69 lines
3.7 KiB
Plaintext
69 lines
3.7 KiB
Plaintext
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#This file contains the definitions for the optimization settings used by GentooLTO.
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#source this file directly in your make.conf if you want to cherry-pick settings
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#and don't want to use the make.conf.lto default configuration, defining the number of threads
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#to use during the LTO process beforehand:
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#NTHREADS="12"
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#source make.conf.lto.defines
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#Guidelines:
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#* Your CFLAGS should contain ${FLTO}
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#* If you want Graphite, include "${GRAPHITE}" in your CFLAGS
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#* If you want -fipa-pta, include "${IPAPTA}" in your CFLAGS
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#* Anything else is up to you, such as -march, -pipe, -O{3,2,s,1}, etc...
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#* CXXFLAGS should be set to CFLAGS
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#* Optionally, set other *FLAGS for languages compiled with GCC as well
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#* LDFLAGS of your Gentoo profile should be respected.
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# See make.conf.lto for more details.
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FLTO="-flto=${NTHREADS}"
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#FLTO is of the form -flto[=n] where n is the number of threads to use during linking.
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#It's usually a good idea to set this to the number of hardware threads in your system
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#You may also set this to "auto" to have gcc determine optimal number of cores (GCC 10+)
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GRAPHITE="-fgraphite-identity -floop-nest-optimize"
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#GRAPHITE contains Graphite specific optimizations and other optimizations that are disabled at O3 but don't influence the compiler's judgement.
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#Since GCC 8.1.0, -ftree-loop-distribution is enabled by default at -O3
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#NOTE: To use graphite, make sure you have gcc compiled with graphite support (add graphite to your USE). Otherwise GCC will complain!
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IPAPTA="-fipa-pta"
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#IPAPTA contains -fipa* opts that are disabled by default in GCC. These are interprocedural optimizations. For now this is only -fipa-pta.
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#This option increases compile times, but can potentially produce better binaries, especially with LTO.
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#Essentially, it allows the compiler to look into called function bodies when performing alias analysis
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SEMINTERPOS="-fno-semantic-interposition"
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#With -fno-semantic-interposition the compiler assumes that if interposition happens for functions
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#the overwriting function will have precisely the same semantics (and side effects).
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#Similarly if interposition happens for variables, the constructor of the variable will be the same.
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#The flag has no effect for functions explicitly declared inline (where it is never allowed for interposition to change semantics) and for symbols explicitly declared weak.
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NOCOMMON="-fno-common"
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# This option only affects C code. Only non-conformant C code needs -fcommon, which is enabled by default. Clear Linux leaves this flag off by default.
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# This is enabled by default with GCC 10 and is kept here only for documentation purposes. Use `-fcommon` to restore
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# GCC 9.x behaviour and below.
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SAFEST_FAST_MATH="-fno-math-errno -fno-trapping-math"
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SAFER_UNSAFE_MATH_OPTS="-fno-signed-zeros -fno-trapping-math -fassociative-math -freciprocal-math"
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SAFER_FAST_MATH="${SAFER_UNSAFE_MATH_OPTS} -fno-math-errno -ffinite-math-only -fno-rounding-math -fno-signaling-nans -fcx-limited-range -fexcess-precision=fast"
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#These are flags left off by default that we're planning to start using. Clear Linux uses these in lieu of full -ffast-math optimizations
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#They DO break compliance with ISO C++, so we'll be careful about introducing these.
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#Relevant discussion: https://gcc.gnu.org/ml/gcc/2017-09/msg00079.html
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#We may end up just going full -Ofast, with exceptions done in the usual way.
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DEVIRTLTO="-fdevirtualize-at-ltrans"
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#This allows GCC to perform devirtualization across object file boundaries using LTO.
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NOPLT="-fno-plt"
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#This option omits the PLT from the executable, making calls go through the GOT directly.
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#It inhibits lazy binding, so this is not enabled by default. If you use prelink, this is
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#strictly better than lazy binding.
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