From 435f6c5c89be038349b54cc175eda97b64e25aec Mon Sep 17 00:00:00 2001
From: Ryan Pavlik <ryan.pavlik@collabora.com>
Date: Tue, 12 May 2020 15:06:22 -0500
Subject: [PATCH] build: Allow enabling inter-procedural optimization in CMake
 builds, if supported.

---
 CMakeLists.txt                            | 9 +++++++++
 doc/changes/misc_features/mr.330.md       | 1 +
 src/xrt/state_trackers/gui/CMakeLists.txt | 3 +++
 3 files changed, 13 insertions(+)
 create mode 100644 doc/changes/misc_features/mr.330.md

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 6483ba4e8..9459fb8b3 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -19,6 +19,10 @@ list(APPEND CMAKE_MODULE_PATH "${CMAKE_CURRENT_SOURCE_DIR}/cmake")
 include(CMakeDependentOption)
 include(SPIR-V)
 include(GNUInstallDirs)
+if(NOT ${CMAKE_VERSION} VERSION_LESS 3.9)
+	include(CheckIPOSupported)
+	check_ipo_supported(RESULT HAS_IPO)
+endif()
 
 find_package(Eigen3 REQUIRED)
 find_package(Vulkan REQUIRED)
@@ -64,6 +68,7 @@ else()
 	find_package(OpenGL)
 endif()
 
+cmake_dependent_option(CMAKE_INTERPROCEDURAL_OPTIMIZATION "Enable inter-procedural (link-time) optimization" OFF "HAS_IPO" OFF)
 cmake_dependent_option(XRT_HAVE_WAYLAND "Enable Wayland support" ON "WAYLAND_FOUND AND WAYLAND_SCANNER_FOUND AND WAYLAND_PROTOCOLS_FOUND" OFF)
 cmake_dependent_option(XRT_HAVE_XLIB "Enable xlib support" ON "X11_FOUND" OFF)
 cmake_dependent_option(XRT_HAVE_XCB "Enable xcb support" ON "XCB_FOUND" OFF)
@@ -152,6 +157,10 @@ endif()
 # Default to PIC code
 set(CMAKE_POSITION_INDEPENDENT_CODE ON)
 
+# Describe IPO setting
+if(CMAKE_INTERPROCEDURAL_OPTIMIZATION)
+	message(STATUS "Inter-procedural optimization enabled")
+endif()
 
 ###
 # Decend into madness.
diff --git a/doc/changes/misc_features/mr.330.md b/doc/changes/misc_features/mr.330.md
new file mode 100644
index 000000000..120b0cf0f
--- /dev/null
+++ b/doc/changes/misc_features/mr.330.md
@@ -0,0 +1 @@
+build: Allow enabling inter-procedural optimization in CMake GUIs, if supported by platform and compiler.
diff --git a/src/xrt/state_trackers/gui/CMakeLists.txt b/src/xrt/state_trackers/gui/CMakeLists.txt
index 863a76f8d..ca119247c 100644
--- a/src/xrt/state_trackers/gui/CMakeLists.txt
+++ b/src/xrt/state_trackers/gui/CMakeLists.txt
@@ -1,6 +1,9 @@
 # Copyright 2019-2020, Collabora, Ltd.
 # SPDX-License-Identifier: BSL-1.0
 
+# c-imgui doesn't do well with IPO - lots of warnings.
+set(CMAKE_INTERPROCEDURAL_OPTIMIZATION OFF)
+
 set(GUI_SOURCE_FILES
 	gui_common.h
 	gui_imgui.h