How to see which flags -march=native will activate?

To see command-line flags, use:

gcc -march=native -E -v - </dev/null 2>&1 | grep cc1

If you want to see the compiler/precompiler defines set by certain parameters, do this:

echo | gcc -dM -E - -march=native

It should be (-### is similar to -v):

echo | gcc -### -E - -march=native

To show the "real" native flags for gcc.

You can make them appear more "clearly" with a command:

gcc -### -E - -march=native 2>&1 | sed -r '/cc1/!d;s/(")|(^.* - )//g'

and you can get rid of flags with -mno-* with:

gcc -### -E - -march=native 2>&1 | sed -r '/cc1/!d;s/(")|(^.* - )|( -mno-[^\ ]+)//g'

You can use the -Q --help=target options:

gcc -march=native -Q --help=target ...

The -v option may also be of use.

You can see the documentation on the --help option here.

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