Index: llvm/trunk/CMakeLists.txt
===================================================================
--- llvm/trunk/CMakeLists.txt
+++ llvm/trunk/CMakeLists.txt
@@ -421,13 +421,21 @@
   option(LLVM_ENABLE_MODULE_DEBUGGING "Compile with -gmodules." OFF)
   option(LLVM_ENABLE_LOCAL_SUBMODULE_VISIBILITY "Compile with -fmodules-local-submodule-visibility." ON)
 endif()
-option(LLVM_ENABLE_CXX1Y "Compile with C++1y enabled." OFF)
-option(LLVM_ENABLE_CXX1Z "Compile with C++1z enabled." OFF)
 option(LLVM_ENABLE_LIBCXX "Use libc++ if available." OFF)
 option(LLVM_ENABLE_LLD "Use lld as C and C++ linker." OFF)
 option(LLVM_ENABLE_PEDANTIC "Compile with pedantic enabled." ON)
 option(LLVM_ENABLE_WERROR "Fail and stop if a warning is triggered." OFF)
 
+set(LLVM_CXX_STD_default "c++11")
+# Preserve behaviour of legacy cache variables
+if (LLVM_ENABLE_CXX1Y)
+  set(LLVM_CXX_STD_default "c++1y")
+elseif (LLVM_ENABLE_CXX1Z)
+  set(LLVM_CXX_STD_default "c++1z")
+endif()
+set(LLVM_CXX_STD ${LLVM_CXX_STD_default}
+    CACHE STRING "C++ standard to use for compilation.")
+
 option(LLVM_ENABLE_DUMP "Enable dump functions even when assertions are disabled" OFF)
 
 if( NOT uppercase_CMAKE_BUILD_TYPE STREQUAL "DEBUG" )
Index: llvm/trunk/cmake/modules/HandleLLVMOptions.cmake
===================================================================
--- llvm/trunk/cmake/modules/HandleLLVMOptions.cmake
+++ llvm/trunk/cmake/modules/HandleLLVMOptions.cmake
@@ -437,25 +437,18 @@
   append_if(LLVM_ENABLE_WERROR "-Wno-error" CMAKE_REQUIRED_FLAGS)
   add_flag_if_supported("-Werror=date-time" WERROR_DATE_TIME)
   add_flag_if_supported("-Werror=unguarded-availability-new" WERROR_UNGUARDED_AVAILABILITY_NEW)
-  if (LLVM_ENABLE_CXX1Y)
-    check_cxx_compiler_flag("-std=c++1y" CXX_SUPPORTS_CXX1Y)
-    append_if(CXX_SUPPORTS_CXX1Y "-std=c++1y" CMAKE_CXX_FLAGS)
-  elseif(LLVM_ENABLE_CXX1Z)
-    check_cxx_compiler_flag("-std=c++1z" CXX_SUPPORTS_CXX1Z)
-    append_if(CXX_SUPPORTS_CXX1Z "-std=c++1z" CMAKE_CXX_FLAGS)
-  else()
-    check_cxx_compiler_flag("-std=c++11" CXX_SUPPORTS_CXX11)
-    if (CXX_SUPPORTS_CXX11)
-      if (CYGWIN OR MINGW)
-        # MinGW and Cygwin are a bit stricter and lack things like
-        # 'strdup', 'stricmp', etc in c++11 mode.
-        append("-std=gnu++11" CMAKE_CXX_FLAGS)
-      else()
-        append("-std=c++11" CMAKE_CXX_FLAGS)
-      endif()
+  check_cxx_compiler_flag("-std=${LLVM_CXX_STD}" CXX_SUPPORTS_CXX_STD)
+  if (CXX_SUPPORTS_CXX_STD)
+   if (CYGWIN OR MINGW)
+      # MinGW and Cygwin are a bit stricter and lack things like
+      # 'strdup', 'stricmp', etc in c++11 mode.
+      string(REPLACE "c++" "gnu++" "${LLVM_CXX_STD}" gnu_LLVM_CXX_STD)
+      append("-std=${gnu_LLVM_CXX_STD}" CMAKE_CXX_FLAGS)
     else()
-      message(FATAL_ERROR "LLVM requires C++11 support but the '-std=c++11' flag isn't supported.")
+      append("-std=${LLVM_CXX_STD}" CMAKE_CXX_FLAGS)
     endif()
+  else()
+    message(FATAL_ERROR "The host compiler does not support '-std=${LLVM_CXX_STD}'.")
   endif()
   if (LLVM_ENABLE_MODULES)
     set(OLD_CMAKE_REQUIRED_FLAGS ${CMAKE_REQUIRED_FLAGS})
Index: llvm/trunk/docs/CMake.rst
===================================================================
--- llvm/trunk/docs/CMake.rst
+++ llvm/trunk/docs/CMake.rst
@@ -266,8 +266,8 @@
 **LLVM_ENABLE_THREADS**:BOOL
   Build with threads support, if available. Defaults to ON.
 
-**LLVM_ENABLE_CXX1Y**:BOOL
-  Build in C++1y mode, if available. Defaults to OFF.
+**LLVM_CXX_STD**:STRING
+  Build with the specified C++ standard. Defaults to "c++11".
 
 **LLVM_ENABLE_ASSERTIONS**:BOOL
   Enables code assertions. Defaults to ON if and only if ``CMAKE_BUILD_TYPE``