https://llvm.org/bugs/show_bug.cgi?id=31041
Bug ID: 31041
Summary: Unhelpful error and inconsistent behavior with "clang
-E -o" and "clang -S -o" when compiling CUDA code
Product: clang
Version: unspecified
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: CUDA
Assignee: unassignedclangb...@nondot.org
Reporter: justin.le...@gmail.com
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
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?
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