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CMake: Use -O2 instead of -O3 in CMAKE_BUILD_TYPE=Release.
-O3 doesn't seem useful for speed but it makes the code bigger. CMake makes is difficult for users to simply override the optimization level: CFLAGS / CMAKE_C_FLAGS aren't helpful because they go before CMAKE_C_FLAGS_RELEASE. Of course, users can override CMAKE_C_FLAGS_RELEASE directly but then they have to remember to add also -DNDEBUG to disable assertions. This commit changes -O3 to -O2 in CMAKE_C_FLAGS_RELEASE if and only if CMAKE_C_FLAGS_RELEASE cache variable doesn't already exist. So if a custom value is passed on the command line (or reconfiguring an already-configured build), the cache variable won't be modified.
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1 changed files with 19 additions and 0 deletions
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@ -74,9 +74,28 @@ string(REGEX REPLACE
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.*$"
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"\\1.\\2.\\3" PACKAGE_VERSION "${PACKAGE_VERSION}")
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# With several compilers, CMAKE_BUILD_TYPE=Release uses -O3 optimization
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# which results in bigger code without a clear difference in speed. If
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# no user-defined CMAKE_C_FLAGS_RELEASE is present, override -O3 to -O2
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# to make it possible to recommend CMAKE_BUILD_TYPE=Release.
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if(NOT DEFINED CMAKE_C_FLAGS_RELEASE)
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set(OVERRIDE_O3_IN_C_FLAGS_RELEASE ON)
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endif()
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# Among other things, this gives us variables xz_VERSION and xz_VERSION_MAJOR.
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project(xz VERSION "${PACKAGE_VERSION}" LANGUAGES C)
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if(OVERRIDE_O3_IN_C_FLAGS_RELEASE)
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# Looking at CMake's source, there aren't any _FLAGS_RELEASE_INIT
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# entries where "-O3" would appear as part of some other option,
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# thus a simple search and replace should be fine.
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string(REPLACE -O3 -O2 CMAKE_C_FLAGS_RELEASE "${CMAKE_C_FLAGS_RELEASE}")
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# Update the cache value while keeping its docstring unchanged.
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set_property(CACHE CMAKE_C_FLAGS_RELEASE
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PROPERTY VALUE "${CMAKE_C_FLAGS_RELEASE}")
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endif()
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# We need a compiler that supports enough C99 or newer (variable-length arrays
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# aren't needed, those are optional in C17). Setting CMAKE_C_STANDARD here
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# makes it the default for all targets. It doesn't affect the INTERFACE so
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