Re: [PATCH 1/3] vect: Pass stmt_vec_info to TARGET_SIMD_CLONE_USABLE

["Andre Vieira (lists)" <andre.simoesdiasvieira@arm.com>]

On 31/01/2024 13:58, Richard Biener wrote:
> On Wed, 31 Jan 2024, Andre Vieira (lists) wrote:
> 
>>
>>
>> On 31/01/2024 12:13, Richard Biener wrote:
>>> On Wed, 31 Jan 2024, Richard Biener wrote:
>>>
>>>> On Tue, 30 Jan 2024, Andre Vieira wrote:
>>>>
>>>>>
>>>>> This patch adds stmt_vec_info to TARGET_SIMD_CLONE_USABLE to make sure the
>>>>> target can reject a simd_clone based on the vector mode it is using.
>>>>> This is needed because for VLS SVE vectorization the vectorizer accepts
>>>>> Advanced SIMD simd clones when vectorizing using SVE types because the
>>>>> simdlens
>>>>> might match.  This will cause type errors later on.
>>>>>
>>>>> Other targets do not currently need to use this argument.
>>>>
>>>> Can you instead pass down the mode?
>>>
>>> Thinking about that again the cgraph_simd_clone info in the clone
>>> should have sufficient information to disambiguate.  If it doesn't
>>> then we should amend it.
>>>
>>> Richard.
>>
>> Hi Richard,
>>
>> Thanks for the review, I don't think cgraph_simd_clone_info is the right place
>> to pass down this information, since this is information about the caller
>> rather than the simdclone itself. What we are trying to achieve here is making
>> the vectorizer being able to accept or reject simdclones based on the ISA we
>> are vectorizing for. To distinguish between SVE and Advanced SIMD ISAs we use
>> modes, I am also not sure that's ideal but it is what we currently use. So to
>> answer your earlier question, yes I can also pass down mode if that's
>> preferable.
> 
> Note cgraph_simd_clone_info has simdlen and we seem to check elsewhere
> whether that's POLY or constant.  I wonder how aarch64_sve_mode_p
> comes into play here which in the end classifies VLS SVE modes as
> non-SVE?
> 

Using -msve-vector-bits=128
(gdb) p TYPE_MODE (STMT_VINFO_VECTYPE (stmt_vinfo))
$4 = E_VNx4SImode
(gdb) p  TYPE_SIZE (STMT_VINFO_VECTYPE (stmt_vinfo))
$5 = (tree) 0xfffff741c1b0
(gdb) p debug (TYPE_SIZE (STMT_VINFO_VECTYPE (stmt_vinfo)))
128
(gdb) p aarch64_sve_mode_p (TYPE_MODE (STMT_VINFO_VECTYPE (stmt_vinfo)))
$5 = true

and for reference without vls codegen:
(gdb) p TYPE_MODE (STMT_VINFO_VECTYPE (stmt_vinfo))
$1 = E_VNx4SImode
(gdb) p  debug (TYPE_SIZE (STMT_VINFO_VECTYPE (stmt_vinfo)))
POLY_INT_CST [128, 128]

Having said that I believe that the USABLE targethook implementation for 
aarch64 should also block other uses, like an Advanced SIMD mode being 
used as input for a SVE VLS SIMDCLONE. The reason being that for 
instance 'half' registers like VNx2SI are packed differently from V2SI.

We could teach the vectorizer to support these of course, but that 
requires more work and is not extremely useful just yet. I'll add the 
extra check that to the patch once we agree on how to pass down the 
information we need. Happy to use either mode, or stmt_vec_info and 
extract the mode from it like it does now.

>> Regards,
>> Andre
>>
>