llvm dev - Feb 2017 - Clang 5.0 support for armv8 64 bit with neon and auto vectorization

Hi there,

I am Software product developer at Robert Bosch, Germany.

We are using armv8 64bit targets for our development. We have the need to do the
cross compiling for our target on windows. I have compiled clang 5.0 from the
vcs git. I have tried compiling the code with following options set:

clang.exe -target armv8 -fslp-vectorize-aggressive  -mfpu=neon -mfloat-abi=hard
-c test.cpp

As you can see in the options, we require neon feature as well as auto
vectorizations on armv8 (64 bit). Can you tell me that is it true that clang
supports neon and auto vectorizations with 64bit arm v8 architecture?

This setting says that neon is not in support, Can you explain why? As of my
understanding, arm v8 is a 64 bit architecture!
clang.exe -target arm64 -fslp-vectorize-aggressive  -mfpu=neon -mfloat-abi=hard
-c test.cpp


Mit freundlichen Grüßen / Best regards

Zeeshan Haider

Chassis Systems Control, Engineering Software Coordination, Software Mainstream
Management, Methods Group 1 (CC/ESM1)
Robert Bosch GmbH | Postfach 16 61 | 71226 Leonberg | GERMANY |
www.bosch.com<http://www.bosch.com/>
Tel. +49(711)811-47379 | Fax +49(711)811-0 | Zeeshan.Haider at
de.bosch.com<mailto:Zeeshan.Haider at de.bosch.com>

Sitz: Stuttgart, Registergericht: Amtsgericht Stuttgart, HRB 14000;
Aufsichtsratsvorsitzender: Franz Fehrenbach; Geschäftsführung: Dr. Volkmar
Denner,
Dr. Stefan Asenkerschbaumer, Dr. Rolf Bulander, Dr. Stefan Hartung, Dr. Markus
Heyn, Dr. Dirk Hoheisel,
Christoph Kübel, Uwe Raschke, Dr. Werner Struth, Peter Tyroller

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Hello Haider,

I'll have to make this quick as I need to leave the office to get on a
train. I hope my colleagues will be able to correct anything I've got
wrong.

I suggest taking a look at the set of command line options supported
by the aarch64 target. The armv8 target can mean m-profile without
ARM, r-profile or a-profile, floating point or neon is not uniform
across these targets.

For -target=aarch64 simd and hard precision floating point are the
default and assumed option, there is also no ABI support for
soft-floating point so the command line options are redundant. I
suggest just removing -mfpu and -mfloat-abi and you'll get the results
you want.

The -march and -mcpu options can give you some extra control, for
example --target=aarch64 -march=armv8-a+simd+fp.

Peter



On 3 February 2017 at 08:48, Haider Zeeshan (CC/ESM1) via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> Hi there,
>
>
>
> I am Software product developer at Robert Bosch, Germany.
>
>
>
> We are using armv8 64bit targets for our development. We have the need to
do
> the cross compiling for our target on windows. I have compiled clang 5.0
> from the vcs git. I have tried compiling the code with following options
> set:
>
>
>
> clang.exe -target armv8 -fslp-vectorize-aggressive  -mfpu=neon
> -mfloat-abi=hard -c test.cpp
>
>
>
> As you can see in the options, we require neon feature as well as auto
> vectorizations on armv8 (64 bit). Can you tell me that is it true that
clang
> supports neon and auto vectorizations with 64bit arm v8 architecture?
>
>
>
> This setting says that neon is not in support, Can you explain why? As of
my
> understanding, arm v8 is a 64 bit architecture!
>
> clang.exe -target arm64 -fslp-vectorize-aggressive  -mfpu=neon
> -mfloat-abi=hard -c test.cpp
>
>
>
>
>
> Mit freundlichen Grüßen / Best regards
>
> Zeeshan Haider
>
>
>
> Chassis Systems Control, Engineering Software Coordination, Software
> Mainstream Management, Methods Group 1 (CC/ESM1)
>
> Robert Bosch GmbH | Postfach 16 61 | 71226 Leonberg | GERMANY |
> www.bosch.com
>
> Tel. +49(711)811-47379 | Fax +49(711)811-0 | Zeeshan.Haider at de.bosch.com
>
>
>
> Sitz: Stuttgart, Registergericht: Amtsgericht Stuttgart, HRB 14000;
>
> Aufsichtsratsvorsitzender: Franz Fehrenbach; Geschäftsführung: Dr. Volkmar
> Denner,
>
> Dr. Stefan Asenkerschbaumer, Dr. Rolf Bulander, Dr. Stefan Hartung, Dr.
> Markus Heyn, Dr. Dirk Hoheisel,
>
> Christoph Kübel, Uwe Raschke, Dr. Werner Struth, Peter Tyroller
>
>
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>

On 3 February 2017 at 00:48, Haider Zeeshan (CC/ESM1) via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> clang.exe -target armv8 -fslp-vectorize-aggressive  -mfpu=neon
> -mfloat-abi=hard -c test.cpp
Peter's advice is good (-mfpu and -mfloat-abi aren't needed). But also
note that "-target armv8" actually targets 32-bit ARM (v8 CPUs usually
support both modes).

You probably want to specify a full triple for the target, maybe
"-target aarch64-linux-gnu", otherwise the OS part might default to
Windows since that's where you're running. Clang doesnn't support
Windows on AArch64.

Cheers.

Tim.

Thanks Peter and Tim.

Being that said, can I be sure that for 64 bit arm architectures (e.g. arm
cortex A57) the  neon feature and auto-vectorization is supported as default by
clang 5.0?

Because for us these two features are deal breaking for compiler evaluation.

Mit freundlichen Grüßen / Best regards 

Zeeshan Haider

Chassis Systems Control, Engineering Software Coordination, Software Mainstream
Management, Methods Group 1 (CC/ESM1)
Robert Bosch GmbH | Postfach 16 61 | 71226 Leonberg | GERMANY | www.bosch.com
Tel. +49(711)811-47379 | Fax +49(711)811-0 | Zeeshan.Haider at de.bosch.com

Sitz: Stuttgart, Registergericht: Amtsgericht Stuttgart, HRB 14000;
Aufsichtsratsvorsitzender: Franz Fehrenbach; Geschäftsführung: Dr. Volkmar
Denner,
Dr. Stefan Asenkerschbaumer, Dr. Rolf Bulander, Dr. Stefan Hartung, Dr. Markus
Heyn, Dr. Dirk Hoheisel,
Christoph Kübel, Uwe Raschke, Dr. Werner Struth, Peter Tyroller


-----Original Message-----
From: Tim Northover [mailto:t.p.northover at gmail.com] 
Sent: Freitag, 3. Februar 2017 16:02
To: Haider Zeeshan (CC/ESM1) <Zeeshan.Haider at de.bosch.com>
Cc: llvm-dev at lists.llvm.org
Subject: Re: [llvm-dev] Clang 5.0 support for armv8 64 bit with neon and auto
vectorization

On 3 February 2017 at 00:48, Haider Zeeshan (CC/ESM1) via llvm-dev <llvm-dev
at lists.llvm.org> wrote:
> clang.exe -target armv8 -fslp-vectorize-aggressive  -mfpu=neon 
> -mfloat-abi=hard -c test.cpp
Peter's advice is good (-mfpu and -mfloat-abi aren't needed). But also
note that "-target armv8" actually targets 32-bit ARM (v8 CPUs usually
support both modes).

You probably want to specify a full triple for the target, maybe "-target
aarch64-linux-gnu", otherwise the OS part might default to Windows since
that's where you're running. Clang doesnn't support Windows on
AArch64.

Cheers.

Tim.