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<div class="moz-cite-prefix">On 09/12/2018 05:21 PM, Matthias Braun
via llvm-dev wrote:<br>
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<div class="">On Sep 12, 2018, at 2:54 PM, Richard Smith via
llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org"
class="" moz-do-not-send="true">llvm-dev@lists.llvm.org</a>>
wrote:</div>
<br class="Apple-interchange-newline">
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<div dir="ltr" class="">On Tue, 11 Sep 2018 at 19:40,
Tom Stellard via llvm-dev <<a
href="mailto:llvm-dev@lists.llvm.org" class=""
moz-do-not-send="true">llvm-dev@lists.llvm.org</a>>
wrote:<br class="">
</div>
<blockquote class="gmail_quote" style="margin: 0px 0px
0px 0.8ex; border-left-width: 1px; border-left-style:
solid; border-left-color: rgb(204, 204, 204);
padding-left: 1ex;">On 09/11/2018 12:50 PM, Richard
Smith via llvm-dev wrote:<br class="">
> On Mon, 10 Sep 2018 at 18:47, Nicholas Wilson via
llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org"
target="_blank" class="" moz-do-not-send="true">llvm-dev@lists.llvm.org</a><span
class="Apple-converted-space"> </span><mailto:<a
href="mailto:llvm-dev@lists.llvm.org"
target="_blank" class="" moz-do-not-send="true">llvm-dev@lists.llvm.org</a>>>
wrote:<br class="">
><span class="Apple-converted-space"> </span><br
class="">
> I was going to wait until Neil Trevett got
back to me about becoming a SPIR-V TSG advisor but
this seems like just as good an opportunity. Please
see the previous discussion [1] if you have not
already, there were many relevant points made.<br
class="">
><span class="Apple-converted-space"> </span><br
class="">
> First, I’d like to note that while clang may
be the primary motivator for many of the readers here
it is not the only frontend that would like to make
use of proper SPIR-V support in LLVM. In particular,
the current implementation of builtins as Itanium with
extensions mangled C++ is much more difficult to use
(even if those frontends have a C++ mangler, the
extensions make it unusable), compared to intrinsics
which is _the_ way backends for LLVM expose builtins.
This is an absolute requirement for me for SPIR-V
support in upstream LLVM.<br class="">
><span class="Apple-converted-space"> </span><br
class="">
> I’d much rather have this as a target than as
an external library, but if it means I get intrinsics
faster then I’m all for it.<br class="">
><span class="Apple-converted-space"> </span><br
class="">
><span class="Apple-converted-space"> </span><br
class="">
> +1. What would be the justification for using an
external binary for this rather than treating it like
any other LLVM backend?<br class="">
><span class="Apple-converted-space"> </span><br
class="">
<br class="">
This has been discussed in the past, but I don't think
SPIR-V<br class="">
is a good fit for an LLVM backend. It is very similar
to LLVM<br class="">
IR and it seems like overkill to write a whole backend
just to<br class="">
do a simple translation.</blockquote>
<div class=""><br class="">
</div>
<div class="">
<div class="">I don't see how SPIR-V is any different
from WebAssembly or PTXAS in this regard. I also
don't see why a "whole backend" is a different
amount of work from a separate program that
implements a whole backend.</div>
</div>
</div>
</div>
</div>
</blockquote>
<div>Using lib/CodeGen and going to MIR makes sense if you have
to solve instruction selection, legalization, scheduling,
register/resource allocation problems, manage a callstack etc.
if you don't need any (or most) of that then I think it makes
sense to just build a custom IR pass rather than invoking the
whole codegen machinery.</div>
<br class="">
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<div class="">
<div class=""> <br class="">
</div>
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solid; border-left-color: rgb(204, 204, 204);
padding-left: 1ex;">Not to mention the fact that I
don't<br class="">
see how it's possible with the current backend
infrastructure<br class="">
to preserve type information for complex types like
structs all<br class="">
the way through the codegen pipeline.<br class="">
</blockquote>
<div class=""><br class="">
</div>
<div class="">The nice thing about code is that it's
malleable. If there's a limitation that prevents
SPIR-V being written as an LLVM target, we should just
fix that.</div>
</div>
</div>
</div>
</blockquote>
<div>Indeed we should still be able to implement the
TargetMachine interface and get the thing into the
TargetMachine registry.</div>
</div>
</blockquote>
<br>
I agree. Isn't this the way that the C backend used to work?<br>
<br>
-Hal<br>
<br>
<blockquote type="cite"
cite="mid:870D6C95-C682-42E4-B22B-FCFAB2AF4C28@apple.com">
<div>
<div><br class="">
</div>
<div>- Matthias</div>
<br class="">
<blockquote type="cite" class="">
<div class="">
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<div class=""><br class="">
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padding-left: 1ex;">-Tom<br class="">
<br class="">
<br class="">
><span class="Apple-converted-space"> </span><br
class="">
> Could you please link the thread mentioned?<br
class="">
><span class="Apple-converted-space"> </span><br
class="">
> Thanks,<br class="">
> Nic<br class="">
><span class="Apple-converted-space"> </span><br
class="">
> P.S. Feel free to use the tablegen
descriptions of the SPIR-V format from [2]<br class="">
><span class="Apple-converted-space"> </span><br
class="">
> [1]:<span class="Apple-converted-space"> </span><a
href="http://lists.llvm.org/pipermail/llvm-dev/2017-May/112538.html"
rel="noreferrer" target="_blank" class=""
moz-do-not-send="true">http://lists.llvm.org/pipermail/llvm-dev/2017-May/112538.html</a><br
class="">
> [2]:<span class="Apple-converted-space"> </span><a
href="https://github.com/thewilsonator/llvm-target-spirv"
rel="noreferrer" target="_blank" class=""
moz-do-not-send="true">https://github.com/thewilsonator/llvm-target-spirv</a><span
class="Apple-converted-space"> </span><br class="">
><span class="Apple-converted-space"> </span><br
class="">
>> On 10 Sep 2018, at 11:10 pm, Anastasia
Stulova via llvm-dev <<a
href="mailto:llvm-dev@lists.llvm.org"
target="_blank" class="" moz-do-not-send="true">llvm-dev@lists.llvm.org</a><span
class="Apple-converted-space"> </span><mailto:<a
href="mailto:llvm-dev@lists.llvm.org"
target="_blank" class="" moz-do-not-send="true">llvm-dev@lists.llvm.org</a>>>
wrote:<br class="">
>><br class="">
>> Hello,<br class="">
>><br class="">
>> Since 2015 Khronos has switched to the
new portable intermediate format SPIR-V, which has
replaced the original SPIR. The advantage is that it
offers higher portability across different toolchains.
