[llvm-dev] sum elements in the vector

Mon May 30 08:04:40 PDT 2016

Hi Rail,

An additional suggestion w.r.t your example code :

int a[] = {1, 2, 3, 4};
int sum = 0;
for (int i = 0; i < 4; i++)
  sum+= a[i];

This loop can unroll and look something like :

sum += a[0] + a[1] + a[2] + a[3]

You can identify above pattern as well to mark intrinsic for horizontal
addition, keeping FP math option into consideration.

Regards,
Suyog

On Sat, May 28, 2016 at 9:29 AM, suyog sarda <sardask01 at gmail.com> wrote:

> Hi Rail,
>
> Below 2 revisions might be of your interest which Detect SAD patterns and
> emit psadbw instructions on X86.:
>
> http://reviews.llvm.org/D14840
> http://reviews.llvm.org/D14897
>
> Intrinsics related to absdiff revisons :
>
> http://reviews.llvm.org/D10867
> http://reviews.llvm.org/D11678
>
> Hope this helps.
>
> Regards,
> Suyog
>
> On Sat, May 28, 2016 at 4:20 AM, Rail Shafigulin via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> Hi Shahid.
>>
>> Do you mind providing a concrete example of X86 code where an intrinsic
>> was added (preferrable with filenames and line numbers)? I'm having
>> difficulty tracking down the steps you provided.
>>
>> Any help is appreciated.
>>
>>
>> On Mon, Apr 4, 2016 at 9:02 PM, Shahid, Asghar-ahmad <
>> Asghar-ahmad.Shahid at amd.com> wrote:
>>
>>> Hi Rail,
>>>
>>>
>>>
>>> We had done this for generation of X86 PSAD (sum of absolute difference)
>>> instruction through
>>>
>>> Llvm intrinsic. Doing this requires following
>>>
>>> 1.       Define an intrinsic, xyz(),  for the required instruction and
>>> corresponding SDNode
>>>
>>> 2.       Generate the “call xyz() “ IR based the matched pattern
>>>
>>> 3.       Map “call xyz()” IR to corresponding SDNode in
>>> SelectionDagBuilder.cpp
>>>
>>> 4.       Provide default expansion of the xyz() intrinsic
>>>
>>> 5.       Legalize type and/or operation
>>>
>>> 6.       Provide Lowering of intrinsic/SDNode to generate your target
>>> instruction
>>>
>>>
>>>
>>> You can visit http://llvm.org/docs/ExtendingLLVM.html for details.
>>>
>>>
>>>
>>> Regards,
>>>
>>> Shahid
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>> *From:* llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] *On Behalf Of
>>> *Rail Shafigulin via llvm-dev
>>> *Sent:* Monday, April 04, 2016 11:00 PM
>>> *To:* Das, Dibyendu
>>> *Cc:* llvm-dev at lists.llvm.org
>>> *Subject:* Re: [llvm-dev] sum elements in the vector
>>>
>>>
>>>
>>> Thanks for the pointers. I looked at hadd instructions. They seem to do
>>> very similar to what I need. Unfortunately as I said before my LLVM
>>> experience is limited. My understanding is that when I create a new type of
>>> SDNode I need to specify a pattern for it, so that when LLVM is analyzing
>>> the code and is seeing a given pattern it would create this particular
>>> node. I'm really struggling to understand how it is done. So here are the
>>> problems that I'm having.
>>>
>>>
>>>
>>> 1. How do I identify that pattern that should be used?
>>>
>>> 2. How do I specify a given pattern?
>>>
>>>
>>>
>>> Do you (or someone else) mind helping me out?
>>>
>>>
>>>
>>> Any help is appreciated.
>>>
>>>
>>>
>>> On Mon, Apr 4, 2016 at 9:59 AM, Das, Dibyendu <Dibyendu.Das at amd.com>
>>> wrote:
>>>
>>> This is roughly along the lines of x86 hadd* instructions though the
>>> semantics of hadd* may not exactly match what you are looking for. This is
>>> probably more in line with x86/ARM SAD-like instructions but I don’t think
>>> llvm generates SAD without intrinsics.
>>>
>>>
>>>
>>> *From:* llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] *On Behalf Of
>>> *Rail Shafigulin via llvm-dev
>>> *Sent:* Monday, April 04, 2016 9:34 AM
>>> *To:* llvm-dev <llvm-dev at lists.llvm.org>
>>> *Subject:* [llvm-dev] sum elements in the vector
>>>
>>>
>>>
>>> My target has an instruction that adds up all elements in the vector and
>>> stores the result in a register. I'm trying to implement it in my compiler
>>> but I'm not sure even where to start.
>>>
>>>
>>>
>>> I did look at other targets, but they don't seem to have anything like
>>> it ( I could be wrong. My experience with LLVM is limited, so if I missed
>>> it, I'd appreciate if someone could point it out ).
>>>
>>>
>>>
