[Driver] -noprofilelib flag

[phosek]

Summary

This flag is analoguous to other flags like -nostdlib or -nolibc
and could be used to disable linking of profile runtime library.
This is useful in certain environments like kernel, where profile
instrumentation is still desirable, but we cannot use the standard
runtime library.

[davidxl]

lgtm

[smeenai]

LGTM

[kimgr]

On the fuzzer side, there's also -fsanitize=fuzzer-no-link (see http://llvm.org/docs/LibFuzzer.html#fuzzer-usage). Maybe it would be nice to harmonize all these?

clang/docs/ClangCommandLineReference.rst

 .. option:: -nolibc
 
 .. option:: -nomultidefs
 
 .. option:: -nopie, -no-pie
 
 .. option:: -noprebind
 
+.. option:: -noprofilelib
+
 .. option:: -noseglinkedit
 
 .. option:: -nostartfiles
 
 .. option:: -nostdinc, --no-standard-includes
 
 .. program:: clang1
 .. option:: -nostdinc++

clang/include/clang/Driver/Options.td

 def nocudalib : Flag<["-"], "nocudalib">;
 def nodefaultlibs : Flag<["-"], "nodefaultlibs">;
 def nofixprebinding : Flag<["-"], "nofixprebinding">;
 def nolibc : Flag<["-"], "nolibc">;
 def nomultidefs : Flag<["-"], "nomultidefs">;
 def nopie : Flag<["-"], "nopie">;
 def no_pie : Flag<["-"], "no-pie">, Alias<nopie>;
 def noprebind : Flag<["-"], "noprebind">;
+def noprofilelib : Flag<["-"], "noprofilelib">;
 def noseglinkedit : Flag<["-"], "noseglinkedit">;
 def nostartfiles : Flag<["-"], "nostartfiles">;
 def nostdinc : Flag<["-"], "nostdinc">, Flags<[CoreOption]>;
 def nostdlibinc : Flag<["-"], "nostdlibinc">;
 def nostdincxx : Flag<["-"], "nostdinc++">, Flags<[CC1Option]>,
   HelpText<"Disable standard #include directories for the C++ standard library">;
 def nostdlib : Flag<["-"], "nostdlib">;
 def nostdlibxx : Flag<["-"], "nostdlib++">;

clang/lib/Driver/ToolChain.cpp

 std::string ToolChain::getArchSpecificLibPath() const {
   SmallString<128> Path(getDriver().ResourceDir);
   llvm::sys::path::append(Path, "lib", getOSLibName(),
                           llvm::Triple::getArchTypeName(getArch()));
   return Path.str();
 }
 
 bool ToolChain::needsProfileRT(const ArgList &Args) {
+  if (Args.hasArg(options::OPT_noprofilelib))
+    return false;
+
   if (needsGCovInstrumentation(Args) ||
       Args.hasArg(options::OPT_fprofile_generate) ||
       Args.hasArg(options::OPT_fprofile_generate_EQ) ||
       Args.hasArg(options::OPT_fcs_profile_generate) ||
       Args.hasArg(options::OPT_fcs_profile_generate_EQ) ||
       Args.hasArg(options::OPT_fprofile_instr_generate) ||
       Args.hasArg(options::OPT_fprofile_instr_generate_EQ) ||
       Args.hasArg(options::OPT_fcreate_profile) ||

clang/test/Driver/noprofilelib.c

+// RUN: %clang -target i686-pc-linux-gnu -### %s 2>&1 \
+// RUN:     -fprofile-generate -noprofilelib | FileCheck %s
+// RUN: %clang -target i686-pc-linux-gnu -### %s 2>&1 \
+// RUN:     -fprofile-instr-generate -noprofilelib | FileCheck %s
+// CHECK-NOT: clang_rt.profile