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alamahant
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Joined: 23 Mar 2019
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 Posted: Tue May 04, 2021 12:44 pm Post subject: -march=native vs -march=<specific-cpu> |
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Which one of the two produces more customized binaries?
Also for compiling gentoo-sources with USE="experimental"
CONFIG_MNATIVE_INTEL vs CONFIG_M<specific-cpu>
Are they identical?
Thanks a lot guys!
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redfish
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Joined: 27 Apr 2021
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| Posted: Tue May 04, 2021 1:30 pm Post subject: |
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-march=native is the same as -march=<cpufamily>, 'native' is a shortcut for selecting the cpu family of the build host.
| Quote: |
‘native’
This selects the CPU to generate code for at compilation time by determining the processor type of the compiling machine. Using -march=native enables all instruction subsets supported by the local machine (hence the result might not run on different machines). Using -mtune=native produces code optimized for the local machine under the constraints of the selected instruction set.
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https://gcc.gnu.org/onlinedocs/gcc/x86-Options.html |
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fedeliallalinea
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NeddySeagoon
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| Posted: Tue May 04, 2021 1:55 pm Post subject: |
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alamahant,
Ask gcc. | Code: | | gcc -### -E - -march=native 2>&1 | sed -r '/cc1/!d;s/(")|(^.* - )|( -mno-[^\ ]+)//g' |
From gcc 11.1.0 I get
| Code: | $ gcc -### -E - -march=native 2>&1 | sed -r '/cc1/!d;s/(")|(^.* - )|( -mno-[^\ ]+)//g'
-march=amdfam10 -mmmx -mpopcnt -msse -msse2 -msse3 -msse4a -m3dnow -mabm -mcx16 -mfxsr -msahf -mlzcnt -mprfchw --param l1-cache-size=64 --param l1-cache-line-size=64 --param l2-cache-size=512 -mtune=amdfam10 -dumpbase - |
which looks broken due to the trailing '-'
That may not really answer the question as -march=<cpu> may infer everything that -march=native sets explicitly.
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alamahant
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Joined: 23 Mar 2019
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| Posted: Tue May 04, 2021 2:01 pm Post subject: |
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Neddy
That is precisely why I posted.
If I run the above command with -march=native vs -march=hashwell in my case I get
| Code: |
gcc -### -E - -march=native 2>&1 | sed -r '/cc1/!d;s/(")|(^.* - )|( -mno-[^\ ]+)//g'
-march=haswell -mmmx -msse -msse2 -msse3 -mssse3 -mcx16 -msahf -mmovbe -maes -mpclmul -mpopcnt -mabm -mfma -mbmi -mbmi2 -mavx -mavx2 -msse4.2 -msse4.1 -mlzcnt -mrdrnd -mf16c -mfsgsbase -mfxsr -mxsave -mxsaveopt --param l1-cache-size=32 --param l1-cache-line-size=64 --param l2-cache-size=6144 -mtune=haswell
gcc -### -E - -march=hashwell 2>&1 | sed -r '/cc1/!d;s/(")|(^.* - )|( -mno-[^\ ]+)//g'
-march=nhashwell
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-march=native seems more comprehensive.
I do have also
| Code: |
*/* CPU_FLAGS_X86: aes avx avx2 f16c fma3 mmx mmxext pclmul popcnt sse sse2 sse3 sse4_1 sse4_2 ssse3
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still "native" seems more detailed.
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