+dnl Check both GCC and Clang for sufficiently modern versions. These checks can
+dnl be bypassed by passing a flag if necessary on a platform. We have to do
+dnl these checks here so that we have the configuration of the standard C++
+dnl library finished.
+AC_ARG_ENABLE(compiler-version-checks,
+ AS_HELP_STRING([--enable-compiler-version-checks],
+ [Check the version of the host compiler (default is YES)]),,
+ enableval=default)
+case "$enableval" in
+ no)
+ ;;
+ yes|default)
+ AC_LANG_PUSH([C++])
+ case "$llvm_cv_cxx_compiler" in
+ clang)
+ AC_MSG_CHECKING([whether Clang is new enough])
+ AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
+#if __clang_major__ < 3 || (__clang_major__ == 3 && __clang_minor__ < 1)
+#error This version of Clang is too old to build LLVM
+#endif
+]])],
+ [AC_MSG_RESULT([yes])],
+ [AC_MSG_RESULT([no])
+ AC_MSG_ERROR([
+The selected Clang compiler is not new enough to build LLVM. Please upgrade to
+Clang 3.1. You may pass --disable-compiler-version-checks to configure to
+bypass these sanity checks.])])
+
+ dnl Note that libstdc++4.6 is known broken for C++11 builds. The errors
+ dnl are sometimes deeply confusing though. Here we test for an obvious
+ dnl incomplete feature in 4.6's standard library that was completed in
+ dnl 4.7's. We also have to disable this test if 'ENABLE_LIBCPP' is set
+ dnl because the enable flags don't actually fix CXXFLAGS, they rely on
+ dnl that happening in the Makefile.
+ if test "$ENABLE_LIBCPP" -eq 0 ; then
+ AC_MSG_CHECKING([whether Clang will select a modern C++ standard library])
+ llvm_cv_old_cxxflags="$CXXFLAGS"
+ CXXFLAGS="$CXXFLAGS -std=c++0x"
+ AC_LINK_IFELSE([AC_LANG_SOURCE([[
+#include <atomic>
+std::atomic<float> x(0.0f);
+int main() { return (float)x; }
+]])],
+ [AC_MSG_RESULT([yes])],
+ [AC_MSG_RESULT([no])
+ AC_MSG_ERROR([
+We detected a missing feature in the standard C++ library that was known to be
+missing in libstdc++4.6 and implemented in libstdc++4.7. There are numerous
+C++11 problems with 4.6's library, and we don't support GCCs or libstdc++ older
+than 4.7. You will need to update your system and ensure Clang uses the newer
+standard library.
+
+If this error is incorrect or you need to force things to work, you may pass
+'--disable-compiler-version-checks' to configure to bypass this test.])])
+ CXXFLAGS="$llvm_cv_old_cxxflags"
+ fi
+ ;;
+ gcc)
+ AC_MSG_CHECKING([whether GCC is new enough])
+ AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
+#if __GNUC__ < 4 || (__GNUC__ == 4 && __GNUC_MINOR__ < 7)
+#error This version of GCC is too old to build LLVM
+#endif
+]])],
+ [AC_MSG_RESULT([yes])],
+ [AC_MSG_RESULT([no])
+ AC_MSG_ERROR([
+The selected GCC C++ compiler is not new enough to build LLVM. Please upgrade
+to GCC 4.7. You may pass --disable-compiler-version-checks to configure to
+bypass these sanity checks.])])
+ ;;
+ unknown)
+ ;;
+ esac
+ AC_LANG_POP([C++])
+ ;;
+ *)
+ AC_MSG_ERROR([Invalid setting for --enable-compiler-version-checks. Use "yes" or "no"])
+ ;;
+esac
+
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