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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Unhelpful error and inconsistent behavior with "clang -E -o" and "clang -S -o" when compiling CUDA code"
href="https://llvm.org/bugs/show_bug.cgi?id=31041">31041</a>
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<th>Summary</th>
<td>Unhelpful error and inconsistent behavior with "clang -E -o" and "clang -S -o" when compiling CUDA code
</td>
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>unspecified
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>CUDA
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>justin.lebar@gmail.com
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
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<th>Classification</th>
<td>Unclassified
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<p>
<div>
<pre>Without -o, -E does host compilation and prints to stdout:
$ echo 'XXX __CUDA_ARCH__' | llvm-run clang++ -E -x cuda - | grep XXX
XXX __CUDA_ARCH__
(That the __CUDA_ARCH__ macro is not defined indicates that the preprocessed
source is host code, rather than device code.)
But with -o, we raise a confusing error:
$ echo | llvm-run clang++ -E -x cuda - -o -
clang-4.0: error: cannot specify -o when generating multiple output files
The same thing happens with -S, except that -S outputs *device* assembly:
$ echo | llvm-run clang++ -S -x cuda -
$ cat -- '--cuda-nvptx64-nvidia-cuda-sm_20.s'
//
// Generated by LLVM NVPTX Back-End
//
[...]
With -o, we raise the same confusing error:
$ echo | llvm-run clang++ -E -x cuda - -o -
clang-4.0: error: cannot specify -o when generating multiple output files
I can see two ways to rationalize our behavior:
1) Require --cuda-device-only or --cuda-host-only with -E and -S (with and
without -o), and improve the error message to mention these flags.
2) Default -E and -S to either host or device and make things work the same
with -o.
I kind of lean towards (1), but maybe that would break people?</pre>
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