Re: [PATCH v3 10/30] perf clang: Add builtin clang support ant test case

["Wangnan (F)" <wangnan0@huawei.com>]

On 2016/11/27 1:17, Alexei Starovoitov wrote:
> On Sat, Nov 26, 2016 at 07:03:34AM +0000, Wang Nan wrote:
>> Add basic clang support in clang.cpp and test__clang() testcase. The
>> first testcase checks if builtin clang is able to generate LLVM IR.
>>
>> tests/clang.c is a proxy. Real testcase resides in
>> utils/c++/clang-test.cpp in c++ and exports C interface to perf test
>> subsystem.
>>
>> Test result:
>>
>>     $ perf test -v clang
>>     51: Test builtin clang support                               :
>>     51.1: Test builtin clang compile C source to IR              :
>>     --- start ---
>>     test child forked, pid 13215
>>     test child finished with 0
>>     ---- end ----
>>     Test builtin clang support subtest 0: Ok
>>
>> Signed-off-by: Wang Nan <wangnan0@huawei.com>
> ...
>> +static CompilerInvocation *
>> +createCompilerInvocation(StringRef& Path, DiagnosticsEngine& Diags)
>> +{
>> +	llvm::opt::ArgStringList CCArgs {
>> +		"-cc1",
>> +		"-triple", "bpf-pc-linux",
>> +		"-fsyntax-only",
>> +		"-ferror-limit", "19",
>> +		"-fmessage-length", "127",
> why such limits?
>
>> +		"-O2",
>> +		"-nostdsysteminc",
>> +		"-nobuiltininc",
>> +		"-vectorize-loops",
>> +		"-vectorize-slp",

Thank you for pointing these out. These arguments are get by analysising
the clang example:

https://llvm.org/svn/llvm-project/cfe/branches/ggreif/CallInst-operands/examples/clang-interpreter/main.cpp

The above example create a C compiler using clang::driver::Driver (bcc 
also uses driver).
I form the argument list according to arglist the driver created for its CI,
and leaves arguments I'm not quite sure unchanged.

> why above two flags are needed?
>
>> +		"-Wno-unused-value",
>> +		"-Wno-pointer-sign",
> these two -Wno makes sense. please add the comment to explain the reasons.
>
They are inherited from samples/bpf/Makefile to suppress some warning
when include kernel headers.

Thank you.