Only use LTO when compiling Ceres itself, not tests or examples.

- If Ceres is built as a shared library, and LTO is enabled for Ceres
  and the tests, then type_info::operator==() incorrectly returns false
  in gtests' CheckedDowncastToActualType() in the following tests:
-- levenberg_marquardt_strategy_test.
-- gradient_checking_cost_function_test.
  on at least Xcode 6 & 7 as reported here:
  https://github.com/google/googletest/issues/595.
- This does not appear to be a gtest issue, but is perhaps an LLVM bug
  or an RTTI shared library issue.  Either way, disabling the use of
  LTO when compiling the test application resolves the issue.
- Allow LTO to be enabled for GCC, if it is supported.
- Add CMake function to allow easy appending to target properties s/t
  Ceres library-specific compile flags can be iteratively constructed.

Change-Id: I923e6aae4f7cefa098cf32b2f8fc19389e7918c9

CMakeLists.txt

@@ -558,19 +558,6 @@ if (CMAKE_BUILD_TYPE STREQUAL "Release")
       endif (GCC_VERSION VERSION_LESS 4.3)
     endif (CMAKE_SYSTEM_NAME MATCHES "Darwin")
   endif (CMAKE_COMPILER_IS_GNUCXX)
-  if (CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
-    # Use of -flto requires use of gold linker & LLVM-gold plugin, which might
-    # well not be present / in use and without which files will compile, but
-    # not link ('file not recognized') so explicitly check for support
-    include(CheckCXXCompilerFlag)
-    check_cxx_compiler_flag("-flto" HAVE_LTO_SUPPORT)
-    if (HAVE_LTO_SUPPORT)
-      message(STATUS "Enabling link-time optimization (-flto)")
-      set(CERES_CXX_FLAGS "${CERES_CXX_FLAGS} -flto")
-    else ()
-      message(STATUS "Compiler/linker does not support link-time optimization (-flto), disabling.")
-    endif (HAVE_LTO_SUPPORT)
-  endif ()
 endif (CMAKE_BUILD_TYPE STREQUAL "Release")
 
 set (CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE} ${CERES_CXX_FLAGS}")

cmake/AppendTargetProperty.cmake

@@ -0,0 +1,61 @@
+# Ceres Solver - A fast non-linear least squares minimizer
+# Copyright 2015 Google Inc. All rights reserved.
+# http://ceres-solver.org/
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are met:
+#
+# * Redistributions of source code must retain the above copyright notice,
+#   this list of conditions and the following disclaimer.
+# * Redistributions in binary form must reproduce the above copyright notice,
+#   this list of conditions and the following disclaimer in the documentation
+#   and/or other materials provided with the distribution.
+# * Neither the name of Google Inc. nor the names of its contributors may be
+#   used to endorse or promote products derived from this software without
+#   specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+# ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+# LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+# CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+# SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+# INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+# CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+# ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+# POSSIBILITY OF SUCH DAMAGE.
+#
+# Author: alexs.mac@gmail.com (Alex Stewart)
+
+# Append item(s) to a property on a declared CMake target:
+#
+#    append_target_property(target property item_to_append1
+#                                           [... item_to_appendN])
+#
+# The set_target_properties() CMake function will overwrite the contents of the
+# specified target property.  This function instead appends to it, so can
+# be called multiple times with the same target & property to iteratively
+# populate it.
+function(append_target_property TARGET PROPERTY)
+  if (NOT TARGET ${TARGET})
+    message(FATAL_ERROR "Invalid target: ${TARGET} cannot append: ${ARGN} "
+      "to property: ${PROPERTY}")
+  endif()
+  if (NOT PROPERTY)
+    message(FATAL_ERROR "Invalid property to update for target: ${TARGET}")
+  endif()
+  # Get the initial state of the specified property for the target s/t
+  # we can append to it (not overwrite it).
+  get_target_property(INITIAL_PROPERTY_STATE ${TARGET} ${PROPERTY})
+  if (NOT INITIAL_PROPERTY_STATE)
+    # Ensure that if the state is unset, we do not insert the XXX-NOTFOUND
+    # returned by CMake into the property.
+    set(INITIAL_PROPERTY_STATE "")
+  endif()
+  # Delistify (remove ; separators) the potentially set of items to append
+  # to the specified target property.
+  string(REPLACE ";" " " ITEMS_TO_APPEND "${ARGN}")
+  set_target_properties(${TARGET} PROPERTIES ${PROPERTY}
+    "${INITIAL_PROPERTY_STATE} ${ITEMS_TO_APPEND}")
+endfunction()

