Revert increased inline threshold (iff Clang) to exported Ceres target.
- Increasing the inline threshold results in very variable performance
improvements, and could potentially confuse users if they are trying
to set the inline threshold themselves.
- As such, we no longer export our inline threshold configuration for
Clang, but instead document how to change it in the FAQs.
Change-Id: I88e2e0001e4586ba2718535845ed1e4b1a5b72bc
diff --git a/cmake/CeresConfig.cmake.in b/cmake/CeresConfig.cmake.in
index 9468279..9e29d7a 100644
--- a/cmake/CeresConfig.cmake.in
+++ b/cmake/CeresConfig.cmake.in
@@ -278,14 +278,6 @@
"${CERES_LOCATION} was built with C++11. Ceres target will add "
"C++11 flags to compile options for targets using it.")
endif()
- # Check for -inline-threshold Clang-specific flags.
- if (CMAKE_CXX_COMPILER_ID STREQUAL "Clang" AND
- CERES_INTERFACE_COMPILE_OPTIONS MATCHES ".*inline\\-threshold.*")
- message(STATUS "Ceres version ${CERES_VERSION} detected here: "
- "${CERES_LOCATION} will add flags to increase inline threshold "
- "to compile options for targets using it and are compiled with "
- "Clang (improves Eigen performance).")
- endif()
endif()
# Set legacy include directories variable for backwards compatibility.
diff --git a/docs/source/faqs.rst b/docs/source/faqs.rst
index 81bd9b7..badf90a 100644
--- a/docs/source/faqs.rst
+++ b/docs/source/faqs.rst
@@ -40,19 +40,29 @@
poor performance.
Ceres itself will always be compiled with an increased inline threshold
- (currently 600) when compiled with Clang. This increased threshold is also
- added to the interface flags for the exported Ceres CMake target provided
- that the CMake version is >= 2.8.12 (from which this was supported). This
- means that **any user code that links against Ceres using CMake >= 2.8.12
- (and is compiled with Clang, irrespective of what Ceres was compiled with)
- will automatically be compiled with the same increased inlining threshold
- used to compile Ceres**.
-
- If you are using CMake < 2.8.12 and Clang in your own code which uses Ceres
- we recommend that you increase the inlining threshold yourself using:
+ (currently 600) when compiled with Clang. To experiment with this in your
+ own code, you can use the following:
.. code-block:: cmake
+ # If using CMake >= 2.8.12:
+ # We recommend you use target_compile_options() to add the inlining flags
+ # to specific targets for fine grained control:
+ #
+ # Use a larger inlining threshold for Clang, since it can hobble Eigen,
+ # resulting in reduced performance. The -Qunused-arguments is needed because
+ # CMake passes the inline threshold to the linker and clang complains about
+ # it (and dies, if compiling with -Werror).
+ target_compile_options(<YOUR_TARGET_NAME> PUBLIC
+ $<$<CXX_COMPILER_ID:Clang>:-Qunused-arguments -mllvm -inline-threshold=600>)
+
+.. code-block:: cmake
+
+ # If using CMake < 2.8.12:
+ # On CMake < 2.8.12 target_compile_options() is not available, so you
+ # cannot add the flags only on a per-target level and must instead set them
+ # for all targets declared after the flags are updated:
+ #
# Use a larger inlining threshold for Clang, since it can hobble Eigen,
# resulting in reduced performance. The -Qunused-arguments is needed because
# CMake passes the inline threshold to the linker and clang complains about
diff --git a/internal/ceres/CMakeLists.txt b/internal/ceres/CMakeLists.txt
index 49f4de3..55643de 100644
--- a/internal/ceres/CMakeLists.txt
+++ b/internal/ceres/CMakeLists.txt
@@ -209,13 +209,6 @@
"compiler requires -std=c++11. The client is responsible for adding "
"-std=c++11 when using Ceres.")
endif()
-
- message("-- Warning: Detected CMake version: ${CMAKE_VERSION} < 2.8.12, "
- "which is the minimum required for compile options to be included in an "
- "exported CMake target, and the detected compiler is Clang. Cannot add "
- "increased -inline-threshold compile flag to exported Ceres target, but "
- "this is recommended to improve Eigen's performance on Clang. You will "
- "have to add this manually to targets using Ceres if desired.")
else()
# CMake version >= 2.8.12 supports target_compile_options().
if (CXX11 AND COMPILER_HAS_CXX11_FLAG)
@@ -228,30 +221,6 @@
target_compile_options(ceres PUBLIC
$<$<NOT:$<STREQUAL:$<TARGET_PROPERTY:LINKER_LANGUAGE>,C>>:-std=c++11>)
endif()
-
- # Export the use of a larger inlining threshold for Clang into the
- # exported Ceres target. The default setting for Clang hobbles Eigen and
- # increasing this can result in very significant performance improvements,
- # particularly in auto-diffed CostFunctions. Exporting this setting into
- # the Ceres target means any user code linking against Ceres (via CMake)
- # will use it. The -Qunused-arguments is needed because CMake passes the
- # inline threshold to the linker and clang complains about it and dies.
- #
- # We use a generator expression such that irrespective of whether Ceres was
- # compiled using Clang, if user code using Ceres is compiled with Clang
- # it will still inherit the flags (e.g. if Ceres compiled with GCC to get
- # OpenMP, but user code compiled with Clang).
- #
- # We use INTERFACE (not PUBLIC) here, and add the same flags to
- # CMAKE_CXX_FLAGS in the root Ceres CMakeLists such that even if
- # CMake < 2.8.12 is being used to compile Ceres with Clang, we will compile
- # Ceres, and all of the examples with the increased inline threshold.
- message("-- Adding compile flags to increase inline threshold to exported "
- "Ceres CMake target (improves Eigen performance). These will *only* be "
- "used if Clang is used to compile client code linking against Ceres (using "
- "CMake). They are not required, and will not be used, for GCC or MSVC.")
- target_compile_options(ceres INTERFACE
- $<$<CXX_COMPILER_ID:Clang>:-Qunused-arguments -mllvm -inline-threshold=600>)
endif()
if (BUILD_SHARED_LIBS)
