin?

Unless I'm misunderstanding, we do.  The ISA manual says

    === Vector Floating-Point MIN/MAX Instructions
    
    The vector floating-point `vfmin` and `vfmax` instructions have the
    same behavior as the corresponding scalar floating-point instructions
    in version 2.2 of the RISC-V F/D/Q extension: they perform the 
`minimumNumber`
    or `maximumNumber` operation on active elements.
    
    ----
        # Floating-point minimum
        vfmin.vv vd, vs2, vs1, vm   # Vector-vector
        vfmin.vf vd, vs2, rs1, vm   # vector-scalar
    
        # Floating-point maximum
        vfmax.vv vd, vs2, vs1, vm   # Vector-vector
        vfmax.vf vd, vs2, rs1, vm   # vector-scalar
    ----

so we should be able to match at least some loops.

>>
>> There's things like .POPCOUNT which we can vectorize, but sure, it
>> depends on the ISA if there's anything.
> Right.  And RV has some of these -- vcpop, vfirst...  Supporting them
> obviously isn't a requirement for a vector implementation, but they're
> nice to have :-)
>
> Jeff