From b94e1c934cbc78fd60a7f59d0545f894da69880c Mon Sep 17 00:00:00 2001
From: Jia Yuan Lo <jylo06g@gmail.com>
Date: Fri, 22 Jan 2021 00:01:20 +0800
Subject: [PATCH] Add C++ bitness test in SAH_SELECT_BITNESS

---
 m4/sah_select_bitness.m4 | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/m4/sah_select_bitness.m4 b/m4/sah_select_bitness.m4
index 78db13f7de..f238aa5187 100644
--- a/m4/sah_select_bitness.m4
+++ b/m4/sah_select_bitness.m4
@@ -59,6 +59,25 @@ AC_DEFUN([SAH_SELECT_BITNESS],[
     AC_MSG_RESULT([ok use $1])
   AC_LANG_POP([C])
 
+  AC_LANG_PUSH([C++])
+    AC_MSG_CHECKING([if C++ compiler can use -m$1])
+    if test "$1" != "${COMPILER_MODEL_BITS}"; then
+      echo "int main() { return 0; }" >conftest.$ac_ext
+      AC_REQUIRE_CPP
+      ${CXX} ${CXXFLAGS} ${CPPFLAGS} -m$1 -fno-lto -c conftest.$ac_ext 2>&AS_MESSAGE_LOG_FD >&AS_MESSAGE_LOG_FD
+      if test -f conftest.${OBJEXT}; then
+        if test -n "$(file conftest.${OBJEXT} | grep -i ${1}-bit)"; then
+          CXXFLAGS="${CXXFLAGS} -m$1"
+          AC_MSG_RESULT([ok use $1])
+        else
+          AC_MSG_ERROR([failed still $COMPILER_MODEL_BITS])
+        fi
+      fi
+      /bin/rm conftest.$ac_ext conftest.${OBJEXT}
+    fi
+    AC_MSG_RESULT([ok use $1])
+  AC_LANG_POP([C++])
+
   COMPILER_MODEL_BITS=$1
 ])