From 4bbff3fa215a7200cc6a9cd445e99efda219805c Mon Sep 17 00:00:00 2001
From: Christophe Giboudeaux <christophe@krop.fr>
Date: Wed, 13 Jan 2021 09:19:32 +0100
Subject: [PATCH] CMake: Use -ffat-lto-objects for static libraries with ltcg
 and GCC

CMake <= 3.19 adds the '-fno-fat-lto-objects' compiler flag
unconditionally when CMAKE_INTERPROCEDURAL_OPTIMIZATION is enabled.

This is fine for shared libraries but static ones need the opposite
compiler flag.

Task-number: QTBUG-89426
Change-Id: Ie5f48178803a270f6d94408f7a8e85d379eb123c
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
(cherry picked from commit 9563be2870b85309e163db950fefcb9200cac6f4)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
---
 cmake/QtModuleHelpers.cmake | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/cmake/QtModuleHelpers.cmake b/cmake/QtModuleHelpers.cmake
index cc755c9d006..806f97b8e19 100644
--- a/cmake/QtModuleHelpers.cmake
+++ b/cmake/QtModuleHelpers.cmake
@@ -82,6 +82,14 @@ function(qt_internal_add_module target)
         endif()
     endif()
 
+    if(FEATURE_ltcg AND GCC AND is_static_lib)
+        # CMake <= 3.19 appends -fno-fat-lto-objects for all library types if
+        # CMAKE_INTERPROCEDURAL_OPTIMIZATION is enabled. Static libraries need
+        # the opposite compiler option.
+        # (https://gitlab.kitware.com/cmake/cmake/-/issues/21696)
+        target_compile_options(${target} PRIVATE -ffat-lto-objects)
+    endif()
+
     if (ANDROID)
         qt_android_apply_arch_suffix("${target}")
     endif()