There was a talk about it at a Dev Meeting:<br
class="">
>> <a
href="http://llvm.org/devmtg/2017-03//2017/02/20/accepted-sessions.html#17"
rel="noreferrer" target="_blank" class=""
moz-do-not-send="true">http://llvm.org/devmtg/2017-03//2017/02/20/accepted-sessions.html#17</a><br
class="">
>><br class="">
>> LLVM currently only supports SPIR format
for OpenCL in Clang. Several Khronos vendors (ARM,
AMD, Intel, Xilinx, Codeplay and others) are
interested in adding support for SPIR-V, which should
gradually replace the old SPIR once products are no
longer shipped with the old format. Here is the
detailed description:<br class="">
>> <a
href="https://github.com/KhronosGroup/SPIRV-LLVM-Translator/wiki/SPIRV-Toolchain-for-Clang"
rel="noreferrer" target="_blank" class=""
moz-do-not-send="true">https://github.com/KhronosGroup/SPIRV-LLVM-Translator/wiki/SPIRV-Toolchain-for-Clang</a><br
class="">
>><br class="">
>> To summarize, the idea is to add a SPIR-V
target triple to Clang that can be used to generate a
SPIR-V binary for OpenCL code. There was a separate
thread regarding generation of SPIR-V binary and the
community suggested that a translator from LLVM IR to
SPIR-V can be used as an external tool, called
llvm-spirv. This can be invoked similar to such tools
as ptxas and fatbinary for the CUDA toolchain:<br
class="">
>> <a
href="http://lists.llvm.org/pipermail/llvm-dev/2018-February/121440.html"
rel="noreferrer" target="_blank" class=""
moz-do-not-send="true">http://lists.llvm.org/pipermail/llvm-dev/2018-February/121440.html</a><br
class="">
>><br class="">
>> An example of how Clang can be used to
target SPIR-V:<br class="">
>><br class="">
>> clang -c<span
class="Apple-converted-space"> </span><a
href="http://test.cl/" rel="noreferrer"
target="_blank" class="" moz-do-not-send="true">test.cl</a><span
class="Apple-converted-space"> </span><<a
href="http://test.cl/" rel="noreferrer"
target="_blank" class="" moz-do-not-send="true">http://test.cl</a>>
-target spirv[32|64]-unknown-unknown -o test.spv<br
class="">
>><br class="">
>> This will result in the following Clang
actions:<br class="">
>><br class="">
>> (1) clang -cc1 -triple
spirv[32|64]-unknown-unknown<span
class="Apple-converted-space"> </span><a
href="http://test.cl/" rel="noreferrer"
target="_blank" class="" moz-do-not-send="true">test.cl</a><span
class="Apple-converted-space"> </span><<a
href="http://test.cl/" rel="noreferrer"
target="_blank" class="" moz-do-not-send="true">http://test.cl</a>>
-emit-llvm-bc -o test.bc<br class="">
>><br class="">
>> (2) llvm-spirv test.bc -o test.spv<br
class="">
>><br class="">
>> SPIR-V generation is essential for
completion of OpenCL C++ support in Clang, as newer
OpenCL standards require frontend invocation to be
performed offline, producing the SPIR-V binary that
can be then loaded at application execution time.
Besides that, it will also allow Clang to be used as a
complete standalone tool to generate portable binaries
that can then be consumed by different proprietary
toolchains. In addition, this will open a path to the
LLVM backends for various languages and frontends that
already generate SPIR-V.<br class="">
>><br class="">
>> A more detailed explanation of the
complete design proposal is given in this Wiki page:<br
class="">
>> <a
href="https://github.com/KhronosGroup/SPIRV-LLVM-Translator/wiki/SPIRV-Toolchain-for-Clang"
rel="noreferrer" target="_blank" class=""
moz-do-not-send="true">https://github.com/KhronosGroup/SPIRV-LLVM-Translator/wiki/SPIRV-Toolchain-for-Clang</a><br
class="">
>><br class="">
>> Looking forward to any feedback about the
proposal or possible collaborations,<br class="">
>><br class="">
>> Thanks!<br class="">
>><br class="">
>> Anastasia<br class="">
>>
_______________________________________________<br
class="">
>> LLVM Developers mailing list<br class="">
>> <a href="mailto:llvm-dev@lists.llvm.org"
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target="_blank" class="" moz-do-not-send="true">llvm-dev@lists.llvm.org</a>><br
class="">
>> <a
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class="">
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class="">
>
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> _______________________________________________<br
class="">
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<pre class="moz-signature" cols="72">--
Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory</pre>
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