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Commit 7723f50

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dcommanderdcommander
committed
Build: Don't modify CMAKE_C_FLAGS_* if specified
The build system originally force-enabled the maximum optimization level (-O3) with GCC because it significantly improved the performance of the C Huffman encoder on x86 platforms. Since libjpeg-turbo 1.5.x, the Huffman encoder has been SIMD-accelerated on x86 and Arm platforms, and in my testing on various Intel CPUs, the difference between -O2 and -O3 is no longer statistically significant. However, on certain Arm CPUs, I observe that grayscale decompression slows down by 16-27% with -O2 vs. -O3. Although modern versions of CMake use -O3 as the default optimization level for Release builds, -O2 is still the default optimization level for RelWithDebInfo builds. Thus, I am reluctant to change the default behavior of our build system. However, referring to #815, some users observe better performance with -O2 vs. -O3 on other Arm CPUs, so the build system needs to allow users to override the default behavior. Closes #815
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+23-8Lines changed: 23 additions & 8 deletions

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‎CMakeLists.txt‎

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+23-8Lines changed: 23 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -4,6 +4,15 @@ if(CMAKE_EXECUTABLE_SUFFIX)
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set(CMAKE_EXECUTABLE_SUFFIX_TMP ${CMAKE_EXECUTABLE_SUFFIX})
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endif()
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7+
set(CMAKE_C_FLAGS_RELEASE_INITIALIZED_TO_DEFAULT 1)
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if(CMAKE_C_FLAGS_RELEASE)
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set(CMAKE_C_FLAGS_RELEASE_INITIALIZED_TO_DEFAULT 0)
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endif()
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set(CMAKE_C_FLAGS_RELWITHDEBINFO_INITIALIZED_TO_DEFAULT 1)
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if(CMAKE_C_FLAGS_RELWITHDEBINFO)
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set(CMAKE_C_FLAGS_RELWITHDEBINFO_INITIALIZED_TO_DEFAULT 0)
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endif()
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project(libjpeg-turbo C)
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set(VERSION 3.1.1)
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set(COPYRIGHT_YEAR "1991-2024")
@@ -428,22 +437,28 @@ endif()
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if(CMAKE_COMPILER_IS_GNUCC OR CMAKE_C_COMPILER_ID MATCHES "Clang")
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# Use the maximum optimization level for release builds
431-
foreach(var CMAKE_C_FLAGS_RELEASE CMAKE_C_FLAGS_RELWITHDEBINFO)
432-
if(${var} MATCHES "-O2")
433-
string(REGEX REPLACE "-O2" "-O3" ${var} "${${var}}")
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foreach(build_type RELEASE RELWITHDEBINFO)
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if(CMAKE_C_FLAGS_${build_type} MATCHES "-O2" AND
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CMAKE_C_FLAGS_${build_type}_INITIALIZED_TO_DEFAULT)
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string(REGEX REPLACE "-O2" "-O3" CMAKE_C_FLAGS_${build_type}
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"${CMAKE_C_FLAGS_${build_type}}")
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endif()
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endforeach()
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endif()
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if(CMAKE_SYSTEM_NAME STREQUAL "SunOS")
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if(CMAKE_C_COMPILER_ID MATCHES "SunPro")
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# Use the maximum optimization level for release builds
441-
foreach(var CMAKE_C_FLAGS_RELEASE CMAKE_C_FLAGS_RELWITHDEBINFO)
442-
if(${var} MATCHES "-xO3")
443-
string(REGEX REPLACE "-xO3" "-xO5" ${var} "${${var}}")
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foreach(build_type RELEASE RELWITHDEBINFO)
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if(CMAKE_C_FLAGS_${build_type} MATCHES "-xO3" AND
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CMAKE_C_FLAGS_${build_type}_INITIALIZED_TO_DEFAULT)
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string(REGEX REPLACE "-xO3" "-xO5" CMAKE_C_FLAGS_${build_type}
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"${CMAKE_C_FLAGS_${build_type}}")
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endif()
445-
if(${var} MATCHES "-xO2")
446-
string(REGEX REPLACE "-xO2" "-xO5" ${var} "${${var}}")
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if(CMAKE_C_FLAGS_${build_type} MATCHES "-xO2" AND
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CMAKE_C_FLAGS_${build_type}_INITIALIZED_TO_DEFAULT)
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string(REGEX REPLACE "-xO2" "-xO5" CMAKE_C_FLAGS_${build_type}
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"${CMAKE_C_FLAGS_${build_type}}")
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endif()
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endforeach()
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endif()

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