[CMake] Support builtins as Clang default rtlib in compiler-rt

Use compiler-rt builtins when selected as default Clang rtlib and avoid
explicitly passing -rtlib= flag to avoid the "argument unused during
compilation" warning.

This is a partial alternative to D47094 that does not rely on compiler
runtime checks.

Differential Revision: https://reviews.llvm.org/D47115

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@333037 91177308-0d34-0410-b5e6-96231b3b80d8

Author: petrhosek

CMakeLists.txt

@@ -152,9 +152,19 @@ else()
   set(SANITIZER_CXX_ABI_SYSTEM 1)
 endif()
 
-option(SANITIZER_USE_COMPILER_RT "Use compiler-rt builtins instead of libgcc" OFF)
+set(COMPILER_RT_RUNTIME "default" CACHE STRING
+    "Compiler runtime to use.")
+
+if (COMPILER_RT_RUNTIME STREQUAL "default")
+  if (CLANG_DEFAULT_RTLIB STREQUAL "compiler-rt")
+    set(COMPILER_RT_RUNTIME_LIBRARY "builtins")
+  elseif (FUCHSIA)
+    set(COMPILER_RT_RUNTIME_LIBRARY "builtins")
+  endif()
+else()
+  set(COMPILER_RT_RUNTIME_LIBRARY "${COMPILER_RT_RUNTIME}")
+endif()
 
-include(HandleCompilerRT)
 include(config-ix)
 
 #================================
@@ -303,9 +313,7 @@ append_list_if(COMPILER_RT_HAS_WD4800_FLAG /wd4800 SANITIZER_COMMON_CFLAGS)
 # Set common link flags.
 append_list_if(COMPILER_RT_HAS_NODEFAULTLIBS_FLAG -nodefaultlibs SANITIZER_COMMON_LINK_FLAGS)
 
-if (SANITIZER_USE_COMPILER_RT)
-  list(APPEND SANITIZER_COMMON_LINK_FLAGS -rtlib=compiler-rt)
-  find_compiler_rt_library(builtins COMPILER_RT_BUILTINS_LIBRARY)
+if (COMPILER_RT_RUNTIME_LIBRARY STREQUAL "builtins")
   list(APPEND SANITIZER_COMMON_LINK_LIBS ${COMPILER_RT_BUILTINS_LIBRARY})
 else()
   if (ANDROID)

cmake/config-ix.cmake

@@ -13,7 +13,10 @@ function(check_linker_flag flag out_var)
 endfunction()
 
 check_library_exists(c fopen "" COMPILER_RT_HAS_LIBC)
-if (NOT SANITIZER_USE_COMPILER_RT)
+if (COMPILER_RT_RUNTIME_LIBRARY STREQUAL "builtins")
+  include(HandleCompilerRT)
+  find_compiler_rt_library(builtins COMPILER_RT_BUILTINS_LIBRARY)
+else()
   if (ANDROID)
     check_library_exists(gcc __gcc_personality_v0 "" COMPILER_RT_HAS_GCC_LIB)
   else()
@@ -27,9 +30,7 @@ if (COMPILER_RT_HAS_NODEFAULTLIBS_FLAG)
   if (COMPILER_RT_HAS_LIBC)
     list(APPEND CMAKE_REQUIRED_LIBRARIES c)
   endif ()
-  if (SANITIZER_USE_COMPILER_RT)
-    list(APPEND CMAKE_REQUIRED_FLAGS -rtlib=compiler-rt)
-    find_compiler_rt_library(builtins COMPILER_RT_BUILTINS_LIBRARY)
+  if (COMPILER_RT_RUNTIME_LIBRARY STREQUAL "builtins")
     list(APPEND CMAKE_REQUIRED_LIBRARIES "${COMPILER_RT_BUILTINS_LIBRARY}")
   elseif (COMPILER_RT_HAS_GCC_S_LIB)
     list(APPEND CMAKE_REQUIRED_LIBRARIES gcc_s)