What exactly does -march=native do?

c++ c gcc gcc4
György Andrasek picture György Andrasek · Jun 10, 2010 · Viewed 8.7k times · Source

Gentoo Wiki told me the following:

Warning: GCC 4.2 and above support -march=native. -march=native applies additional settings beyond -march, specific to your CPU. Unless you have a specific reason not to (e.g. distcc cross-compiling), you should probably be using -march=native, rather than anything listed below.

What are those additional settings?

Answer

György Andrasek picture György Andrasek · Jun 10, 2010

Nevermind.

$ cc -march=core2 -E -v - </dev/null 2>&1 | grep cc1
 /[...]/cc1 -E -quiet -v -iprefix /[...]/4.3.2/ - -march=core2

$ cc -march=native -E -v - </dev/null 2>&1 | grep cc1
 /[...]/cc1 -E -quiet -v -iprefix /[...]/4.3.2/ - -march=core2 -mcx16 -msahf --param l1-cache-size=32 --param l1-cache-line-size=64 -mtune=core2

I'm starting to like this option a lot. -mcx16 and -msahf are two additional CPU instructions gcc can now use, which weren't available in earlier Core2's.

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