--- a/make/autoconf/flags-cflags.m4	Mon Sep 17 11:49:20 2018 +0200
+++ b/make/autoconf/flags-cflags.m4	Mon Sep 17 10:53:56 2018 +0200
@@ -373,6 +373,20 @@
 
   FLAGS_SETUP_CFLAGS_CPU_DEP([BUILD], [OPENJDK_BUILD_])
 
+  COMPILER_FP_CONTRACT_OFF_FLAG="-ffp-contract=off"
+  # Check that the compiler supports -ffp-contract=off flag
+  # Set FDLIBM_CFLAGS to -ffp-contract=off if it does. Empty
+  # otherwise.
+  # These flags are required for GCC-based builds of
+  # fdlibm with optimization without losing precision.
+  # Notably, -ffp-contract=off needs to be added for GCC >= 4.6.
+  if test "x$TOOLCHAIN_TYPE" = xgcc || test "x$TOOLCHAIN_TYPE" = xclang; then
+    FLAGS_COMPILER_CHECK_ARGUMENTS(ARGUMENT: [${COMPILER_FP_CONTRACT_OFF_FLAG}],
+	IF_TRUE: [FDLIBM_CFLAGS=${COMPILER_FP_CONTRACT_OFF_FLAG}],
+	IF_FALSE: [FDLIBM_CFLAGS=""])
+  fi
+  AC_SUBST(FDLIBM_CFLAGS)
+
   # Tests are only ever compiled for TARGET
   CFLAGS_TESTLIB="$CFLAGS_JDKLIB"
   CXXFLAGS_TESTLIB="$CXXFLAGS_JDKLIB"