diff --git a/compiler-rt/CMakeLists.txt b/compiler-rt/CMakeLists.txt
--- a/compiler-rt/CMakeLists.txt
+++ b/compiler-rt/CMakeLists.txt
@@ -621,32 +621,6 @@
 
 option(COMPILER_RT_USE_LIBCXX
   "Enable compiler-rt to use libc++ from the source tree" ON)
-if(COMPILER_RT_USE_LIBCXX)
-  if(LLVM_ENABLE_PROJECTS_USED)
-    # Don't use libcxx if LLVM_ENABLE_PROJECTS does not enable it.
-    set(COMPILER_RT_LIBCXX_PATH ${LLVM_EXTERNAL_LIBCXX_SOURCE_DIR})
-    set(COMPILER_RT_LIBCXXABI_PATH ${LLVM_EXTERNAL_LIBCXXABI_SOURCE_DIR})
-  else()
-    foreach(path IN ITEMS ${LLVM_MAIN_SRC_DIR}/projects/libcxx
-                          ${LLVM_MAIN_SRC_DIR}/runtimes/libcxx
-                          ${LLVM_MAIN_SRC_DIR}/../libcxx
-                          ${LLVM_EXTERNAL_LIBCXX_SOURCE_DIR})
-      if(IS_DIRECTORY ${path})
-        set(COMPILER_RT_LIBCXX_PATH ${path})
-        break()
-      endif()
-    endforeach()
-    foreach(path IN ITEMS ${LLVM_MAIN_SRC_DIR}/projects/libcxxabi
-                          ${LLVM_MAIN_SRC_DIR}/runtimes/libcxxabi
-                          ${LLVM_MAIN_SRC_DIR}/../libcxxabi
-                          ${LLVM_EXTERNAL_LIBCXXABI_SOURCE_DIR})
-      if(IS_DIRECTORY ${path})
-        set(COMPILER_RT_LIBCXXABI_PATH ${path})
-        break()
-      endif()
-    endforeach()
-  endif()
-endif()
 
 set(COMPILER_RT_LLD_PATH ${LLVM_MAIN_SRC_DIR}/tools/lld)
 if(EXISTS ${COMPILER_RT_LLD_PATH}/ AND LLVM_TOOL_LLD_BUILD)
diff --git a/compiler-rt/cmake/Modules/AddCompilerRT.cmake b/compiler-rt/cmake/Modules/AddCompilerRT.cmake
--- a/compiler-rt/cmake/Modules/AddCompilerRT.cmake
+++ b/compiler-rt/cmake/Modules/AddCompilerRT.cmake
@@ -585,13 +585,6 @@
 #                   CFLAGS <list of compile flags>
 #                   USE_TOOLCHAIN)
 macro(add_custom_libcxx name prefix)
-  if(NOT COMPILER_RT_LIBCXX_PATH)
-    message(FATAL_ERROR "libcxx not found!")
-  endif()
-  if(NOT COMPILER_RT_LIBCXXABI_PATH)
-    message(FATAL_ERROR "libcxxabi not found!")
-  endif()
-
   cmake_parse_arguments(LIBCXX "USE_TOOLCHAIN" "" "DEPS;CFLAGS;CMAKE_ARGS" ${ARGN})
 
   if(LIBCXX_USE_TOOLCHAIN)
diff --git a/compiler-rt/lib/fuzzer/CMakeLists.txt b/compiler-rt/lib/fuzzer/CMakeLists.txt
--- a/compiler-rt/lib/fuzzer/CMakeLists.txt
+++ b/compiler-rt/lib/fuzzer/CMakeLists.txt
@@ -59,9 +59,7 @@
 
 set(LIBFUZZER_CFLAGS ${COMPILER_RT_COMMON_CFLAGS})
 
-if(OS_NAME MATCHES "Linux|Fuchsia" AND
-   COMPILER_RT_LIBCXX_PATH AND
-   COMPILER_RT_LIBCXXABI_PATH)
+if(OS_NAME MATCHES "Linux|Fuchsia" AND COMPILER_RT_USE_LIBCXX)
   list(APPEND LIBFUZZER_CFLAGS -D_LIBCPP_ABI_VERSION=Fuzzer)
   append_list_if(COMPILER_RT_HAS_NOSTDINCXX_FLAG -nostdinc++ LIBFUZZER_CFLAGS)
 elseif(TARGET cxx-headers OR HAVE_LIBCXX)
@@ -134,9 +132,7 @@
   CFLAGS ${LIBFUZZER_CFLAGS}
   PARENT_TARGET fuzzer)
 
-if(OS_NAME MATCHES "Linux|Fuchsia" AND
-   COMPILER_RT_LIBCXX_PATH AND
-   COMPILER_RT_LIBCXXABI_PATH)
+if(OS_NAME MATCHES "Linux|Fuchsia" AND COMPILER_RT_USE_LIBCXX)
   macro(partially_link_libcxx name dir arch)
     get_target_flags_for_arch(${arch} target_cflags)
     if(CMAKE_CXX_COMPILER_ID MATCHES Clang)
diff --git a/compiler-rt/lib/fuzzer/tests/CMakeLists.txt b/compiler-rt/lib/fuzzer/tests/CMakeLists.txt
--- a/compiler-rt/lib/fuzzer/tests/CMakeLists.txt
+++ b/compiler-rt/lib/fuzzer/tests/CMakeLists.txt
@@ -30,9 +30,7 @@
   list(APPEND LIBFUZZER_UNITTEST_LINK_FLAGS -lpthread)
 endif()
 