>>> My understanding is that if SDNode for such an instruction doesn't exist
>>> I have to define one. Unfortunately, I don't know how to do it. I don't
>>> even know where to start looking. Would someone care to point me in the
>>> right direction?
>>>
>>>
>>>
>>> Any help is appreciated.
>>>
>>>
>>>
>>> --
>>>
>>> Rail Shafigulin
>>>
>>> Software Engineer
>>> Esencia Technologies
>>>
>>>
>>>
>>>
>>>
>>> --
>>>
>>> Rail Shafigulin
>>>
>>> Software Engineer
>>> Esencia Technologies
>>>
>>
>>
>>
>> --
>> Rail Shafigulin
>> Software Engineer
>> Esencia Technologies
>>
>> On Mon, Apr 4, 2016 at 9:02 PM, Shahid, Asghar-ahmad <
>> Asghar-ahmad.Shahid at amd.com> wrote:
>>
>>> Hi Rail,
>>>
>>>
>>>
>>> We had done this for generation of X86 PSAD (sum of absolute difference)
>>> instruction through
>>>
>>> Llvm intrinsic. Doing this requires following
>>>
>>> 1.       Define an intrinsic, xyz(),  for the required instruction and
>>> corresponding SDNode
>>>
>>> 2.       Generate the “call xyz() “ IR based the matched pattern
>>>
>>> 3.       Map “call xyz()” IR to corresponding SDNode in
>>> SelectionDagBuilder.cpp
>>>
>>> 4.       Provide default expansion of the xyz() intrinsic
>>>
>>> 5.       Legalize type and/or operation
>>>
>>> 6.       Provide Lowering of intrinsic/SDNode to generate your target
>>> instruction
>>>
>>>
>>>
>>> You can visit http://llvm.org/docs/ExtendingLLVM.html for details.
>>>
>>>
>>>
>>> Regards,
>>>
>>> Shahid
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>> *From:* llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] *On Behalf Of
>>> *Rail Shafigulin via llvm-dev
>>> *Sent:* Monday, April 04, 2016 11:00 PM
>>> *To:* Das, Dibyendu
>>> *Cc:* llvm-dev at lists.llvm.org
>>> *Subject:* Re: [llvm-dev] sum elements in the vector
>>>
>>>
>>>
>>> Thanks for the pointers. I looked at hadd instructions. They seem to do
>>> very similar to what I need. Unfortunately as I said before my LLVM
>>> experience is limited. My understanding is that when I create a new type of
>>> SDNode I need to specify a pattern for it, so that when LLVM is analyzing
>>> the code and is seeing a given pattern it would create this particular
>>> node. I'm really struggling to understand how it is done. So here are the
>>> problems that I'm having.
>>>
>>>
>>>
>>> 1. How do I identify that pattern that should be used?
>>>
>>> 2. How do I specify a given pattern?
>>>
>>>
>>>
>>> Do you (or someone else) mind helping me out?
>>>
>>>
>>>
>>> Any help is appreciated.
>>>
>>>
>>>
>>> On Mon, Apr 4, 2016 at 9:59 AM, Das, Dibyendu <Dibyendu.Das at amd.com>
>>> wrote:
>>>
>>> This is roughly along the lines of x86 hadd* instructions though the
>>> semantics of hadd* may not exactly match what you are looking for. This is
>>> probably more in line with x86/ARM SAD-like instructions but I don’t think
>>> llvm generates SAD without intrinsics.
>>>
>>>
>>>
>>> *From:* llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] *On Behalf Of
>>> *Rail Shafigulin via llvm-dev
>>> *Sent:* Monday, April 04, 2016 9:34 AM
>>> *To:* llvm-dev <llvm-dev at lists.llvm.org>
>>> *Subject:* [llvm-dev] sum elements in the vector
>>>
>>>
>>>
>>> My target has an instruction that adds up all elements in the vector and
>>> stores the result in a register. I'm trying to implement it in my compiler
>>> but I'm not sure even where to start.
>>>
>>>
>>>
>>> I did look at other targets, but they don't seem to have anything like
>>> it ( I could be wrong. My experience with LLVM is limited, so if I missed
>>> it, I'd appreciate if someone could point it out ).
>>>
>>>
>>>
>>> My understanding is that if SDNode for such an instruction doesn't exist
>>> I have to define one. Unfortunately, I don't know how to do it. I don't
>>> even know where to start looking. Would someone care to point me in the
>>> right direction?
>>>
>>>
>>>
>>> Any help is appreciated.
>>>
>>>
>>>
>>> --
>>>
>>> Rail Shafigulin
>>>
>>> Software Engineer
>>> Esencia Technologies
>>>
>>>
>>>
>>>
>>>
>>> --
>>>
>>> Rail Shafigulin
>>>
>>> Software Engineer
>>> Esencia Technologies
>>>
>>
>>
>>
>> --
>> Rail Shafigulin
>> Software Engineer
>> Esencia Technologies
>>
>> _______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20160530/22516242/attachment-0001.html>