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On 23.10.18 01:42, Artem Belevich wrote:<br>
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<div dir="ltr">On Mon, Oct 22, 2018 at 5:45 AM Lorenz Braun
via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org"
moz-do-not-send="true">llvm-dev@lists.llvm.org</a>>
wrote:<br>
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<blockquote class="gmail_quote" style="margin:0px 0px 0px
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rgb(204,204,204);padding-left:1ex">Hi,<br>
<br>
i just found out that i can use llc to also produce ptx
assembly for <br>
GPUs. I noticed that the produced ptx assembly seems to be
targeted at <br>
the gpu architecture sm_20 by default.<br>
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<div class="gmail_default"
style="font-family:verdana,sans-serif">This is currently
the default CPU type for NVPTX back-end.</div>
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<br>
Is there a way to explicitly demand different or
additional target <br>
architectures like sm_30 for example?<br>
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style="font-family:verdana,sans-serif">It works the same
way as for the other back-ends. You specify the CPU
variant with -mcpu=. E.g. for sm_30 you should use <span
style="font-family:Arial,Helvetica,sans-serif">-mcpu=sm_30</span></div>
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-mcpu=sm_30 was just what i was looking for. Thank you very much!
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cite="mid:CA+wKYkOAF16OV+3SMAntta=N1rvAxMy83L526m3_W3Yj5DwMZw@mail.gmail.com">
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<br>
When i compile a cuda kernel with gpu arch. sm_30 using
clang++ the <br>
.target directive in the ptx assembly will be set to
sm_30. However when <br>
i save the bitcode of the same compilation and hand it to
llc the <br>
.target directive is sm_20. There is an attribute in the
bitcode that <br>
say "target-cpu"="sm_30". The information that sm_30 is
required is <br>
still there. </blockquote>
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style="font-family:verdana,sans-serif">It's a *function*
attribute which, generally speaking, can't be used as
the default for the whole module. It also does not do
much in NVPTX back-end. Eventually it will be used to
enforce that -mcpu=XXX is the same or higher than the
all target-cpu attributes in a module. This is one of
the areas where NVPTX can't implement what the attribute
was intended to do -- target different CPU variants
within the same module. It's doable on x86 where the
same ISA can represent instructions for different CPU
variants, but can't be done in PTX which requires
everything in the module to be for the same GPU.</div>
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Thanks for the info. I understand, when having multiple functions
with different target-cpus this can only done in multiple modules.
But i think use cases for this are rather rare.<br>
<br>
Best regards<br>
Lorenz<br>
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