[cfe-dev] Question on Clang OpenCL to SPIR Compilation

[Andrew Gozillon via cfe-dev]

Hi Alastair,


I thought that might be the case (after reading around a bit), but was unsure due to the documentation and wanted to be certain.


Thank you very much for the quick and useful reply, looks like I'll be using the Khronos SPIR compiler for all my SPIR needs then.


Best Regards,

Andrew Gozillon

________________________________
From: Alastair Murray <alastair.murray at codeplay.com>
Sent: 08 March 2017 17:51:34
To: Andrew Gozillon
Cc: cfe-dev at lists.llvm.org
Subject: Re: [cfe-dev] Question on Clang OpenCL to SPIR Compilation


Hi Andrew,

On 08/03/17 17:07, Andrew Gozillon via cfe-dev wrote:

Hi guys,


I've been trying to get Clang 5.0 to compile a very simple OpenCL kernel example to SPIR (1.2) so that I can run it through another program that basically loads the SPIR binary and executes it.


However I've been having some issues in that the program loads up the binary fine and executes it getting the wrong result. Now I don't believe this is an issue with the program that loads the binary or the OpenCL kernel itself for a couple of reasons 1) Is that I can compile the OpenCL kernel to SPIR using the Intel Offline Compiler and the Khronos SPIR compiler (based off of Clang/LLVM 3.3) and the returned SPIR binary will run through the program and output as expected and 2) I can just run the OpenCL code through it and output the compiled binary and then run that binary back through and get the correct results.



So at the moment I'm unsure if this is to do with the compile command I'm giving to Clang is slightly off or if the output llvm from Clang 5.0 no longer supports SPIR 1.0/1.2 (although the Clang 5 documentation leads me to believe it does still support it)?

The bitcode emitted by a modern Clang is not strictly SPIR, even when setting the spir64-unknown-unknown triple.  It is not intended to be SPIR either, i.e. this is not a bug.  LLVM IR has changed since the SPIR specification was written.  If you want to produce valid SPIR that an OpenCL driver will consume you should use something like the Khronos SPIR generator that you already mentioned.

However, some drivers will actually consume bitcode like you are producing as if it were SPIR, but only up to the version of Clang/LLVM that there are built using (if they are built using Clang/LLVM).  So it is unlikely to work when producing bitcode from a tip Clang/LLVM, but may still work for something newer than 3.2.  This is because newer versions of LLVM can consume older bitcode files (SPIR), but cannot produce them.

Regards,
Alastair Murray.



The compiler command I'm feeding to Clang at the moment is:

clang -cc1 -isystem $LIBCLC/generic/include -include clc/clc.h -Dcl_clang_storage_class_specifiers -triple spir64-unknown-unknown -x cl -cl-std=CL1.2 -emit-llvm -o $NAME.ll $NAME.cl

Although I've tried a number of variations from the documentation with no luck.


Thank you very much for your time, and help with this matter.


Best Regards,

Andrew Gozillon


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Alastair Murray
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Please consider the environment and think before you print.

The University of the West of Scotland is a registered Scottish charity. Charity number SC002520.

This e-mail and any attachment is for authorised use by the intended recipient(s) only. It may contain proprietary material, confidential information and/or be subject to legal privilege. It should not be copied, disclosed to, retained or used by, any other party. If you are not an intended recipient then please promptly delete this e-mail and any attachment and all copies and inform the sender.

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