commit 34ee5b9ce2d3ab1ccfb91016ee058949c69c1066

Author: Norvald H. Ryeng <norvald.ryeng@oracle.com>

Date:   Fri May 27 15:19:56 2016 +0200

    Bug#23046775 DIFFERENT FLOATING POINT RESULTS ON ARM64 AND POWERPC

    Backport from trunk.

    Problem: The -fexpensive-optimizations option to gcc causes ARM64 and

    PowerPC build to compute floating point operations slightly

    differently from other platforms. This flag is enabled by -O2 and

    higher optimization levels.

    Fix: Check for the unwanted floating point behavior in CMake and

    disable expensive-optimizations in GCC builds on platforms that

    experience this behavior.

diff --git a/cmake/build_configurations/compiler_options.cmake b/cmake/build_configurations/compiler_options.cmake

index 98d553a..f105c7a 100644

--- a/cmake/build_configurations/compiler_options.cmake

+++ b/cmake/build_configurations/compiler_options.cmake

@@ -15,6 +15,7 @@

 INCLUDE(CheckCCompilerFlag)

 INCLUDE(CheckCXXCompilerFlag)

+INCLUDE(cmake/floating_point.cmake)

 IF(SIZEOF_VOIDP EQUAL 4)

   SET(32BIT 1)

@@ -33,6 +34,10 @@ IF(UNIX)

     IF(WITH_VALGRIND)

       SET(COMMON_C_FLAGS             "-fno-inline ${COMMON_C_FLAGS}")

     ENDIF()

+    # Disable optimizations that change floating point results

+    IF(HAVE_C_FLOATING_POINT_OPTIMIZATION_PROBLEMS)

+      SET(COMMON_C_FLAGS "${COMMON_C_FLAGS} -fno-expensive-optimizations")

+    ENDIF()

     SET(CMAKE_C_FLAGS_DEBUG          "${COMMON_C_FLAGS}")

     SET(CMAKE_C_FLAGS_RELWITHDEBINFO "-O3 ${COMMON_C_FLAGS}")

   ENDIF()

@@ -48,6 +53,10 @@ IF(UNIX)

     IF(WITH_VALGRIND)

       SET(COMMON_CXX_FLAGS             "-fno-inline ${COMMON_CXX_FLAGS}")

     ENDIF()

+    # Disable optimizations that change floating point results

+    IF(HAVE_CXX_FLOATING_POINT_OPTIMIZATION_PROBLEMS)

+      SET(COMMON_CXX_FLAGS "${COMMON_CXX_FLAGS} -fno-expensive-optimizations")

+    ENDIF()

     SET(CMAKE_CXX_FLAGS_DEBUG          "${COMMON_CXX_FLAGS}")

     SET(CMAKE_CXX_FLAGS_RELWITHDEBINFO "-O3 ${COMMON_CXX_FLAGS}")

   ENDIF()

diff --git a/cmake/floating_point.cmake b/cmake/floating_point.cmake

new file mode 100644

index 0000000..6db63ad

--- /dev/null

+++ b/cmake/floating_point.cmake

@@ -0,0 +1,56 @@

+# Copyright (c) 2016, Oracle and/or its affiliates. All rights reserved.

+#

+# This program is free software; you can redistribute it and/or modify

+# it under the terms of the GNU General Public License as published by

+# the Free Software Foundation; version 2 of the License.

+#

+# This program is distributed in the hope that it will be useful,

+# but WITHOUT ANY WARRANTY; without even the implied warranty of

+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

+# GNU General Public License for more details.

+#

+# You should have received a copy of the GNU General Public License

+# along with this program; if not, write to the Free Software

+# Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA

+

+INCLUDE(CheckCSourceRuns)

+INCLUDE(CheckCXXSourceRuns)

+

+SET(code "

+  int main (int argc, char **argv)

+  {

+    double n[21] = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,

+                     0, 0, 0, 1, 1, 1, 1, 1, 1, 1,1 };

+    double m= 0, s= 0;

+    int i;

+    for(i= 0; i < 21; i++)

+    {

+      double m_kminusone= m;

+      m= m_kminusone + (n[i] - m_kminusone) / (double) (i + 2);

+      s= s + (n[i] - m_kminusone) * (n[i] - m);

+    }

+    /*

+      s should now be either 5e 74 d1 45 17 5d 14 40 or

+      40 14 5d 17 45 d1 74 5e, depending on endianness. If the floating point

+      operations are over optimized, the least significant byte is 5d instead

+      of 5e.

+    */

+    return (*(unsigned char*)(&s) == 0x5e ||

+            *((unsigned char*)(&s) + 7) == 0x5e);

+  }"

+)

+

+SET(SAVE_CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS}")

+SET(CMAKE_REQUIRED_FLAGS

+  "${CMAKE_REQUIRED_FLAGS} -O3 -fexpensive-optimizations"

+)

+

+IF(CMAKE_COMPILER_IS_GNUCC)

+  CHECK_C_SOURCE_RUNS("${code}" HAVE_C_FLOATING_POINT_OPTIMIZATION_PROBLEMS)

+ENDIF()

+

+IF(CMAKE_COMPILER_IS_GNUCXX)

+  CHECK_CXX_SOURCE_RUNS("${code}" HAVE_CXX_FLOATING_POINT_OPTIMIZATION_PROBLEMS)

+ENDIF()

+

+SET(CMAKE_REQUIRED_FLAGS "${SAVE_CMAKE_REQUIRED_FLAGS}")