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

[Wangnan (F)]

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@xxxxxxxxxx>
> ...
> > +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.