-if(CMAKE_SYSTEM_NAME STREQUAL "Linux" AND
-   COMPILER_RT_LIBCXX_PATH AND
-   COMPILER_RT_LIBCXXABI_PATH)
+if(CMAKE_SYSTEM_NAME STREQUAL "Linux" AND COMPILER_RT_USE_LIBCXX)
   list(APPEND LIBFUZZER_UNITTEST_CFLAGS -nostdinc++ -fno-exceptions)
   list(APPEND LIBFUZZER_UNITTEST_LINK_FLAGS -nostdlib++ -fno-exceptions)
 endif()
@@ -60,9 +58,7 @@
     ARCHIVE_OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
     FOLDER "Compiler-RT Runtime tests")
 
-  if(CMAKE_SYSTEM_NAME STREQUAL "Linux" AND
-     COMPILER_RT_LIBCXX_PATH AND
-     COMPILER_RT_LIBCXXABI_PATH)
+  if(CMAKE_SYSTEM_NAME STREQUAL "Linux" AND COMPILER_RT_USE_LIBCXX)
     file(GLOB libfuzzer_headers ../*.h)
     set(LIBFUZZER_TEST_RUNTIME_DEPS libcxx_fuzzer_${arch}-build ${libfuzzer_headers})
     set(LIBFUZZER_TEST_RUNTIME_CFLAGS -isystem ${LIBCXX_${arch}_PREFIX}/include/c++/v1)
diff --git a/compiler-rt/lib/msan/tests/CMakeLists.txt b/compiler-rt/lib/msan/tests/CMakeLists.txt
--- a/compiler-rt/lib/msan/tests/CMakeLists.txt
+++ b/compiler-rt/lib/msan/tests/CMakeLists.txt
@@ -130,9 +130,7 @@
 endmacro()
 
 # We should only build MSan unit tests if we can build instrumented libcxx.
-if(COMPILER_RT_CAN_EXECUTE_TESTS AND
-   COMPILER_RT_LIBCXX_PATH AND
-   COMPILER_RT_LIBCXXABI_PATH)
+if(COMPILER_RT_CAN_EXECUTE_TESTS AND COMPILER_RT_USE_LIBCXX)
   foreach(arch ${MSAN_SUPPORTED_ARCH})
     get_target_flags_for_arch(${arch} TARGET_CFLAGS)
     set(LIBCXX_PREFIX ${CMAKE_CURRENT_BINARY_DIR}/../libcxx_msan_${arch})
diff --git a/compiler-rt/lib/tsan/CMakeLists.txt b/compiler-rt/lib/tsan/CMakeLists.txt
--- a/compiler-rt/lib/tsan/CMakeLists.txt
+++ b/compiler-rt/lib/tsan/CMakeLists.txt
@@ -24,8 +24,7 @@
 endif()
 
 # Build libcxx instrumented with TSan.
-if(COMPILER_RT_LIBCXX_PATH AND
-   COMPILER_RT_LIBCXXABI_PATH AND
+if(COMPILER_RT_USE_LIBCXX AND
    COMPILER_RT_TEST_COMPILER_ID STREQUAL "Clang" AND
    NOT ANDROID)
   set(libcxx_tsan_deps)
diff --git a/compiler-rt/test/msan/CMakeLists.txt b/compiler-rt/test/msan/CMakeLists.txt
--- a/compiler-rt/test/msan/CMakeLists.txt
+++ b/compiler-rt/test/msan/CMakeLists.txt
@@ -45,9 +45,7 @@
   list(APPEND MSAN_TEST_DEPS msan)
 endif()
 
-if(COMPILER_RT_INCLUDE_TESTS AND
-   COMPILER_RT_LIBCXX_PATH AND
-   COMPILER_RT_LIBCXXABI_PATH)
+if(COMPILER_RT_INCLUDE_TESTS AND COMPILER_RT_USE_LIBCXX)
   configure_lit_site_cfg(
     ${CMAKE_CURRENT_SOURCE_DIR}/Unit/lit.site.cfg.py.in
     ${CMAKE_CURRENT_BINARY_DIR}/Unit/lit.site.cfg.py)
diff --git a/compiler-rt/test/tsan/CMakeLists.txt b/compiler-rt/test/tsan/CMakeLists.txt
--- a/compiler-rt/test/tsan/CMakeLists.txt
+++ b/compiler-rt/test/tsan/CMakeLists.txt
@@ -7,8 +7,7 @@
 if(NOT COMPILER_RT_STANDALONE_BUILD)
   list(APPEND TSAN_TEST_DEPS tsan)
 endif()
-if(COMPILER_RT_LIBCXX_PATH AND
-   COMPILER_RT_LIBCXXABI_PATH AND
+if(COMPILER_RT_USE_LIBCXX AND
    COMPILER_RT_TEST_COMPILER_ID STREQUAL "Clang"
    AND NOT APPLE AND NOT ANDROID)
   list(APPEND TSAN_TEST_DEPS libcxx_tsan)