llvm dev - Aug 2017 - Status of llvm.experimental.vector.reduce.* intrinsics

Hi Amara,

thank you for the clarification. I tested the intrinsics x86_64 and it
seemed to work pretty well. Looking forward to try this intrinsics with
the AArch64 backend. Maybe I find the time to look into codegen to get
this intrinsics out of experimental stage. They seem pretty useful.

Cheers,
Michael

-----Original Message-----
From: Amara Emerson [amara.emerson at gmail.com]
Received: Donnerstag, 03 Aug. 2017, 14:50
To: michael.haidl at uni-muenster.de [michael.haidl at uni-muenster.de]
CC: llvm-dev at lists.llvm.org [llvm-dev at lists.llvm.org]
Subject: Re: [llvm-dev] Status of llvm.experimental.vector.reduce.* intrinsics

​Hi Michael,

​The intrinsics are still technically in an experimental state as we need to
have a further discussion to build consensus before marking them as fully
supported.

The AArch64 backend has been using them for all *natively supported* vector
reductions for a few months now, with no issues as far as I'm aware. There
are some rough edges which need some further work. For example, we're
currently relying on a TTI hook to determine whether or not we create an
intrinsic call or degenerate into a shuffevector sequence based on the reduction
type. This was intended as a transitional stage. To mark the intrinsics as being
first class operations we probably need to add support in codegen to expand the
VECREDUCE_* nodes into the shufflevector reduction pattern, so that targets can
generate the intrinsics in all cases without having to rely on TTI.

Amara


On 3 August 2017 at 12:03, Haidl, Michael via llvm-dev <llvm-dev at
lists.llvm.org<mailto:llvm-dev at lists.llvm.org>> wrote:
Hi,

I was wandering about the status of the
llvm.experimental.vector.reduce.* intrinsics. Are all back-ends
supporting those intrinsics or are they still in a very "experimental"
state?

Thanks,
Michael
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On 3 August 2017 at 19:48, Haidl, Michael via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> thank you for the clarification. I tested the intrinsics x86_64 and it
> seemed to work pretty well. Looking forward to try this intrinsics with
> the AArch64 backend. Maybe I find the time to look into codegen to get
> this intrinsics out of experimental stage. They seem pretty useful.
In addition to Amara's point, it'd be good to have it working and
default for other architectures before we can move out of experimental
if we indeed intend to make it non-arch-specific (which we do).

So, if you could share your code for the x86 port, that'd be great.
But if you could help with the final touches on the code-gen part,
that'd be awesome.

cheers,
--renato

Hi Renato,

just to make it clear, I didn't implement reductions on x86_64 they just 
worked when I tried to lower an 
llvm.experimentel.vector.reduce.or.i1.v8i1 intrinsic. A shuffle pattern 
is generated for the intrinsic.

	vpshufd	$78, %xmm0, %xmm1       # xmm1 = xmm0[2,3,0,1]
	vpor	%xmm1, %xmm0, %xmm0
	vpshufd	$229, %xmm0, %xmm1      # xmm1 = xmm0[1,1,2,3]
	vpor	%xmm1, %xmm0, %xmm0
	vpsrld	$16, %xmm0, %xmm1
	vpor	%xmm1, %xmm0, %xmm0
	vpextrb	$0, %xmm0, %eax


However, on AArche64 I encountered an unreachable where codegen does not 
know how to promote the i1 type. Since I am more familiar with the 
midlevel I have to start digging into codegen. Any hints where to start 
would be awesome.

Cheers,
Michael

Am 04.08.2017 um 08:18 schrieb Renato Golin:
> On 3 August 2017 at 19:48, Haidl, Michael via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
>> thank you for the clarification. I tested the intrinsics x86_64 and it
>> seemed to work pretty well. Looking forward to try this intrinsics with
>> the AArch64 backend. Maybe I find the time to look into codegen to get
>> this intrinsics out of experimental stage. They seem pretty useful.
> 
> In addition to Amara's point, it'd be good to have it working and
> default for other architectures before we can move out of experimental
> if we indeed intend to make it non-arch-specific (which we do).
> 
> So, if you could share your code for the x86 port, that'd be great.
> But if you could help with the final touches on the code-gen part,
> that'd be awesome.
> 
> cheers,
> --renato
>