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@@ -1,17 +1,26 @@
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diff --git a/Source/CMakeLists.txt b/Source/CMakeLists.txt
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-index a90fa27..e5ecf8e 100644
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+index a90fa27..4e22383 100644
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--- a/Source/CMakeLists.txt
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+++ b/Source/CMakeLists.txt
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-@@ -15,10 +15,11 @@
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+@@ -15,10 +15,18 @@
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# under the License.
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# ----------------------------------------------------------------------------
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-+# O3DE change: use "-flto -ffat-lto-objects" instead of "-flto -fno-fat-lto-objects" for linux since it may remove some functions for static library which leads to undefined symbols
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- # Overwrite the LTO flags to force fat LTO; worth 3-4% performance
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+-# Overwrite the LTO flags to force fat LTO; worth 3-4% performance
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++# O3DE change: use "-ffat-lto-objects" instead of the default (-fno-fat-lto-objects)
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++# for linux since it may remove some functions for static library which leads to undefined symbols
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# See https://gitlab.kitware.com/cmake/cmake/-/issues/16808
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- if(CMAKE_CXX_COMPILER_ID MATCHES "GNU|Clang" AND ${CLI})
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+-if(CMAKE_CXX_COMPILER_ID MATCHES "GNU|Clang" AND ${CLI})
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- set(CMAKE_CXX_COMPILE_OPTIONS_IPO "-flto")
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-+ set(CMAKE_CXX_COMPILE_OPTIONS_IPO "-ffat-lto-objects")
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++# Note that
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++# 1. XCode does not support --ffat-lto-objects
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++# 2. Its not necessary to specify -flto in cmake >= 3.9 because it auto enables it for you if
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++# the target has set INTERPROCEDURAL_OPTIMIZATION target property.
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++# 3. If you use LTO, the bitcode emitted will only be usable on compiler versions equal to or higher
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++# than the version you made the lto-enabled static lib with, so you will have to get the minimum supported
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++# version of xcode and use xcode-select to compile with.
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++if(CMAKE_CXX_COMPILER_ID MATCHES "GNU|Clang" AND ${CLI} AND CMAKE_SYSTEM_NAME STREQUAL "Linux")
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++ set(CMAKE_CXX_COMPILE_OPTIONS_IPO "-ffat-lto-objects")
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endif()
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if(${DECOMPRESSOR})
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Nicholas Lawson