build: Allow enabling inter-procedural optimization in CMake builds, if supported.

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.

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.

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