[lit][tests]Add libc++ to link XRay test cases if libc++ is used to build CLANG

[xingxue]

Summary

When libc++ is used to build CLANG, its XRay libraries libclang_rt.xray-*.a have dependencies on libc++. Therefore, libc++ is needed to link and run XRay test cases. For Linux -rpath is also needed to specify where to load libc++. This change sets macro LLVM_LIBCXX_USED to 1 if libc++ is actually used in the build. XRay tests then check the flag and add -L<llvm_shlib_dir> -lc++ and -Wl,-rpath=<llvm_shlib_dir> if needed.

[hubert.reinterpretcast]

The test updates make sense given the current Clang driver behaviour; however, I think there is a question as to whether the Clang driver should be updated to add -lc++, etc. as necessary when it "automatically" links in compiler-rt libraries with such dependencies.

[hubert.reinterpretcast]

In D61016#1476442, @hubert.reinterpretcast wrote:

The test updates make sense given the current Clang driver behaviour; however, I think there is a question as to whether the Clang driver should be updated to add -lc++, etc. as necessary when it "automatically" links in compiler-rt libraries with such dependencies.

Thanks @xingxue for the off-list discussion. I agree that the Clang driver behaviour is a larger design question over packaging that should be a separate discussion at a later time. I'm good with this change to the tests, but I'd like to see if the other reviewers have comments to add.

[dberris]

LGTM -- thanks for looking into this!

[hubert.reinterpretcast]

@xingxue, I believe that you have had a good number of patches committed into the project already (rCXX195144, rL356104, rCRT356844). Please go ahead with requesting commit access, and commit this patch when you are ready.

[xingxue]

@hubert.reinterpretcast, @dberris, thanks for the review! I will commit once I get the permission.

[amyk]

I think this LGTM.

compiler-rt/trunk/test/lit.common.configured.in

 config.available_features.add('target-is-%s' % config.target_arch)
 
 if config.enable_per_target_runtime_dir:
   set_default("target_suffix", "")
 else:
   set_default("target_suffix", "-%s" % config.target_arch)
 
 set_default("have_zlib", "@HAVE_LIBZ@")
+set_default("libcxx_used", "@LLVM_LIBCXX_USED@")
 
 # LLVM tools dir can be passed in lit parameters, so try to
 # apply substitution.
 try:
   config.llvm_tools_dir = config.llvm_tools_dir % lit_config.params
   config.clang = config.clang % lit_config.params
   config.compiler_rt_libdir = config.compiler_rt_libdir % lit_config.params
 except KeyError as e:
   key, = e.args
   lit_config.fatal("unable to find %r parameter, use '--param=%s=VALUE'" % (key, key))
 
 if not os.path.exists(config.clang):
   lit_config.fatal("Can't find compiler on path %r" % config.clang)
 
 # Setup attributes common for all compiler-rt projects.
 lit_config.load_config(config, "@COMPILER_RT_SOURCE_DIR@/test/lit.common.cfg")

compiler-rt/trunk/test/xray/lit.cfg

 # -*- Python -*-
 
 import os
 
 # Setup config name.
 config.name = 'XRay' + config.name_suffix
 
 # Setup source root.
 config.test_source_root = os.path.dirname(__file__)
 
 # Setup default compiler flags use with -fxray-instrument option.
 clang_xray_cflags = (['-fxray-instrument', config.target_cflags])
-clang_xray_cxxflags = config.cxx_mode_flags + clang_xray_cflags
 
+# If libc++ was used to build XRAY libraries, libc++ is needed. Fix applied
+# to Linux only since -rpath may not be portable. This can be extended to
+# other platforms.
+if config.libcxx_used == "1" and config.host_os == "Linux":
+  clang_xray_cflags = clang_xray_cflags + (['-L%s -lc++ -Wl,-rpath=%s'
+                                          % (config.llvm_shlib_dir,
+                                             config.llvm_shlib_dir)])
+
+clang_xray_cxxflags = config.cxx_mode_flags + clang_xray_cflags
 
 def build_invocation(compile_flags):
   return ' ' + ' '.join([config.clang] + compile_flags) + ' '
 
 # Assume that llvm-xray is in the config.llvm_tools_dir.
 llvm_xray = os.path.join(config.llvm_tools_dir, 'llvm-xray')
 
 # Setup substitutions.

llvm/trunk/cmake/modules/HandleLLVMStdlib.cmake

 # This CMake module is responsible for setting the standard library to libc++
 # if the user has requested it.
 
 include(DetermineGCCCompatible)
 
 if(NOT DEFINED LLVM_STDLIB_HANDLED)
   set(LLVM_STDLIB_HANDLED ON)
 
   function(append value)
     foreach(variable ${ARGN})
       set(${variable} "${${variable}} ${value}" PARENT_SCOPE)
     endforeach(variable)
   endfunction()
 
   include(CheckCXXCompilerFlag)
   include(CheckLinkerFlag)
+  set(LLVM_LIBCXX_USED 0)
   if(LLVM_ENABLE_LIBCXX)
     if(LLVM_COMPILER_IS_GCC_COMPATIBLE)
       check_cxx_compiler_flag("-stdlib=libc++" CXX_COMPILER_SUPPORTS_STDLIB)
       check_linker_flag("-stdlib=libc++" CXX_LINKER_SUPPORTS_STDLIB)
       if(CXX_COMPILER_SUPPORTS_STDLIB AND CXX_LINKER_SUPPORTS_STDLIB)
         append("-stdlib=libc++"
           CMAKE_CXX_FLAGS CMAKE_EXE_LINKER_FLAGS CMAKE_SHARED_LINKER_FLAGS
           CMAKE_MODULE_LINKER_FLAGS)
+        set(LLVM_LIBCXX_USED 1)
       else()
         message(WARNING "Can't specify libc++ with '-stdlib='")
       endif()
     else()
       message(WARNING "Not sure how to specify libc++ for this compiler")
     endif()
   endif()
 endif()