docs/source/version_history.rst

@@ -27,6 +27,8 @@ New Features
 
 Bug Fixes & Minor Changes
 -------------------------
+#. Use link-time optimisation (LTO) only when compiling Ceres itself,
+   not tests or examples, to bypass gtest / type_info::operator== issue.
 #. Use old minimum iOS version flags on Xcode < 7.0.
 #. Add gtest-specific flags when building/using as a shared library.
 #. Clean up iOS.cmake to use xcrun/xcodebuild & libtool.

internal/ceres/CMakeLists.txt

@@ -184,6 +184,7 @@ set_target_properties(ceres PROPERTIES
   VERSION ${CERES_VERSION}
   SOVERSION ${CERES_VERSION_MAJOR})
 
+include(AppendTargetProperty)
 # Always build position-independent code (PIC), even when building Ceres as a
 # static library so that shared libraries can link against it, not just
 # executables (PIC does not apply on Windows).
@@ -192,12 +193,31 @@ if (NOT WIN32 AND NOT BUILD_SHARED_LIBS)
   # that support it (>= 2.8.9).  Otherwise, manually add the -fPIC flag as an
   # additional compile definitions for the target.
   if (CMAKE_VERSION VERSION_LESS "2.8.9")
-    set_target_properties(ceres PROPERTIES COMPILE_FLAGS "-fPIC")
+    append_target_property(ceres COMPILE_FLAGS "-fPIC")
   else()
+    # Use set_target_properties() not append_target_property() here as
+    # POSITION_INDEPENDENT_CODE is a binary ON/OFF switch.
     set_target_properties(ceres PROPERTIES POSITION_INDEPENDENT_CODE ON)
   endif()
 endif()
 
+# Use of -flto requires use of gold linker & LLVM-gold plugin, which might
+# well not be present / in use and without which files will compile, but
+# not link ('file not recognized') so explicitly check for support.
+#
+# Only use link-time optimisation (LTO) flags when building Ceres itself, as it
+# causes an issue with type_info::operator==() in gtest's
+# CheckedDowncastToActualType() in levenberg_marquardt_strategy_test &
+# gradient_checking_cost_function_test if enabled for the tests as well.
+include(CheckCXXCompilerFlag)
+check_cxx_compiler_flag("-flto" HAVE_LTO_SUPPORT)
+if (HAVE_LTO_SUPPORT)
+  message(STATUS "Enabling link-time optimization (-flto)")
+  append_target_property(ceres COMPILE_FLAGS "-flto")
+else ()
+  message(STATUS "Compiler/linker does not support link-time optimization (-flto).")
+endif (HAVE_LTO_SUPPORT)
+
 if (CMAKE_VERSION VERSION_LESS "2.8.12")
   # CMake version < 2.8.12 does not support target_compile_options(), warn
   # user that they will have to add compile flags to their own projects
@@ -254,7 +274,7 @@ if (BUILD_TESTING AND GFLAGS)
   add_library(gtest gmock_gtest_all.cc gmock_main.cc)
   if (BUILD_SHARED_LIBS)
     # Define gtest-specific shared library flags for compilation.
-    set_target_properties(gtest PROPERTIES COMPILE_DEFINITIONS
+    append_target_property(gtest COMPILE_DEFINITIONS
       GTEST_CREATE_SHARED_LIBRARY)
   endif()
 
@@ -278,7 +298,7 @@ if (BUILD_TESTING AND GFLAGS)
     target_link_libraries(${NAME}_test test_util ceres gtest)
     if (BUILD_SHARED_LIBS)
       # Define gtest-specific shared library flags for linking.
-      set_target_properties(${NAME}_test PROPERTIES COMPILE_DEFINITIONS
+      append_target_property(${NAME}_test COMPILE_DEFINITIONS
         GTEST_LINKED_AS_SHARED_LIBRARY)
     endif()
     add_test(NAME ${NAME}_test