From 494dc0382ac4809b83b7412792dae0ae1e76183d Mon Sep 17 00:00:00 2001
From: John Tramm <john.tramm@gmail.com>
Date: Mon, 20 Jan 2020 16:59:01 +0000
Subject: [PATCH] added IPO/LTO to cmake build commands, to be included when
 optimization is enabled.

---
 CMakeLists.txt                    | 28 ++++++++++++++++++++++++++++
 examples/xml/pincell/settings.xml |  2 +-
 src/event.cpp                     |  4 +++-
 3 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 95b334ce46..33911ac61b 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -69,6 +69,16 @@ if(HDF5_IS_PARALLEL)
   message(STATUS "Using parallel HDF5")
 endif()
 
+#===============================================================================
+# Enable interprocedural (link time) optimization if requested and supported
+#===============================================================================
+
+if (NOT (CMAKE_VERSION VERSION_LESS 3.9))
+  cmake_policy(SET CMP0069 NEW)
+  include(CheckIPOSupported)
+  check_ipo_supported(RESULT ipo_support_detected)
+endif()
+
 #===============================================================================
 # Set compile/link flags based on which compiler is being used
 #===============================================================================
@@ -110,6 +120,7 @@ message(STATUS "OpenMC Linker flags: ${ldflags}")
 
 endif()
 
+
 #===============================================================================
 # Update git submodules as needed
 #===============================================================================
@@ -205,6 +216,7 @@ target_include_directories(faddeeva
 )
 target_compile_options(faddeeva PRIVATE ${cxxflags})
 
+
 #===============================================================================
 # libopenmc
 #===============================================================================
@@ -313,6 +325,14 @@ endif()
 
 set_target_properties(libopenmc PROPERTIES
   OUTPUT_NAME openmc)
+  
+# Enable interprocedural (link time) optimization if requested and supported
+if(optimize)
+  if(ipo_support_detected)
+    set_property(TARGET libopenmc PROPERTY INTERPROCEDURAL_OPTIMIZATION TRUE)
+    message(STATUS "LTO enabled for libopenmc")
+  endif()
+endif()
 
 target_include_directories(libopenmc
   PUBLIC
@@ -365,6 +385,14 @@ add_executable(openmc src/main.cpp)
 target_compile_options(openmc PRIVATE ${cxxflags})
 target_link_libraries(openmc libopenmc)
 
+# Enable interprocedural (link time) optimization if requested and supported
+if(optimize)
+  if(ipo_support_detected)
+    set_property(TARGET openmc PROPERTY INTERPROCEDURAL_OPTIMIZATION TRUE)
+    message(STATUS "LTO enabled for openmc executable")
+  endif()
+endif()
+
 # Ensure C++14 standard is used. Starting with CMake 3.8, another way this could
 # be done is using the cxx_std_14 compiler feature.
 set_target_properties(
diff --git a/examples/xml/pincell/settings.xml b/examples/xml/pincell/settings.xml
index 741427460c..5845898c8d 100644
--- a/examples/xml/pincell/settings.xml
+++ b/examples/xml/pincell/settings.xml
@@ -3,7 +3,7 @@
 
   <!-- Define how many particles to run and for how many batches -->
   <run_mode>eigenvalue</run_mode>
-  <batches>20</batches>
+  <batches>100</batches>
   <inactive>10</inactive>
   <particles>1000</particles>
 
diff --git a/src/event.cpp b/src/event.cpp
index a40f67152c..4079d7790d 100644
--- a/src/event.cpp
+++ b/src/event.cpp
@@ -97,7 +97,9 @@ void process_calculate_xs_events(QueueItem* queue, int64_t n)
 {
   simulation::time_event_calculate_xs.start();
 
-  // TODO: Sort queue by particle type, material type, and energy
+  // TODO: If using C++17, perform a parallel sort of the queue
+  // by particle type, material type, and then energy, in order to
+  // improve cache locality and reduce thread divergence on GPU.
   //std::sort(queue, queue+n);
 
   // Save last_ members, find grid index